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Guides overview 15 pages

Apache ZooKeeper Operations Guides

Practical guides for running, troubleshooting, and monitoring Apache ZooKeeper in production.

Cassandra Operations Guides

Practical guides for running, troubleshooting, and monitoring Apache Cassandra in production.

Ceph Operations Guides

Practical guides for running, troubleshooting, and monitoring Ceph in production.

ClickHouse Operations Guides

Practical guides for running, troubleshooting, and monitoring ClickHouse in production.

CockroachDB Operations Guides

Practical guides for running, troubleshooting, and monitoring CockroachDB in production.

Elasticsearch Operations Guides

Practical guides for running, troubleshooting, and monitoring Elasticsearch in production.

HAProxy Operations Guides

Practical guides for running, troubleshooting, and monitoring HAProxy in production.

Kafka Operations Guides

Practical guides for running, troubleshooting, and monitoring Apache Kafka in production.

Kubernetes Operations Guides

Practical guides for running, troubleshooting, and monitoring Kubernetes in production.

Microsoft SQL Server Operations Guides

Practical guides for running, troubleshooting, and monitoring Microsoft SQL Server in production.

MySQL Operations Guides

Practical guides for running, troubleshooting, and monitoring MySQL in production.

NGINX Operations Guides

Practical guides for running, troubleshooting, and monitoring NGINX in production.

Operations Guides

Practical guides for running, troubleshooting, and monitoring production systems.

RabbitMQ Operations Guides

Practical guides for running, troubleshooting, and monitoring RabbitMQ in production.

Redis Operations Guides

Practical guides for running, troubleshooting, and monitoring Redis in production.

Cassandra Operations Guides 26 pages

Open the Cassandra Operations Guides hub

Cassandra Batch Too Large Warning: How To Fix It

Diagnose and remediate Cassandra batch size warnings and coordinator OOM caused by oversized multi-partition batches.

Cassandra Commit Log Disk Full: How To Fix It

Troubleshoot and recover when Cassandra commitlog segment exhaustion forces memtable flushes, overwhelms the write path, and blocks mutations.

Cassandra commitlog pending tasks: write-path I/O pressure

Diagnose and resolve sustained CommitLog PendingTasks in Apache Cassandra, where commitlog fsync bottlenecks delay write acknowledgments and cascade into dropped mutations.

Cassandra compaction death spiral: when writes outrun compaction throughput

Diagnose and recover from Cassandra compaction backlog when write rates exceed compaction throughput, causing SSTable accumulation, read amplification, and disk saturation.

Cassandra dropped mutations: silent write loss and load shedding

Diagnose and recover from Cassandra dropped mutations, where replicas silently discard writes past queue timeout, causing silent data loss and consistency gaps.

Cassandra dropped reads and other messages: reading nodetool tpstats Dropped

Interpret nodetool tpstats Dropped counters, correlate message types with thread pool saturation, and understand what each scope means for reads, writes, hints, and repairs.

Cassandra GC death spiral: long pauses, gossip flapping, and recovery

Operational guide to identifying, diagnosing, and recovering from Cassandra GC death spirals caused by heap pressure, gossip timeouts, and hint replay floods.

Cassandra gossip flapping: nodes bouncing UP and DOWN

Diagnose and stop Cassandra nodes flapping between UP and DOWN states caused by GC pressure, network issues, or gossip saturation.

Cassandra hint overflow: max_hint_window expiry and silent data divergence

Diagnose and recover from Cassandra hint window expiration, hint accumulation, and the silent data divergence that follows extended replica outages.

Cassandra hints accumulating: hinted handoff backlog and replay storms

Diagnose and resolve Cassandra hinted handoff backlog and replay storms before coordinator disk exhaustion and cascading replica failures.

Cassandra hot partition: when one key saturates a replica set

Diagnose and mitigate hot partitions in Apache Cassandra when a single key concentrates traffic, saturating replicas and spiking tail latency.

Cassandra killed by the Linux OOM killer: off-heap memory and RSS

Diagnose and prevent Linux OOM kills on Cassandra nodes when off-heap RSS exceeds available RAM despite a healthy JVM heap.

Cassandra large partition pathology: Compacting large partition warnings and reads

Diagnose and fix Cassandra large partitions when you see Compacting large partition warnings, read latency spikes, and JVM heap pressure.

Cassandra native transport not running: node UP in gossip but refusing CQL clients

Diagnose why a Cassandra node shows UN in gossip but refuses CQL client connections, and restore native transport safely.

Cassandra node showing DN in nodetool status: gossip, phi, and recovery

Diagnose why Cassandra nodes appear as DN in nodetool status, understand phi accrual failure detection, and recover from gossip flapping and network partitions.

Cassandra Not enough space for compaction: STCS space amplification and recovery

Operational guide to diagnosing and recovering from Cassandra disk space exhaustion caused by STCS compaction space amplification, including per-strategy headroom and emergency remediation.

Cassandra OperationTimedOutException: client-side timeouts vs server timeouts

Distinguish client-side driver timeouts from server-side ReadTimeout and WriteTimeout in Cassandra, correlate the right signals, and turn the correct knob.

Cassandra pending compactions growing: the compaction backlog runbook

Diagnose and recover from growing Cassandra compaction backlogs before read latency and disk space spiral out of control.

Cassandra ReadTimeoutException: diagnosing coordinator read timeouts

Diagnose server-side Cassandra read timeouts where the coordinator fails to gather enough replica responses within read_request_timeout_in_ms.

Cassandra repair not running: the silent gap that resurrects deleted data

Detect when Cassandra anti-entropy repair stalls, diagnose why repair fails to complete within gc_grace_seconds, and prevent silent tombstone resurrection.

Cassandra Scanned over N tombstones warning: finding the offending query

Diagnose Cassandra tombstone warnings by identifying the table, partition, and query behind excessive tombstone scans before reads abort or trigger GC pressure.

Cassandra TombstoneOverwhelmingException: reads aborted by tombstone_failure_threshold

Operational guide to diagnosing and fixing Cassandra reads aborted by tombstone_failure_threshold, including per-table diagnosis, compaction, and repair correlation.

Cassandra Too many open files: file descriptor exhaustion

Diagnose and resolve file descriptor exhaustion in Apache Cassandra, including ulimit tuning, SSTable growth, and connection leak detection.

Cassandra too many SSTables per table: read amplification and how to fix it

Fix high SSTable counts in Cassandra before read amplification crushes latency. Diagnosis, emergency compaction, and root-cause remediation for LCS and STCS.

Cassandra UnavailableException: not enough replicas for the consistency level

Diagnose and recover from Cassandra UnavailableException when the coordinator cannot satisfy the requested consistency level due to insufficient live replicas.

Cassandra zombie data resurrection: gc_grace_seconds and unrepaired tombstones

Deleted data reappears when tombstones expire before repair reconciles them across replicas. Detect the silent failure and recover safely.

Ceph Operations Guides 15 pages

Open the Ceph Operations Guides hub

Ceph backfill_toofull: recovery blocked because target OSDs are full

Diagnose and resolve Ceph backfill_toofull PGs where recovery stalls because target OSDs exceed the backfillfull ratio.

Ceph blocked ops: client I/O stuck behind a single slow OSD

Localize the single slow OSD blocking client writes, read the op pipeline stage, and decide disk vs network vs op queue.

Ceph BLUEFS_SPILLOVER: RocksDB metadata spilling onto the slow device

Diagnose and fix Ceph BLUEFS_SPILLOVER when BlueStore RocksDB metadata overflows the DB partition and tanks OSD commit latency.

Ceph capacity death spiral: an OSD fails and recovery has nowhere to go

An OSD fails on a hot cluster and backfill stalls because surviving OSDs are past the backfillfull ratio. Diagnose BACKFILL_TOOFULL and stalled recovery.

Ceph FS_DEGRADED: standby MDS failed to take over a rank

Diagnose CephFS FS_DEGRADED when a standby MDS does not promote to a failed rank, and recover before the cluster escalates to MDS_ALL_DOWN.

Ceph HEALTH_ERR: reading the umbrella status and finding the real fault

How to interpret HEALTH_ERR as an umbrella status and drill into ceph health detail to find the specific child fault.

Ceph LARGE_OMAP_OBJECTS: the RGW bucket-index OMAP storm and resharding

Diagnose and fix Ceph LARGE_OMAP_OBJECTS warnings caused by oversized RGW bucket-index OMAP shards. Covers identification, dynamic and manual resharding, and prevention.

Ceph monitor quorum lost: the cluster can no longer update its maps

Diagnose and recover a Ceph cluster that has lost monitor quorum and can no longer commit map updates.

Ceph OSD down: telling a dead disk apart from a network blip

Triage a Ceph OSD marked down by separating disk failure from network loss, OOM-kill, and daemon crashes before recovery starts.

Ceph OSD flapping: OSDs cycling up and down and the peering storm that follows

Diagnose and stabilize Ceph OSD flapping before the peering storm cascades into a cluster-wide outage.

Ceph OSD_FULL: all writes stopped at the 95% full ratio

Diagnose and recover from a Ceph OSD_FULL condition where all writes stop at the 95% full ratio, and prevent it from recurring.

Ceph PG down: no surviving replica for reads or writes

Diagnose and recover Ceph placement groups stuck in the down state, where no surviving replica can serve reads or writes.

Ceph PG inconsistent (OSD_SCRUB_ERRORS): scrub found replica divergence

Ceph scrub found replica divergence. Diagnose which copy is corrupt before running ceph pg repair, or you may propagate the corruption.

Ceph slow requests (SLOW_OPS): operations blocked past osd_op_complaint_time

Diagnose and resolve Ceph SLOW_OPS warnings where operations exceed osd_op_complaint_time (default 30s) and stall in the OSD pipeline.

Ceph unfound objects: the cluster cannot locate a surviving copy

Diagnosing and resolving Ceph unfound objects when all replicas or EC chunks are on down or destroyed OSDs.

ClickHouse Operations Guides 24 pages

Open the ClickHouse Operations Guides hub

ClickHouse Active Part Count Growing: How To Fix

Operational guide to diagnosing and stopping ClickHouse active part count growth before it triggers insert delays, throttling, or too-many-parts errors.

ClickHouse checksum mismatch and broken parts: detecting data corruption

Detect and remediate ClickHouse data corruption from checksum mismatches, broken parts, and detached parts before replication divergence spreads.

ClickHouse DB::Exception: Too many parts - causes and fixes

Troubleshoot and resolve ClickHouse exception code 252 when inserts fail because a partition has accumulated too many active parts.

ClickHouse DelayedInserts climbing: the warning before too-many-parts

Understand why ClickHouse DelayedInserts climbs, how the insert throttle works, and what to check before inserts start rejecting.

ClickHouse full table scan: partition pruning failures and the primary key

Diagnose why ClickHouse queries scan every row and how to fix partition pruning and primary key misalignment.

ClickHouse long-running queries: finding and killing the resource hog

Operational guide for identifying, diagnosing, and terminating ClickHouse queries that consume excessive resources or stall indefinitely.

ClickHouse Memory limit (for query) exceeded: per-query limits and GROUP BY/JOIN blowups

Troubleshoot ClickHouse error code 241 when per-query memory limits breach, including high-cardinality GROUP BY, unbounded DISTINCT, and Cartesian-product JOINs.

ClickHouse Memory limit (total) exceeded - server-wide memory pressure and fixes

Diagnose and fix the ClickHouse server-wide MEMORY_LIMIT_EXCEEDED error (code 241) when MemoryTracking hits max_server_memory_usage.

ClickHouse memory pressure death spiral: runaway queries, retries, and OOM

Diagnose and break the feedback loop where memory pressure, query kills, retries, and spill-to-disk compound into cascading failure.

ClickHouse merge death spiral: when parts accumulate faster than merges consolidate

Break the feedback loop where ClickHouse inserts outrun background merges, parts pile up, and writes are delayed or rejected.

ClickHouse merges not keeping up: diagnosing a stalled or starved merge pool

Diagnose why ClickHouse background merges stall, starve, or fall behind, and fix the root cause before parts accumulate into a rejection crisis.

ClickHouse mutation stuck: parts_to_do not decreasing and how to recover

Diagnose and recover stuck ClickHouse mutations when parts_to_do stops decreasing, including quick checks, root causes, and safe remediation steps.

ClickHouse mutations silently blocking merges: the hidden cause of part growth

Why ALTER UPDATE/DELETE mutations starve the merge pool, how to spot the starvation before parts explode, and what to do about it.

ClickHouse No space left on device: emergency recovery when the data disk fills

Emergency recovery procedures and root-cause analysis for ClickHouse servers that hit disk-full conditions, including safe space reclamation and merge death-spiral prevention.

ClickHouse query error rate high: reading exception codes 241, 252, and 999

Triage a ClickHouse query error spike by exception code. Diagnose memory limits, too many parts, ZooKeeper issues, and schema drift using system.query_log and system.events.

ClickHouse query latency P99 spikes: tail latency, hot shards, and cold data

Diagnose and fix ClickHouse P99 query latency spikes caused by tail latency, hot shards, cold data, and resource contention.

ClickHouse Replica is lost: SYSTEM RESTORE REPLICA and recovering a diverged replica

Diagnose and recover a ClickHouse replica that has silently diverged from its peers using SYSTEM RESTART REPLICA and the supported limits of SYSTEM RESTORE REPLICA.

ClickHouse replication lag: absolute_delay, queue_size, and catch-up diagnosis

Diagnose ClickHouse replication lag using system.replicas, system.replication_queue, and background pool signals. Learn to tell a saturated fetch pool from a stuck mutation or a readonly replica.

ClickHouse replication queue stuck: num_tries, last_exception, and dead entries

Diagnose and fix stuck ClickHouse replication queue entries by reading num_tries, last_exception, and entry types instead of relying on delay alone.

ClickHouse small inserts anti-pattern: why single-row inserts melt the merge pool

Understand how single-row and micro-batch inserts create part accumulation in ClickHouse, the signals that expose the pattern, and the client-side fixes that actually work.

ClickHouse Table is in readonly mode: is_readonly on replicated tables and how to fix it

Diagnose and recover replicated ClickHouse tables stuck in readonly mode caused by lost Keeper sessions, coordination failures, or quorum loss.

ClickHouse too many partitions: why over-partitioning multiplies your part count

How high-cardinality partition keys in ClickHouse create thousands of isolated part pools, why parts never merge across partitions, and how this drives per-partition limit violations.

ClickHouse Too many simultaneous queries: max_concurrent_queries and query storms

Diagnose and fix ClickHouse query storms when max_concurrent_queries is reached, including retry amplification and concurrency saturation.

ClickHouse ZooKeeper session has expired: causes, recovery, and tuning

Diagnose and recover when ClickHouse replicas lose ZooKeeper sessions, become read-only, and stop accepting writes.

CockroachDB Operations Guides 24 pages

Open the CockroachDB Operations Guides hub

CockroachDB certificate expired: TLS handshake failures and online rotation

Detect, diagnose, and recover from expired CockroachDB TLS certificates using online rotation via SIGHUP.

CockroachDB changefeed lag: changefeed_max_behind_nanos and the GC time bomb

Diagnose and fix CockroachDB changefeed lag before protected timestamps block MVCC garbage collection and fill your disk.

CockroachDB clock skew cascade: how shared NTP drift causes quorum loss

Diagnose and resolve CockroachDB clock skew cascades where shared NTP drift causes multiple node self-terminations and quorum loss.

CockroachDB clock synchronization error: this node is more than 500ms away from at least half of the known nodes

Diagnose and fix the CockroachDB clock synchronization error that causes nodes to self-terminate when clock drift exceeds the max-offset threshold.

CockroachDB compaction backlog growing: when Pebble can't keep pace with writes

Diagnose a growing Pebble compaction backlog in CockroachDB before it triggers write stalls, and learn how to restore balance between write ingestion and compaction throughput.

CockroachDB connection storm after failover: reconnect stampedes and surviving-node overload

Diagnose and mitigate reconnect stampedes that overload surviving CockroachDB nodes after failover, with metrics, quick checks, and client pool tuning.

CockroachDB consistency check failed: checksum mismatches and confirmed corruption

Operational reference for diagnosing and responding to CockroachDB consistency check failures, checksum mismatches, and confirmed data corruption.

CockroachDB context deadline exceeded: timeouts, slow ranges, and overload

Diagnose CockroachDB context deadline exceeded errors by tracing KV exec latency, round-trip latency, L0 sublevels, and admission control queues to find the slow layer.

CockroachDB CPU saturation: Raft ticking, SQL execution, and the per-node ceiling

Diagnose CockroachDB CPU saturation by separating Raft tick overhead, SQL execution, GC pressure, and I/O-bound system time from cluster-wide averages.

CockroachDB disk stall detected: storage_disk_stalled and node self-termination

Diagnose and resolve CockroachDB storage_disk_stalled alerts before the node self-terminates to prevent data inconsistency.

CockroachDB error 53200: SQL memory budget exhausted and query rejection

Diagnose and fix CockroachDB error 53200 when per-node SQL memory budget exhaustion causes query rejection or disk spills.

CockroachDB LSM compaction death spiral: L0 sublevels, read amplification, and write stalls

Diagnose and break the LSM compaction death spiral in CockroachDB by monitoring L0 sublevels, read amplification, and write stalls before nodes lose leases.

CockroachDB memory pressure, GC thrashing, and Raft liveness failure

Diagnose and resolve the cycle where Go heap growth triggers long GC pauses, node liveness loss, and oscillating cluster availability.

CockroachDB node liveness failure: heartbeats, lease redistribution, and flapping

Diagnose and fix CockroachDB node liveness failures, from disk stalls and GC pauses to network partitions and flapping availability.

CockroachDB out of memory: sys_rss, --cache, --max-sql-memory, and the OOM killer

Diagnose CockroachDB OOM kills by tracking sys_rss, CGo allocations, SQL memory budget, and the sizing relationship between --cache, --max-sql-memory, and container limits.

CockroachDB Pebble write stalls: when the storage engine refuses writes

Diagnose and resolve CockroachDB Pebble write stalls when the storage engine pauses writes due to LSM compaction debt.

CockroachDB ReadWithinUncertaintyInterval restarts: the near-diagnostic signal of clock skew

Diagnose and resolve ReadWithinUncertaintyInterval restarts in CockroachDB, the near-diagnostic signal of clock skew between nodes.

CockroachDB result is ambiguous: ambiguous commit errors and how to handle them

Diagnose and handle CockroachDB result is ambiguous errors (code 40003), from leaseholder changes to network timeouts, with practical retry and idempotency guidance.

CockroachDB RETRY_WRITE_TOO_OLD: the most common contention restart and how to kill it

Diagnose and eliminate CockroachDB writetooold transaction restarts caused by hot keys, sequential writes, and wide transactions under SERIALIZABLE isolation.

CockroachDB SQL error rate: XX000 internal errors and error-code triage

Triage CockroachDB SQL error rates by PostgreSQL error code, distinguish XX000 internal errors from retriable failures, and know when to page.

CockroachDB store is full: emergency disk recovery and why deletes don't free space

Emergency recovery procedures when CockroachDB stores run out of disk space, and why SQL DELETE operations do not immediately reclaim space.

CockroachDB too many connections: sql_conns, pooling, and goroutine pressure

Diagnose and resolve connection pressure in CockroachDB using sql_conns, goroutine counts, and file descriptor metrics before they cascade into node failure.

CockroachDB TransactionRetryWithProtoRefreshError: RETRY_SERIALIZABLE causes and fixes

Diagnose and fix CockroachDB RETRY_SERIALIZABLE errors by distinguishing writetooold, readwithinuncertainty, and txnpush causes and implementing proper retry logic.

How To Fix CockroachDB Admission Control Throttling

Diagnose CockroachDB admission control throttling across its five queues, correlate store-write depth with LSM health, and determine when queuing is protective versus capacity-limiting.

Docker Operations Guides 7 pages

Open the Docker Operations Guides hub

Docker commands hang: docker ps, inspect, and exec freezes

Diagnose and recover when Docker CLI commands hang while containers keep running. Covers daemon deadlock, storage driver hangs, and plugin failures.

Docker container cannot connect to another container

Diagnose and fix inter-container connectivity issues in Docker, including DNS failures, network misconfiguration, and application binding problems.

Docker Container Running But Unhealthy: How To Fix

Diagnose why a Docker container is running but marked unhealthy, inspect health state and failure streaks, and fix health check command, timing, and resource issues.

Docker daemon not responding: how to troubleshoot a hung dockerd

Step-by-step guide to diagnosing and recovering a hung or unresponsive Docker daemon, including socket probes, containerd checks, storage driver investigation, and live-restore behavior.

Docker image cleanup: safe pruning strategies for production hosts

Safe commands and filters to reclaim Docker disk space without stopping running containers or deleting data you still need.

Docker image pull failures: registry, network, and auth diagnosis

Diagnose why docker pull fails across registry reachability, network path, and authentication. Step-by-step checks, signals, and fixes for production operators.

Docker published port not reachable: troubleshooting -p and EXPOSE

Diagnose why a Docker container's published port is unreachable from the host or remote clients, covering mapping, bind addresses, application listeners, and firewall rules.

Elasticsearch Operations Guides 27 pages

Open the Elasticsearch Operations Guides hub

Elasticsearch All Shards Failed: How To Fix It

Diagnose and fix Elasticsearch search_phase_execution_exception when all shards fail, distinguishing data unavailability from query errors and resource exhaustion.

Elasticsearch ALLOCATION_FAILED after max retries: reroute and corrupt shard recovery

Recover Elasticsearch shards stuck in ALLOCATION_FAILED after exceeding max retries, including reroute API usage and corrupt shard recovery paths.

Elasticsearch cluster health red: unassigned primaries and how to recover

Diagnose and recover from a red Elasticsearch cluster when primary shards are unassigned, including allocation explain, disk watermarks, and manual reroute.

Elasticsearch cluster health yellow: unassigned replicas vs real allocation blocks

Distinguish benign yellow cluster states from real allocation blockers. Diagnose unassigned replicas, disk watermarks, and shard allocation failures in Elasticsearch.

Elasticsearch cluster state too large: field count, index count, and per-node heap

Diagnose and fix an oversized Elasticsearch cluster state that burns heap on every node and overwhelms the master.

Elasticsearch cluster_block_exception: blocked by, the read-only blocks explained

Map Elasticsearch cluster_block_exception codes to their root causes and clear read-only blocks on indices or the cluster.

Elasticsearch coordinating node overload: aggregation merge, heap spikes, and 429s

Diagnose and fix Elasticsearch coordinating node overload caused by aggregation merges, heap spikes, and circuit breaker trips that return HTTP 429.

Elasticsearch disk full: emergency recovery and freeing space safely

Emergency recovery steps when Elasticsearch data nodes exhaust disk space, including safe deletion order, replica reduction, and clearing flood-stage read-only blocks.

Elasticsearch EsRejectedExecutionException: write thread pool rejections and HTTP 429

Diagnose and fix Elasticsearch write thread pool rejections that surface as EsRejectedExecutionException and HTTP 429 responses.

Elasticsearch expensive queries: leading wildcards, regex, deep pagination, and scripts

Find and fix Elasticsearch queries that burn CPU and heap. Covers leading wildcards, regex, deep pagination, scripts, and the diagnostic signals that expose them.

Elasticsearch fielddata circuit breaker tripped: text-field aggregations and the keyword fix

Diagnose and fix Elasticsearch fielddata circuit breaker trips caused by aggregating or sorting on analyzed text fields. Use keyword sub-fields and monitor the right signals.

Elasticsearch FORBIDDEN/12/index read-only / allow delete (api) — flood stage recovery

Recover from Elasticsearch cluster_block_exception when flood-stage disk watermark sets index.blocks.read_only_allow_delete, blocking writes.

Elasticsearch heap pressure death spiral: GC, node removal, and the cascade

How sustained heap pressure above 85% triggers old GC pauses, node removal, and cascading shard reallocation in Elasticsearch clusters, and how to break the cycle.

Elasticsearch ILM stuck: indices not rolling over, shrinking, or deleting

Diagnose and unstick Elasticsearch Index Lifecycle Management when indices fail to advance through rollover, shrink, or delete actions.

Elasticsearch indexing rate dropped to zero: where the write path stalls

Diagnose why Elasticsearch indexing stops despite active ingestion. Covers write thread pool saturation, merge storms, ingest pipeline bottlenecks, unassigned primaries, circuit breakers, and read-only disk blocks.

Elasticsearch Limit of total fields [1000] in index has been exceeded — mapping explosion

Diagnose and fix the Elasticsearch illegal_argument_exception when dynamic mapping causes the index total fields limit of 1000 to be exceeded.

Elasticsearch long GC pauses: old-generation stop-the-world and node drops

Diagnose and fix Elasticsearch old-generation GC pauses that trigger stop-the-world events, fault-detection timeouts, and cascading node removals.

Elasticsearch mapper_parsing_exception: type conflicts and failed document indexing

Fix mapper_parsing_exception errors in Elasticsearch caused by type conflicts, strict mapping, and malformed fields. Learn to detect, diagnose, and reindex safely.

Elasticsearch mapping explosion: dynamic mapping, cluster state bloat, and master pressure

Diagnose and fix Elasticsearch mapping explosion from dynamic mapping, including field limits, cluster state bloat, and master node pressure.

Elasticsearch master instability: frequent elections and metadata overload

Diagnose and fix Elasticsearch master node flapping caused by cluster state metadata overload, GC pauses, and election timeouts.

Elasticsearch master_not_discovered_exception: no elected master and stalled writes

Diagnose and resolve Elasticsearch master_not_discovered_exception when no master is elected and writes stall due to quorum loss, GC pauses, network partitions, or cluster state overload.

Elasticsearch merge storms: segment explosion, I/O saturation, and refresh tuning

Diagnose and fix Elasticsearch merge storms caused by segment explosion, I/O saturation, and aggressive refresh intervals.

Elasticsearch node left the cluster: fault detection, reallocation, and recovery

Diagnose and recover when an Elasticsearch node departs unexpectedly, including fault detection mechanics, delayed reallocation, and voting configuration cleanup.

Elasticsearch node OOM-killed: heap ceiling, page cache, and container limits

Diagnose and fix Elasticsearch nodes killed by the Linux OOM-killer due to heap, off-heap, page cache, and container memory limit pressure.

Elasticsearch this action would add too many shards: max_shards_per_node limit

Fix the Elasticsearch validation_exception when cluster.max_shards_per_node is breached. Why raising the limit is wrong and how to consolidate shards.

Elasticsearch unassigned shards: reading allocation explain and fixing each reason

Diagnose and resolve unassigned shards in Elasticsearch by reading the allocation explain API, interpreting unassigned.reason values, and applying targeted fixes per failure mode.

Fix Elasticsearch CircuitBreakingException Errors

Diagnose and resolve the Elasticsearch [parent] Data too large CircuitBreakingException. Covers real-memory tracking, heap consumers, task cancellation, and prevention.

HAProxy Operations Guides 19 pages

Open the HAProxy Operations Guides hub

HAProxy 400 And 408 Request Errors: How To Fix

Troubleshoot HAProxy 400 Bad Request and 408 Request Timeout spikes: tune.bufsize, PROXY protocol mismatches, HTTP/2 framing, request smuggling, and Slowloris.

HAProxy 502 Bad Gateway: Causes And Fixes

Diagnose HAProxy 502 Bad Gateway errors by separating connection failures (econ) from broken responses (eresp), using stats counters, termination flags, and show errors.

HAProxy 503 Service Unavailable: no server is available to handle this request

Diagnose and fix HAProxy 503 Service Unavailable errors: all servers DOWN, queue overflow, maxconn saturation, and routing gaps, using stats and log termination codes.

HAProxy 504 Gateway Timeout: timeout server and the backend timeout cascade

Why HAProxy emits 504 Gateway Timeout when timeout server fires, how the backend timeout cascade builds, and how to diagnose it with rtime, qcur, econ, and frontend vs backend 5xx.

HAProxy 5xx delta: telling HAProxy-generated errors from backend errors

Use the delta between frontend hrsp_5xx and backend hrsp_5xx to isolate errors HAProxy generated itself (503, 504, 502) from errors your backend servers returned.

HAProxy backend losing servers: active server count and cascade risk

How to detect and respond when HAProxy backends lose servers: the act/bck signals, why BACKEND status stays UP, and how to judge cascade risk before the last server fails.

HAProxy backend queue building (qcur): requests waiting for a free server slot

What qcur means in HAProxy stats, why the backend queue grows, how to diagnose it, and how to fix saturation before it turns into 503s.

HAProxy connection errors (econ): backend connections refused, timed out, or reset

Troubleshoot rising HAProxy econ counters: how to tell refused from timed-out from reset backend connections, find the root cause, and prevent recurrence.

HAProxy DNS resolver failure: stale IPs and silently misrouted traffic

Diagnose HAProxy DNS resolver failures in server-template and service-discovery deployments where stale IPs silently misroute traffic while servers report UP.

HAProxy ephemeral port exhaustion: TIME_WAIT and backend connection churn

Diagnose and fix HAProxy ephemeral port exhaustion: why backend connection churn fills TIME_WAIT, how to confirm it with econ spikes and ss, and how http-reuse, a wider port range, and tcp_tw_reuse fix it.

HAProxy health check L4TOUT and L4CON: server marked DOWN and unreachable

What L4TOUT and L4CON mean in HAProxy health check output, how to tell a timeout from an immediate refusal, and how to find whether the fault is the server, the network, or HAProxy itself.

HAProxy health check L7STS: server DOWN on the wrong HTTP status

What HAProxy's L7STS health check code means, why a server goes DOWN on an unexpected HTTP status, and how to tell L7STS apart from L7RSP and L7TOUT.

HAProxy health checks green but the application is broken: when UP does not mean healthy

All HAProxy servers show UP but users get 5xx. Why TCP and stub HTTP health checks lie, how to confirm it with per-server hrsp_5xx, and how to fix the check.

HAProxy Idle_pct dropping: event-loop CPU saturation and the busy-polling trap

What HAProxy Idle_pct actually measures, how to diagnose event-loop CPU saturation when it drops, and why the metric is meaningless when busy-polling is enabled.

HAProxy kernel accept-queue overflow: silent SYN drops and somaxconn

Clients time out but HAProxy looks perfectly healthy. How to detect and fix Linux accept-queue overflow (ListenOverflows, ListenDrops, somaxconn) in front of HAProxy.

HAProxy maxconn reached: new connections queued and rejected

Diagnose and fix HAProxy maxconn saturation: CurrConns flat at Maxconn, connections queuing in the kernel backlog, and clients timing out while CPU looks fine.

HAProxy scur approaching slim: the concurrent-session saturation signal

What the HAProxy scur/slim ratio means at the global, frontend, backend, and server levels, how to alert on it, and what to do when concurrent sessions approach the configured limit.

HAProxy SSL certificate expired: total TLS failure and how to catch it first

An expired HAProxy frontend certificate means instant, total TLS failure for every client. How to confirm it, hot-fix it without a reload, and alert on expiry 30 days before it pages you.

HAProxy Too many open files: file descriptor exhaustion and refused connections

Diagnose and fix HAProxy file descriptor exhaustion: EMFILE on accept, refused connections, ulimit vs maxconn sizing, and reload-related FD leaks.

Kafka Operations Guides 22 pages

Open the Kafka Operations Guides hub

Kafka __consumer_offsets growing huge: compaction failure on the offsets topic

Diagnose and fix unbounded growth of Kafka's __consumer_offsets topic caused by a stalled or crashed log cleaner thread.

Kafka ActiveControllerCount not equal to 1: no controller or split brain

Diagnose and recover when the cluster-wide sum of Kafka ActiveControllerCount deviates from 1, indicating no active controller or split brain.

Kafka Broker May Not Be Available: How To Fix It

Diagnose why Kafka clients fail with 'Broker may not be available' even when the bootstrap server is reachable. Covers advertised.listeners misconfiguration, TLS and SASL handshake failures, firewall blocks, and genuine broker outages.

Kafka Broker Out Of Disk: How To Fix It

Diagnose and recover when a Kafka broker exhausts disk space on its log directories, including the cliff-edge shutdown behavior, uneven directory fill, and silent compaction failures.

Kafka CommitFailedException: rebalanced-out consumers and poll loop timeouts

Operational guide to diagnosing CommitFailedException caused by consumers evicted after exceeding max.poll.interval.ms during slow batch processing, and stopping rebalance storms.

Kafka consumer group rebalancing too often: heartbeats, session timeout, and assignors

Diagnose and fix Kafka consumer groups that rebalance too frequently. Covers heartbeat timeouts, session expiry, max.poll.interval.ms, assignor behavior, and static membership.

Kafka consumer rebalance storm: stuck in PreparingRebalance and max.poll.interval.ms

Diagnose and fix Kafka consumer groups that oscillate between Stable and PreparingRebalance, driven by max.poll.interval.ms timeouts and client-side processing delays.

Kafka controller event queue backing up: overwhelmed controller and stalled metadata

Diagnose and recover when the Kafka controller's event queue backs up, stalling leader elections and metadata propagation.

Kafka fetch request latency high: FetchConsumer vs FetchFollower and page cache misses

Diagnose elevated Kafka fetch request latency by distinguishing consumer fetches from replica fetches and identifying page cache misses as the root cause.

Kafka ISR shrinking: IsrShrinksPerSec, flapping, and the cascade to offline

Diagnose ISR shrink storms, flapping replicas, and the cascade to offline partitions in Kafka production clusters.

Kafka KRaft quorum has no leader: current-leader = -1 and frozen metadata

Diagnose and recover a KRaft quorum that has lost its leader when current-leader drops to -1 and metadata updates freeze.

Kafka LEADER_NOT_AVAILABLE: causes during elections, restarts, and topic creation

Diagnose transient and persistent Kafka LEADER_NOT_AVAILABLE errors by correlating leader elections, controller health, ISR state, and offline partitions.

Kafka log compaction falling behind: the dead cleaner thread and unbounded disk growth

Diagnose and fix silent Kafka log cleaner thread crashes that cause compacted topics like __consumer_offsets to grow without bound.

Kafka Log directory failed / OfflineLogDirectoryCount > 0: disk errors and JBOD recovery

Troubleshoot Kafka brokers with offline log directories due to disk I/O errors, JBOD failures, and recover partition availability without data loss.

Kafka NetworkProcessorAvgIdlePercent low: network thread saturation and TLS overhead

Diagnose and fix low NetworkProcessorAvgIdlePercent in Kafka, including network thread saturation from TLS handshakes, connection storms, and large fetch responses.

Kafka NOT_LEADER_FOR_PARTITION: stale metadata, controller lag, and client retries

Diagnose persistent NOT_LEADER_FOR_PARTITION errors by distinguishing transient leader elections from controller event queue backup and broker metadata desync.

Kafka NotEnoughReplicasException: acks=all writes rejected below min.insync.replicas

Diagnose and fix Kafka NotEnoughReplicasException when acks=all writes fail because the ISR shrank below min.insync.replicas.

Kafka OffsetOutOfRangeException: when retention deletes data before the consumer reads it

Fix and prevent Kafka OffsetOutOfRangeException when consumer lag outruns log retention, causing data loss or forced offset resets.

Kafka RecordTooLargeException / MESSAGE_TOO_LARGE: message size limits across the path

Fix Kafka message-size rejections by aligning producer, broker, topic, replica, and consumer limits end to end.

Kafka replica MaxLag growing: slow followers and replica fetcher health

Diagnose and fix growing Kafka replica fetcher lag before it triggers ISR shrinks and write rejections.

Kafka Too many open files: file descriptor exhaustion from segments and connections

Diagnose and fix Kafka broker file descriptor exhaustion caused by log segments and network connections, including quick checks, fixes, and prevention.

Kafka UnderReplicatedPartitions > 0: the most important metric and how to clear it

Troubleshoot and clear Kafka under-replicated partitions by identifying lagging followers, correlating disk, network, and GC signals, and applying the right fix without causing further ISR shrink.

Kubernetes Operations Guides 16 pages

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Kubernetes API Server Rate Limited: How To Fix It

Diagnose and fix API Priority and Fairness starvation in Kubernetes where low-priority traffic blocks critical control plane requests.

Kubernetes conntrack exhaustion: dropped connections under load

Diagnose and resolve Linux nf_conntrack table exhaustion on Kubernetes nodes that causes silent connection drops under load.

Kubernetes Controller-Manager Leader Election Failures

Diagnose lease renewal failures, leaderless windows, and controller reconciliation stalls in the kube-controller-manager.

Kubernetes eviction cascade: when one node failure takes down the cluster

Diagnose and stop node-pressure eviction cascades caused by scheduler overplacement, cgroup v2 accounting changes, and missing hysteresis in Kubernetes clusters.

Kubernetes kube-proxy iptables sync stall: causes and recovery

Diagnose and recover from kube-proxy iptables synchronization stalls caused by xtables lock contention, rule bloat, and restore failures.

Kubernetes kubelet not responding: PLEG, runtime, and certificate issues

Diagnose and fix Kubernetes kubelet failures caused by PLEG stalls, container runtime disconnections, and certificate expiration before nodes go NotReady.

Kubernetes PLEG is not healthy: runtime stalls and node degradation

Diagnose and recover from kubelet PLEG unhealthy errors that cause nodes to go NotReady due to container runtime stalls and serial bottlenecks.

Kubernetes pod CrashLoopBackOff: causes, diagnosis, and fixes

Practical troubleshooting guide for Kubernetes CrashLoopBackOff: identify root causes with kubectl and node signals, apply targeted fixes, and prevent recurrence.

Kubernetes pod creation fails: admission, quota, and CRI errors

Diagnose and fix pre-scheduling pod creation failures caused by admission webhooks, ResourceQuota limits, Pod Security Standards, and CRI image pull errors.

Kubernetes pod Evicted: detection, root cause, and prevention

Detect, diagnose, and prevent Kubernetes pod eviction caused by node memory, disk, inode, and PID pressure.

Kubernetes pod exits immediately: how to diagnose it

Diagnose why a Kubernetes pod exits immediately on first run by reading exit codes, termination reasons, and logs before any restart occurs.

Kubernetes pod ImagePullBackOff: registry, auth, and network diagnosis

Diagnose and resolve Kubernetes ImagePullBackOff errors caused by registry authentication, network issues, and image reference problems.

Kubernetes pod stuck ContainerCreating: volume, network, and image issues

Diagnose and fix Kubernetes pods stuck in ContainerCreating caused by volume mount deadlocks, CNI failures, and image pull problems.

Kubernetes pod stuck Pending: scheduling failures explained

Diagnose why Kubernetes pods remain Pending due to scheduler constraints, resource exhaustion, affinity rules, taints, and volume binding issues.

Kubernetes PVC stuck Pending: storage class, provisioner, and quota

Diagnose and fix PersistentVolumeClaims stuck in Pending due to StorageClass, provisioner, or quota issues.

Kubernetes Scheduler Not Scheduling Pods: Queue Depth & Failure Reasons

Diagnose why Kubernetes pods are stuck pending by reading scheduler queue metrics, plugin rejection reasons, and control plane latency signals.

Microsoft SQL Server Operations Guides 11 pages

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SQL Server CPU utilization high: telling query load apart from a bad plan

SQL Server at 100% CPU is not automatically an incident. Learn how to split SQL Server CPU from other-process CPU, tell legitimate load from a bad plan, and alert on the signals that actually matter.

SQL Server CXPACKET and CXCONSUMER waits: parallelism, MAXDOP, and what is actually wrong

How to read CXPACKET and CXCONSUMER wait stats in SQL Server, when high values are normal, and how to fix the real causes: skewed parallel work, missing indexes, and bad MAXDOP or cost threshold defaults.

SQL Server database in SUSPECT or RECOVERY_PENDING: an offline database and how to recover it

Diagnose and recover a SQL Server database stuck in SUSPECT, RECOVERY_PENDING, or EMERGENCY without jumping straight to data-loss repair.

SQL Server Error 1205: transaction was deadlocked and chosen as the deadlock victim

Diagnose SQL Server deadlocks: capture the xml_deadlock_report, identify the victim, and fix the root cause.

SQL Server Error 18456: login failed for user, and what the state code means

How to read the real cause of SQL Server login failures from the state code in the error log, and what to do about each state.

SQL Server Error 823 and 824: I/O and logical consistency errors

Triage SQL Server severity-24 I/O errors: hard OS-level failures (823), logical consistency and checksum errors (824), and the 825 read-retry canary, plus DBCC CHECKDB, suspect_pages, and restore-first response.

SQL Server Error 9002: the transaction log for the database is full

Diagnose and fix SQL Server error 9002 by reading log_reuse_wait_desc first, then resolving the specific blocker: log backups, open transactions, AG lag, or replication.

SQL Server instance down: no response on port 1433 and where to look first

Triage a SQL Server instance that fails connectivity probes on port 1433 by separating true service outages from worker exhaustion, listener misconfiguration, and database-scoped failures.

SQL Server RESOURCE_SEMAPHORE waits: queries stuck waiting for a memory grant

Diagnose and fix SQL Server RESOURCE_SEMAPHORE waits: what a memory grant queue means, how to find the hoarder, and when to page.

SQL Server TempDB full: the shared scratch database that halts every query

Troubleshoot a full TempDB on SQL Server: find which consumer (user objects, internal spills, version store) is eating space, stop the bleeding, and prevent recurrence.

SQL Server THREADPOOL waits: worker thread exhaustion and refused connections

How to diagnose and resolve SQL Server THREADPOOL waits when worker thread exhaustion makes the instance refuse connections while CPU and I/O sit idle.

MongoDB Operations Guides 23 pages

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MongoDB Application Thread Evictions: How To Fix

Diagnose and fix WiredTiger cache eviction stalls when MongoDB application threads start evicting pages, causing sudden latency spikes.

MongoDB Balancer Stuck On Jumbo Chunks: Fix It

Diagnose and fix permanent shard imbalance in MongoDB caused by a stuck balancer or jumbo chunks that cannot migrate.

MongoDB checkpoint duration climbing: diagnosing slow WiredTiger checkpoints

Diagnose and fix climbing WiredTiger checkpoint duration before it exceeds the 60-second interval and freezes writes.

MongoDB checkpoint stall write freeze: when all writes stop with no error

Troubleshoot the WiredTiger checkpoint stall that silently blocks all MongoDB writes with no errors, leaving reads partially functional.

MongoDB connection churn: high totalCreated rate and thread creation overhead

Diagnose and fix MongoDB connection churn where a climbing totalCreated delta with stable current connections drives thread creation overhead and latency.

MongoDB connection refused at maxIncomingConnections: hitting the connection ceiling

Diagnose and resolve MongoDB connection refusals when inbound connections hit the maxIncomingConnections ceiling or OS file descriptor limits.

MongoDB connection storm spiral: reconnection floods after an election or deploy

Diagnose and break MongoDB connection storm spirals caused by elections, deploys, or network blips. Recognize RSS spikes, ticket contention, and totalCreated churn before they crash the node.

MongoDB disk full: emergency recovery when mongod can't write the journal

Emergency triage and recovery steps when MongoDB exhausts disk space and the journal cannot write, including WiredTiger space reclamation and recovery procedures.

MongoDB disk I/O saturation: correlating iostat with WiredTiger signals

Diagnose MongoDB storage bottlenecks by correlating OS disk saturation signals with WiredTiger checkpoint, journal, and cache metrics.

MongoDB exceeded memory limit for $group — aggregation spills and allowDiskUse

Fix MongoDB aggregation pipeline errors when $group or $sort hit the 100MB memory limit, diagnose disk spills, and restructure pipelines for production stability.

MongoDB journal sync latency high: the storage signal that warns 60 seconds early

Detect, diagnose, and fix high WiredTiger journal sync latency in MongoDB before it stalls j:true and w:majority writes.

MongoDB lock wait times: collection and metadata lock contention during DDL

Diagnose and fix high MongoDB collection and metadata lock wait times caused by DDL operations such as createIndex, dropIndex, and collMod.

MongoDB long-running operations: finding and killing the query holding a ticket

Find and terminate long-running MongoDB operations that are blocking others by holding WiredTiger tickets, using currentOp, killOp, and related diagnostic signals.

MongoDB no primary / election storm: repeated elections and write outages

Diagnose and stop MongoDB replica set election storms where primaries repeatedly step down, causing rolling 2-12 second write outages.

MongoDB not master error: writes hitting a non-primary node after failover

Troubleshoot and fix MongoDB NotWritablePrimary errors that occur when applications write to a non-primary node after failover or election.

MongoDB operation exceeded time limit (MaxTimeMSExpired): maxTimeMS and killed operations

Diagnose MongoDB MaxTimeMSExpired errors. Understand why maxTimeMS kills operations, how to distinguish server-side timeouts from client socket timeouts, and how to find root causes with currentOp and the slow query log.

MongoDB oplog window collapse: secondaries falling off and forced full resync

Diagnose and fix MongoDB oplog window collapse when write surges shrink the replication window and force secondaries into RECOVERING state.

MongoDB RSS growing without cache growth: leaks, threads, and tcmalloc fragmentation

Diagnose why MongoDB resident memory grows while WiredTiger cache stays flat. Covers tcmalloc fragmentation, connection thread stacks, cursor leaks, and version-specific allocator changes.

MongoDB silent index regression: when a dropped index quietly becomes a collection scan

Diagnose and fix the failure mode where MongoDB queries silently switch to collection scans after an index drop or planner regression, causing read latency to grow with collection size.

MongoDB slow query COLLSCAN: collection scans and the missing index

Diagnose and fix MongoDB collection scans (COLLSCAN) that cause slow queries by identifying missing indexes, query plan regressions, and inefficient predicates.

MongoDB ticket exhaustion: WiredTiger read/write tickets and queued operations

Diagnose and fix MongoDB WiredTiger ticket exhaustion when read or write tickets approach zero and operations queue.

MongoDB too stale to catch up: secondary stuck in RECOVERING and how to resync

Diagnose and recover a MongoDB secondary that has fallen past the primary's oplog window, is stuck in RECOVERING, and requires a full initial sync.

MongoDB WiredTiger cache pressure cascade: eviction stalls and latency spikes

Diagnose and break the MongoDB WiredTiger cache pressure cascade before eviction stalls and latency spikes bring down your replica set.

MySQL Operations Guides 23 pages

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MySQL Aborted Connections: Causes And Fixes

Diagnose rising MySQL Aborted_connects and Aborted_clients counters. Distinguish handshake failures from dropped connections, find the root cause, and fix it without restarting the server.

MySQL connection exhaustion: detection, diagnosis, and prevention

Detect, diagnose, and prevent MySQL connection exhaustion before application errors cascade into an outage.

MySQL ERROR 1040 (HY000): Too many connections - causes and fixes

Troubleshoot MySQL ERROR 1040 (HY000) by distinguishing connection leaks from genuine overload, using Threads_running, Threads_connected, and Connection_errors_max_connections.

MySQL ERROR 1045 (28000): Access denied for user - diagnosis

Diagnose MySQL ERROR 1045 (28000) caused by credential mismatches, user@host restrictions, authentication plugin incompatibility, and host cache blocking.

MySQL ERROR 1205: Lock wait timeout exceeded; try restarting transaction

Diagnose and fix MySQL ER_LOCK_WAIT_TIMEOUT. Find blocking transactions, understand statement-level rollback, and prevent row lock contention in production.

MySQL ERROR 1213: Deadlock found when trying to get lock; try restarting transaction

Diagnose and resolve MySQL ERROR 1213 deadlocks in InnoDB. Covers victim selection, gap-lock interaction, diagnostic commands, and prevention.

MySQL ERROR 2006/2013: MySQL server has gone away -- causes and fixes

Troubleshoot MySQL ERROR 2006 and 2013 by distinguishing idle timeout closures from crashes, packet limits, and network timeouts.

MySQL full table scans: Handler_read_rnd_next and the missing index

Diagnose unexpected full table scans in MySQL by correlating Handler_read_rnd_next step-changes with Slow_queries, then isolate the offending query and fix the index coverage.

MySQL Got error 28 from storage engine / No space left on device — recovery

Recover from MySQL errno 28 disk-full conditions by identifying whether binlogs, redo logs, tmpdir, or relay logs consumed the space, and apply the right fix without causing data loss.

MySQL InnoDB history list length growing: purge lag explained

Understand how InnoDB purge lag works, why the history list length grows, and how MVCC read views turn a single idle transaction into fleet-wide slowdown.

MySQL InnoDB redo log checkpoint stall: when all writes freeze

Diagnose and fix InnoDB redo log checkpoint stalls that synchronously freeze all MySQL writes when checkpoint age exceeds redo capacity.

MySQL InnoDB row lock contention: finding who blocks whom

Diagnose InnoDB row lock contention in MySQL 8.0+ and 5.7 by mapping blocking transactions with performance_schema.data_lock_waits, sys.innodb_lock_waits, and the right status metrics.

MySQL Innodb_buffer_pool_wait_free > 0: buffer pool memory pressure

Diagnose and fix InnoDB buffer pool memory pressure when Innodb_buffer_pool_wait_free climbs above zero.

MySQL long-running transactions: detecting and killing the silent blocker

Detect, diagnose, and kill idle InnoDB transactions that silently hold locks and block purge, causing lock waits and history list growth.

MySQL metadata lock cascade: how one ALTER TABLE freezes a whole table

Diagnose and break a metadata lock cascade when DDL blocks behind a long transaction and connection pools fill with waiting DML.

MySQL online DDL still blocking: ALGORITHM, LOCK, and the copy phase

Why MySQL online DDL still blocks despite ALGORITHM=INPLACE/INSTANT and LOCK=NONE, and how metadata locks cause copy-phase stalls.

MySQL purge lag from an idle transaction: the slow bleed

Diagnose and fix InnoDB purge lag caused by a single idle transaction holding an MVCC read view, leading to unbounded history list growth and gradual query degradation.

MySQL query plan regression: when a query gets slow after a deploy or ANALYZE

Diagnose and fix sudden MySQL query slowdowns caused by bad execution plans after deployments, ANALYZE TABLE, schema changes, or upgrades.

MySQL Replica_IO_Running / Replica_SQL_Running not Yes: replication stopped

Diagnose why MySQL replication I/O or SQL threads stop, read SHOW REPLICA STATUS errors, and recover safely.

MySQL replication lag spiral: Seconds_Behind_Source growing without bound

Diagnose and stop a MySQL replication lag death spiral when the replica cannot keep up, relay logs grow, and Seconds_Behind_Source increases monotonically.

MySQL slow commits with idle CPU: redo and binlog fsync pressure

Diagnose and fix MySQL commit latency when CPU is idle but transactions stall on redo log and binary log fsync pressure.

MySQL slow queries: from Slow_queries to the slow log to the fix

Diagnose MySQL slow queries when Slow_queries climbs, the slow log is disabled, or long_query_time hides real problems. Read-only checks, ratio analysis, and targeted fixes.

MySQL Waiting for table metadata lock: diagnosing the DDL stall

Diagnose MySQL sessions stuck in Waiting for table metadata lock, identify the blocking transaction, and break the DDL stall before connection exhaustion.

Network Monitoring Operations Guides 10 pages

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ARP cache staleness: when IP-to-MAC mapping goes bad

Diagnose and fix ARP cache staleness on Linux and Windows, including NUD state transitions, gc_thresh exhaustion, and stale entries after VM or container migration.

BGP flapping: why a peer keeps resetting and how to find the cause

Diagnose and stop BGP session churn by decoding NOTIFICATION codes, correlating control-plane CPU, and identifying MTU black holes.

BGP NOTIFICATION and Cease messages: what each subcode is telling you

A field reference for decoding BGP NOTIFICATION error codes and Cease subcodes in router logs, with operational context for each.

Device control-plane CPU saturation: when SNMP polling causes the spike

Diagnose and resolve network device control-plane CPU spikes caused by SNMP polling storms, overlapping collectors, and expensive MIB walks.

Interface discards with low utilization: diagnosing ifInDiscards/ifOutDiscards

Diagnose packet discards on network interfaces when utilization appears low, including microburst detection, counter semantics, and per-queue drop analysis.

Locating endpoints behind NAT and wireless: the positioning problem

How NAT boundaries and wireless NAT hide endpoint identity from topology engines, and what signals reveal the gap.

NetFlow v9/IPFIX template desync: flows decoded wrong or dropped after a reboot

Diagnose and fix NetFlow v9 or IPFIX template cache desync after an exporter reboot or upgrade that causes flows to be decoded wrong or silently dropped.

SD-WAN tunnel up but degraded: when the control plane lies

Diagnose SD-WAN tunnels where the control plane reports UP but the data plane has packet loss, latency, or silent drops.

SNMP counter rollover: fake traffic spikes from 32-bit counters

Diagnose and fix impossible traffic spikes caused by 32-bit SNMP counter wraps on high-speed interfaces.

SNMP poller falling behind: the polling-storm cascade and how to catch it

How SNMP scheduler fall-behind causes false device-down alerts, and the signals and fixes that stop the cascade.

NGINX Operations Guides 24 pages

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nginx 499 status code: why clients close connections before the response

Diagnose nginx 499 errors where clients abandon requests before the server responds. Learn to distinguish slow upstreams from network drops and load-balancer noise.

NGINX 502 Bad Gateway: Causes And How To Fix It

Diagnose and fix nginx 502 Bad Gateway errors by reading error logs, upstream variables, and connection state. Covers connection refusal, upstream crashes, oversized headers, and DNS resolution failures.

Nginx 503 Service Temporarily Unavailable: Causes & Fixes

Diagnose why nginx returns 503, distinguish rate-limit rejections from upstream outages, and fix the root cause without guessing.

NGINX 504 Gateway Time-Out: Causes & Fixes

Fix nginx 504 Gateway Timeout by isolating slow upstreams, tuning proxy_read_timeout, and distinguishing 504 from 502.

NGINX active connections climbing: reading, writing, waiting explained

Interpret NGINX stub_status Reading, Writing, and Waiting states to distinguish healthy keepalive reuse from slow clients, slow upstreams, and connection exhaustion.

NGINX Backend Cascade Failure: When Slow Upstreams Take Down Everything

Diagnose and fix the cascade failure where one slow upstream exhausts nginx worker connections, overloads healthy backends, and brings down your entire proxy tier.

nginx connect() failed (111: Connection refused) while connecting to upstream

Diagnose and fix nginx error 111 when connecting to upstream backends, including container networking pitfalls, IPv6 mismatches, and firewall blocks.

NGINX Connection Exhaustion: Detection, Diagnosis & Prevention

Detect, diagnose, and prevent NGINX connection exhaustion before it causes cliff-edge timeouts. Covers worker_connections limits, kernel accept queues, keepalive pileup, and upstream slowdown.

NGINX Dropped Connections: The Accepts vs Handled Gap

Diagnose NGINX connection drops by reading the stub_status accepts versus handled gap, a leading indicator of slot and file-descriptor exhaustion.

nginx limiting requests, excess -- understanding limit_req rejections

How nginx's limit_req leaky bucket rate limiting works, why rejected requests return 503 by default, and how to interpret excess rejections in error logs.

NGINX Listen Queue Overflow: Somaxconn, Backlog & Silent Connection Drops

Diagnose and fix kernel-level TCP listen queue overflows that silently drop NGINX connections before they reach worker processes.

nginx no live upstreams while connecting to upstream: what it means

Why nginx logs no live upstreams while connecting to upstream, how passive health checks mark every server unavailable, and how to recover from the 502 cascade.

NGINX proxy_cache not caching: why responses bypass the cache

Troubleshoot why NGINX proxy_cache silently skips caching and serves BYPASS or MISS for responses that should be cached.

NGINX reload not applying config: why old workers keep serving

Diagnose why NGINX configuration reloads fail silently or leave old worker processes serving traffic with stale configuration.

NGINX slow requests: from access log to root cause

Triage elevated NGINX $request_time by isolating client-side delays, upstream latency, temp-file spill, and CPU saturation using access log variables and OS signals.

nginx upstream prematurely closed connection while reading response header

Fix nginx 502 errors caused by upstream closing the connection before response headers are fully read. Diagnose keepalive mismatches, backend crashes, and worker recycling.

nginx upstream sent too big header while reading response header from upstream

Fix the nginx 502 Bad Gateway error that occurs when upstream response headers exceed proxy_buffer_size, common with large cookies, JWTs, and multiple Set-Cookie headers.

nginx upstream timed out (110: Connection timed out) while connecting/reading

Diagnose and fix nginx upstream timeout errors. Learn to distinguish connect, send, and read phases, interpret retry encoding in $upstream_response_time, and tune proxy_next_upstream without causing cascades.

nginx: a client request body is buffered to a temporary file — what it means

Understand why nginx buffers client request bodies to temporary files, how client_body_buffer_size controls the threshold, and when to tune or disable buffering for streaming uploads.

nginx: bind() to 0.0.0.0:80 failed (98: Address already in use)

Diagnose and fix nginx EADDRINUSE errors caused by stale masters, duplicate listen directives, port conflicts, and SO_REUSEPORT misconfigurations.

nginx: configuration file test failed - finding the syntax error

Diagnose and fix nginx configuration syntax errors when nginx -t fails, without disrupting the running server.

nginx: no resolver defined to resolve - dynamic upstream DNS

Fix the nginx 'no resolver defined to resolve' error when using variable-based proxy_pass, and understand dynamic upstream DNS resolution with the resolver directive and the resolve parameter.

Nginx: Too Many Open Files - Diagnosing File Descriptor Exhaustion

Diagnose nginx file descriptor exhaustion when accept4 fails with EMFILE, connections drop silently, and error logging stops.

Nginx: worker_connections Are Not Enough - Causes & Fixes

Diagnose and fix nginx worker_connections exhaustion, including the 2x proxy multiplier, worker_rlimit_nofile limits, and why slow backends are often the real cause.

PostgreSQL Operations Guides 17 pages

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PostgreSQL ALTER TABLE blocked: zero-downtime DDL patterns

Diagnose why ALTER TABLE blocks in PostgreSQL, break lock cascades, and apply safe DDL patterns that avoid ACCESS EXCLUSIVE outages.

PostgreSQL autovacuum blocked by long-running transaction: detection and fix

Detect when long-running transactions, replication slots, or standby feedback pin the PostgreSQL xmin horizon and block autovacuum from reclaiming dead tuples.

PostgreSQL autovacuum not running: detection, causes, and fixes

Detect when PostgreSQL autovacuum is blocked or misconfigured, diagnose the root cause, and fix it before bloat and XID wraparound force an outage.

PostgreSQL checkpoint storms: detection, causes, and tuning

Detect and fix PostgreSQL checkpoint storms before they stall your queries. Covers forced vs timed checkpoints, max_wal_size tuning, and safe tuning tradeoffs.

PostgreSQL Connection Exhaustion: Detection, Diagnosis & Prevention

Detect, diagnose, and prevent PostgreSQL connection exhaustion caused by pool leaks, idle-in-transaction sessions, and missing connection limits.

PostgreSQL connection refused: pg_hba, listen_addresses, and TCP diagnosis

Diagnose PostgreSQL connection refused errors by distinguishing network-layer bind failures, firewall drops, and pg_hba.conf authentication rejections.

PostgreSQL deadlock detected: how to diagnose and prevent deadlocks

Diagnose PostgreSQL deadlocks, read wait-for graphs, fix inverted lock ordering, and prevent recurrence with log_lock_waits and SKIP LOCKED.

PostgreSQL disk full: emergency recovery and root cause analysis

Emergency runbook for PostgreSQL disk-full incidents. Diagnose WAL accumulation, replication slots, temp files, and table bloat without guessing.

PostgreSQL ERROR: Could Not Obtain Lock — Diagnosis & Recovery

Diagnose and recover from PostgreSQL lock contention errors, including NOWAIT failures, lock timeout cancellations, and DDL blocking locks.

PostgreSQL FATAL: Too Many Connections - Causes & Fixes

Diagnose and resolve PostgreSQL connection exhaustion. Covers max_connections, idle-in-transaction, PgBouncer pooling, and superuser reserved connections.

PostgreSQL Idle In Transaction: Detecting & Killing Zombie Sessions

Detect and terminate PostgreSQL sessions stuck in idle in transaction before they block VACUUM, trigger bloat, and exhaust connections.

PostgreSQL index bloat: detection and REINDEX CONCURRENTLY recovery

Detect B-tree index bloat in PostgreSQL using pgstatindex and recover online with REINDEX CONCURRENTLY without locking the table.

PostgreSQL logical replication failures: conflicts, schema drift, and recovery

Diagnose and resolve PostgreSQL logical replication failures including subscriber conflicts, schema drift gaps, replica identity misconfiguration, and recovery procedures.

PostgreSQL Slow Queries: Diagnosis From Log To Plan To Fix

A practical troubleshooting guide for diagnosing PostgreSQL slow queries using pg_stat_statements, log_min_duration_statement, auto_explain, and execution plan analysis.

PostgreSQL transaction ID wraparound: detection and emergency recovery

Detect transaction ID wraparound before it halts writes, then recover safely with VACUUM FREEZE.

PostgreSQL: checkpoints are occurring too frequently -- what to tune

Diagnose and fix frequent PostgreSQL checkpoints. Learn when to raise max_wal_size, adjust checkpoint_timeout, and spread I/O with checkpoint_completion_target.

PostgreSQL: database is not accepting commands to avoid wraparound data loss

Recover from PostgreSQL's transaction ID wraparound shutdown. Learn why writes are blocked, how to clear blockers, and the correct VACUUM procedure for modern versions.

RabbitMQ Operations Guides 12 pages

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RabbitMQ ACCESS_REFUSED - Login was refused: authentication failures and credential rotation

Diagnose RabbitMQ 'ACCESS_REFUSED - Login was refused using authentication mechanism PLAIN' errors: stale credentials after rotation, disabled users, guest-from-remote, LDAP backend failures, and brute-force floods, plus how to stop the reconnect churn they cause.

RabbitMQ connection blocked / blocking: publishers frozen by a resource alarm

Why RabbitMQ connections enter the blocking or blocked state, how to tell it apart from flow control, and how to unblock publishers frozen by a memory or disk resource alarm.

RabbitMQ connection in flow state: credit-based backpressure explained

What RabbitMQ's per-connection flow state actually means, how credit-based backpressure works inside the broker, and when sustained flow is a real write-path bottleneck.

RabbitMQ connection storm: reconnect loops, FD pressure, and CPU spent on handshakes

Diagnose and stop a RabbitMQ connection storm: reconnect loops driving churn, file descriptor and socket pressure, and Erlang scheduler CPU burned on connection handshakes.

RabbitMQ consumer timeout: delivery acknowledgement timed out and the channel is closed

Why RabbitMQ closes channels with 'delivery acknowledgement timed out', how the consumer_timeout mechanism works, and how to diagnose and fix slow or stuck consumers.

RabbitMQ consumers connected but not acknowledging: the consumer black hole

RabbitMQ shows consumers attached but ack rate is zero and messages_ready is rising. How to diagnose stuck consumers, zombie connections, and downstream stalls before the memory alarm fires.

RabbitMQ messages lost on restart: durable queues, persistent messages, and transient traps

Why RabbitMQ messages disappear after a broker restart: the durable queue plus persistent message requirement, transient traps, and the classic queue fsync gap.

RabbitMQ network partition detected: split-brain in cluster_status

What the Network Partitions section of rabbitmqctl cluster_status means, how to confirm a real split versus a false positive, and how to respond without making data divergence worse.

RabbitMQ node down: telling a dead broker apart from a partitioned one

How to distinguish a genuinely dead RabbitMQ node from a network-partitioned one, using the running field, partitions array, cluster link traffic, and the quorum-critical check.

RabbitMQ NOT_FOUND - no queue or exchange: publishing to something that does not exist

Why RabbitMQ closes your channel with 404 NOT_FOUND when you publish to or consume from an exchange or queue that does not exist, how to find what is missing, and how to stop it recurring after deploys.

RabbitMQ PRECONDITION_FAILED - inequivalent arg: redeclaring a queue with different properties

Why RabbitMQ closes the channel with 406 PRECONDITION_FAILED when a client redeclares a queue or exchange with different arguments, and how to reconcile it safely.

RabbitMQ RESOURCE_LOCKED - cannot obtain exclusive access to queue

Diagnose and fix RabbitMQ channel error 405 RESOURCE_LOCKED when a second connection tries to use an exclusive queue still owned by another connection.

Redis Operations Guides 24 pages

Open the Redis Operations Guides hub

MISCONF Redis is configured to save RDB snapshots - what it means and how to fix it

Fix the Redis MISCONF error that blocks writes when a background RDB save fails. Diagnose root causes, recover safely, and understand the stop-writes-on-bgsave-error guard.

Redis aof_last_write_status:err: AOF write failures and recovery

Diagnose and recover when Redis AOF writes fail, including disk full, I/O errors, and the path from aof_last_write_status:err back to ok.

Redis big keys: finding the giant key that blocks the event loop

Diagnose and fix Redis latency caused by oversized keys and O(N) commands blocking the single-threaded event loop.

Redis BUSY Redis is busy running a script: blocking Lua and how to recover

Troubleshoot the Redis BUSY error from long-running Lua scripts. Learn how SCRIPT KILL, SHUTDOWN NOSAVE, and lua-time-limit work, and how to prevent event-loop blocking.

Redis Can't save in background: fork: Cannot allocate memory - diagnosis and fix

Why Redis background saves fail with fork: Cannot allocate memory, how to diagnose vm.overcommit_memory and COW pressure, and how to fix it without restarting Redis.

Redis client output buffer overflow: slow consumers and client-output-buffer-limit

Diagnose and fix Redis client output buffer overflow from slow consumers, including omem analysis, client-output-buffer-limit tuning, and MONITOR detection.

Redis cluster_slots_pfail > 0: impending node failure in a cluster

Investigate Redis Cluster PFAIL before it escalates to FAIL. Learn the gossip mechanism, quorum rules, zombie states, and how to distinguish transient pauses from real node failure.

Redis CLUSTERDOWN / cluster_state:fail: slot coverage and recovery

Diagnose and recover when Redis Cluster reports cluster_state:fail or clients see CLUSTERDOWN due to missing hash slot coverage.

Redis connected_clients climbing: connection leak detection

Diagnose and fix a sustained climb in Redis connected_clients when traffic is flat, including CLIENT LIST analysis, timeout configuration, and connection churn detection.

Redis connection exhaustion: leaks, pools, and the retry storm

Diagnose and fix Redis connection exhaustion, from pool misconfiguration and client leaks to retry storms that amplify the outage.

Redis CPU saturation: hitting the single-core throughput ceiling

Diagnose Redis main-thread CPU saturation. Learn why single-threaded command execution creates a linear latency ramp, which metrics expose it, and how to relieve the bottleneck.

Redis event loop blocked: when one slow command freezes everything

Diagnose and fix Redis event loop blocking caused by slow commands, Lua scripts, and large key operations.

Redis KEYS command blocking production: why to replace it with SCAN

Diagnose and fix Redis production outages caused by the KEYS command blocking the single-threaded event loop, and replace it with SCAN.

Redis MASTERDOWN / master_link_status:down: replication link broken

Diagnose and fix a Redis replica when master_link_status flips to down, the replication link breaks, and stale reads are served.

Redis max number of clients reached: maxclients and rejected_connections

Diagnose and resolve Redis maxclients exhaustion, rejected_connections spikes, and connection pool leaks with CLIENT LIST, CLIENT KILL, and ulimit tuning.

Redis maxmemory not set: why every production instance needs a memory limit

Running Redis without maxmemory is the most common production misconfiguration. Learn how to size it, pair it with an eviction policy, and avoid OOM kills.

Redis memory pressure spiral: eviction thrashing and how to break it

Diagnose and break the Redis memory pressure spiral where eviction, cache misses, and re-population writes feedback into each other.

Redis OOM command not allowed when used memory > 'maxmemory' - causes and fixes

Troubleshoot Redis write rejections caused by maxmemory exhaustion under noeviction or volatile policies, diagnose silent failures, and fix the root cause without guessing.

Redis OOM-killed by the kernel: RSS, overcommit, and recovery

Why Redis dies to the kernel OOM killer even when used_memory looks healthy, how to diagnose RSS bloat from fragmentation and COW, and how to recover.

Redis rdb_last_bgsave_status:err: diagnosing failed background saves

Diagnose why Redis background saves fail and recover from `rdb_last_bgsave_status:err` without guessing.

Redis READONLY You can't write against a read only replica - causes and fixes

Diagnose and fix the Redis READONLY error when applications write to a replica, including routing bugs, stale topology after failover, and runtime misconfigurations.

Redis replication backlog overflow: full-resync storms and the 1MB default

Diagnose and break replication backlog overflow loops in Redis, where a 1MB default triggers full resync storms that fork the primary and cascade latency to every replica.

Redis replication lag: detection, diagnosis, and fixes

Troubleshoot Redis replication lag by measuring byte-level offsets, identifying resource bottlenecks on replicas, and preventing full resync cascades caused by undersized backlogs.

Redis sync_full incrementing: diagnosing full resync events

Diagnose why Redis sync_full counters are climbing, identify replication backlog exhaustion, and stop full resync storms before they overwhelm the primary.

VMware vSphere Operations Guides 5 pages

Open the VMware vSphere Operations Guides hub

vCenter certificate expired: the STS signing cert outage nobody saw coming

Diagnose and recover from an expired STS signing certificate that takes down all vCenter authentication at once.

vCenter vpxd crash loop: the core service that keeps restarting

Operator reference for diagnosing and stopping vCenter vpxd crash loops, including heap exhaustion, ContainerView leaks, certificate expiry, and version-specific bugs.

vSphere CPU limit hit (%MLMTD): the forgotten MHz cap that silently throttles a VM

How to diagnose and fix CPU limit throttling (%MLMTD) in vSphere, where a set-and-forgotten MHz cap silently degrades VMs that look healthy on ready time.

vSphere HA 'Insufficient resources to satisfy configured failover level': admission control

Why vSphere HA blocks power-ons and vMotions with the failover level error, how admission control policies work, and how to fix it without losing the restart guarantee.

vSphere PSOD (purple screen of death): diagnosing an ESXi host crash

How to diagnose an ESXi purple screen of death: read the diagnostic screen, preserve the core dump, and correlate hardware and driver signals before the host reboots.

Apache ZooKeeper Operations Guides 16 pages

Open the Apache ZooKeeper Operations Guides hub

ZooKeeper "Cannot open channel to N at election address": the blocked election port

Diagnose the asymmetric connectivity trap where a blocked 3888 leader election port stays invisible until the next leader election kills the ensemble.

ZooKeeper "Client session timed out, have not heard from server": the heartbeat miss

Why the ZooKeeper client logs a session timeout heartbeat miss, what it means for the session, and how to isolate server GC, client GC, or network as the root cause.

ZooKeeper "Detected pause in JVM or host machine (eg GC)": the pause-monitor warning

Operator reference for ZooKeeper's JvmPauseMonitor warning: how to distinguish Stop-the-World GC from host-level freezes and which signals to correlate during recovery.

ZooKeeper "Packet len is out of range": jute.maxbuffer and oversized znodes

Diagnose and fix ZooKeeper's jute.maxbuffer rejection, from oversized znode blobs to huge getChildren responses blocking follower sync.

ZooKeeper "Too many connections from /IP - max is 60": maxClientCnxns rejecting clients

Diagnose ZooKeeper maxClientCnxns rejections: why the per-IP limit silently denies clients behind NAT and how to catch it with zk_connection_rejected.

ZooKeeper "Unable to load database on disk": corrupt snapshot on startup

Why a ZooKeeper node refuses to start with Unable to load database on disk, how to triage the corrupt file, and how to recover without losing the ensemble.

ZooKeeper "X is not executed because it is not in the whitelist": four-letter-word commands blocked

Why ZooKeeper 3.5.3+ blocks four-letter-word commands by default and how to restore monitoring visibility without re-introducing the DoS surface.

ZooKeeper autopurge not configured: snapshots and logs filling the disk over months

Diagnose and fix ZooKeeper disk exhaustion caused by disabled autopurge, with safe checks for snapshot and transaction log accumulation.

ZooKeeper avg_latency hides write stalls: why the headline number lies

Why zk_avg_latency hides write stalls on read-heavy ensembles, and how to monitor zk_updatelatency and zk_readlatency separately to catch them.

ZooKeeper data tree digest mismatch: detecting corruption before it spreads

What zk_digest_mismatches_count means, the four causes to investigate first, and how to triage single-node corruption from a ZAB replication bug.

ZooKeeper KeeperErrorCode = ConnectionLoss: the transient disconnect every client hits

What ConnectionLoss actually means, how to tell it from SessionExpired, and how to diagnose a storm of disconnects across clients.

ZooKeeper KeeperErrorCode = NoAuth: ACL denials on protected znodes

Diagnose and resolve ZooKeeper KeeperErrorCode = NoAuth errors from missing addAuthInfo calls, digest and SASL credential mismatches, and the 3.9.2 exists() ACL change.

ZooKeeper KeeperErrorCode = NoNode: operating on a path that doesn't exist

Triage ZooKeeper NoNode errors: separate application bugs from session-expiration cascades with read-only checks and mntr signals.

ZooKeeper KeeperErrorCode = Session expired: ephemeral nodes gone, clients evicted

Diagnose ZooKeeper session expiration, its cascading effects on ephemeral nodes and watches, and the GC, network, and failover causes behind mass client eviction.

ZooKeeper quorum loss: no leader elected and every write is failing

Recover from ZooKeeper quorum loss: confirm no leader is elected, identify the cause, and restore enough voting members to form quorum without losing data.

ZooKeeper transaction log disk full: the crash with no graceful degradation

Diagnose and recover from a full ZooKeeper dataLogDir partition, including the crash-loop and silent data loss variants, plus the disk headroom rules that prevent recurrence.

Academy

Elasticsearch Yellow Cluster: Unassigned Shards Fix

A guide to resolving the common Elasticsearch yellow state by investigating shard allocation- understanding master election- and preventing data divergence

Consul Service Discovery Failures: Causes & Fixes

Unravel common errors in Consul cluster formation- service registration- and DNS to ensure a highly available service mesh and reliable discovery

Fix NGINX 502/504 Double-Proxy Errors With CloudFront

A systematic guide to diagnosing connection issues between the Cloudflare edge and your NGINX origin server

SSL/TLS Handshake Failures Causing NGINX 502 Errors

A deep dive into diagnosing and resolving the notorious SSL_do_handshake_failed error when proxying traffic with NGINX

Real-World PostgreSQL Deadlock Examples & Fixes

From classic update order conflicts to subtle index contention- learn from real production incidents and their fixes

Fix NGINX 503 Errors From Misconfigured limit_req

A deep dive into tuning NGINX rate limits to protect your origin without accidentally rejecting legitimate users

Tune NGINX Timeouts: Eliminate Upstream Errors

A practical guide to diagnosing and fixing NGINX 502 and 504 errors by configuring the right timeout directives for your backend services

Linux Load Average Spikes: IO Wait & Bottlenecks

Learn to interpret load average correctly and use tools like iostat and vmstat to find the root cause of system performance issues

Kubernetes CrashLoopBackOff: Causes & Quick Fixes

A practical guide to diagnosing and fixing the dreaded Kubernetes pod restart loop- from probe failures to OOMKilled errors

Jenkins Declarative Pipeline: Parallelism Fixes

A guide to mastering the parallel step without deadlocking your agents or running tests on the wrong nodes

Buffering keepalive and Hidden 500-Series Errors in NGINX

A deep dive into nginx buffering keepalive timeouts and how they can silently trigger 500 502 and 504 errors in your infrastructure

Fix Helm Chart Rollback & Pending-Upgrade Failures

A step-by-step playbook to diagnose and resolve stuck Helm releases- from failed hooks to corrupted release secrets

Fix NGINX 502 Bad Gateway In Kubernetes Ingress

Uncover the root causes of upstream errors in Kubernetes- from Ingress controller timeouts to misconfigured readiness probes that silently take your services offline

Docker Compose Networking: Service Discovery & Ports

A guide to debugging inter-container communication, resolving port binding errors, and understanding Docker's internal DNS for seamless service discovery

Apache mod_rewrite Debugging & Log Analysis

A step-by-step guide to using the RewriteLog for troubleshooting complex URL rewriting rules and preventing infinite redirect loops in Apache

AWS ELB 5xx Surge Analysis: Health & Draining

A deep dive into diagnosing ALB 502, 503, and 504 errors by analyzing target health checks, connection timeouts, and session stickiness

25 NGINX Directives to Audit Before Opening a Support Ticket

A practical checklist to help you find and fix common NGINX issues yourself

How To Find And Fix Memory Leaks in C or C++

A practical guide to C and C++ memory management- from manual detection to modern tools and best practices

How To Fix Packet Loss - A Step-by-Step Guide To Reduce It

Your definitive guide to diagnosing, troubleshooting, and fixing frustrating packet loss issues

High CPU Usage Detected How To Fix CPU Overload

A step-by-step guide for developers and SREs to troubleshoot and resolve CPU performance bottlenecks

Effective Strategies for Managing PostgreSQL Deadlocks

Best Practices and Techniques to Prevent and Resolve Deadlocks in PostgreSQL

How To Fix 504 Gateway Timeout Errors In NGINX

A Comprehensive Guide For DevOps & SRE Professionals

How to Troubleshoot Slow Queries in MongoDB

A Beginner’s Guide to Optimizing MongoDB Performance

How To Speed Up Windows 10 & 11: Performance Tips

Essential Tweaks To Boost Your Windows PC

Academy

Browse Netdata webinars and practical learning resources for infrastructure monitoring and troubleshooting.

APC UPS Monitoring

Learn everything about monitoring & troubleshooting APC UPS, what metrics are important to monitor and why, and how to monitor APC UPS with Netdata.

Beanstalk Monitoring

Learn everything about monitoring & troubleshooting Beanstalk, what metrics are important to monitor and why, and how to monitor Beanstalk with Netdata.

BOINC Monitoring

Learn everything about monitoring & troubleshooting BOINC, what metrics are important to monitor and why, and how to monitor BOINC with Netdata.

Ceph Monitoring

Learn everything about monitoring & troubleshooting Ceph, what metrics are important to monitor and why, and how to monitor Ceph with Netdata.

Chrony Monitoring

Learn everything about monitoring & troubleshooting Chrony, what metrics are important to monitor and why, and how to monitor Chrony with Netdata.

ClickHouse Monitoring

Learn everything about monitoring & troubleshooting ClickHouse, what metrics are important to monitor and why, and how to monitor ClickHouse with Netdata.

Elasticsearch Monitoring

Learn everything about monitoring & troubleshooting Elasticsearch, what metrics are important to monitor and why, and how to monitor Elasticsearch with Netdata.

Fail2ban Monitoring

Learn everything about monitoring & troubleshooting Fail2ban, what metrics are important to monitor and why, and how to monitor Fail2ban with Netdata.

Files and Directories Monitoring

Learn everything about monitoring & troubleshooting files and directories, what metrics are important to monitor and why, and how to monitor files and directories with Netdata.

Go-ethereum Monitoring

Learn everything about monitoring & troubleshooting Go-ethereum, what metrics are important to monitor and why, and how to monitor Go-ethereum with Netdata.

Intel GPU Monitoring

Learn everything about monitoring & troubleshooting Intel GPU, what metrics are important to monitor and why, and how to monitor Intel GPU with Netdata.

IPFS Monitoring

Learn everything about monitoring & troubleshooting IPFS, what metrics are important to monitor and why, and how to monitor IPFS with Netdata.

Java Springboot Applications Monitoring

Learn everything you need to know about monitoring & troubleshooting Java Springboot Applications and use Netdata for effective management.

Lighttpd Monitoring

Learn everything about monitoring & troubleshooting Lighttpd, what metrics are important to monitor and why, and how to monitor Lighttpd with Netdata.

Litespeed Monitoring

Learn everything about monitoring & troubleshooting Litespeed, what metrics are important to monitor and why, and how to monitor Litespeed with Netdata.

NTPd Monitoring

Learn everything about monitoring & troubleshooting NTPd, what metrics are important to monitor and why, and how to monitor NTPd with Netdata.

Postfix Monitoring

Learn everything about monitoring & troubleshooting Postfix, what metrics are important to monitor and why, and how to monitor Postfix with Netdata.

PostgreSQL Monitoring

Find out about monitoring & troubleshooting PostgreSQL, what metrics are important to monitor and why, and how to monitor PostgreSQL with Netdata.

RabbitMQ Monitoring

Learn everything about monitoring & troubleshooting RabbitMQ, what metrics are important to monitor and why, and how to monitor RabbitMQ with Netdata.

Squid Monitoring

Learn everything about monitoring & troubleshooting Squid, what metrics are important to monitor and why, and how to monitor Squid with Netdata.

Supervisor Monitoring

Learn everything about monitoring & troubleshooting Supervisor, what metrics are important to monitor and why, and how to monitor Supervisor with Netdata.

YugabyteDB Monitoring

Learn everything about monitoring & troubleshooting YugabyteDB, what metrics are important to monitor and why, and how to monitor YugabyteDB with Netdata.

Case Studies

KAUST Case Study: System Stability For Academia

How KAUST's Systems Research Group Reduced Downtime and Streamlined Troubleshooting with Netdata

Streamlining IT Operations with Netdata

Simplifying Complex Monitoring for a Hybrid Infrastructure

Transforming critical software development

Enhanced observability and real time metric correlation

Case Studies

See how organizations use Netdata to monitor infrastructure, troubleshoot incidents, and operate production systems.

Resources

Webinar: Kubernetes Throttling? It Doesn't Have to Suck!

See how Kubernetes CPU throttling impacts your workloads — and how to monitor, troubleshoot, and fix it. Includes a live stress test of a K8s cluster with real results.

Blog

Introducing Real-Time Conversations with Netdata AI

Your interactive partner for rapid-fire questions, data exploration, and instant analysis.

Save Hours on Troubleshooting with Automated Investigations

Ask Netdata Anything, Get an Expert Analysis in Minutes

Anomaly Rate By Type

Deep Dive into Understanding and Managing Unusual System Behavior

Netdata Assistant: Your AI-Powered Troubleshooting Sidekick

Your Guide to Maximizing Netdata's Capabilities

Understanding System Processes States

Deciphering Process Behavior for Better System Management

Anomaly Rates in the Menu!

Navigating Through Anomalies with Ease for Quicker Troubleshooting

Introducing Netdata Functions (↑ Top)

Extending Monitoring with Customizable Functions

Monitoring & troubleshooting Cassandra with Netdata

Comprehensive Tools for Effective Database Management

7 types of Redis latency and how to fix it

A Game-Changer for DevOps and Developers

Data Collection Strategies For Infrastructure

Tailoring Data Collection for Targeted Troubleshooting and Insights

Troubleshooting Alerts the Right Way: As a Team

Strategies for Effective Alert Management and Resolution

The Netdata Way of Troubleshooting

A Guide to Efficient Problem Solving with Advanced Monitoring

Engineering Team Best Practices For Cloud Monitoring

Live Demonstrations on Solving Common Monitoring Challenges

Root cause analysis using Metric Correlations

Pinpointing Issues Faster with Correlated Insights

Kubernetes monitoring and troubleshooting made simple

Streamlined Solutions for Kubernetes Ecosystems