PostgreSQL

A successful backup job only proves a file was written. This runbook executes an end-to-end restore and data validation drill in an isolated staging environment.

When a replica falls behind, is the bottleneck in WAL generation, network transport, or replay contention? Pinpoint the exact layer with read-only triage queries.

Three root causes of FATAL: sorry, too many clients already, single diagnostic query to identify the cause, and permanent mitigation via max_connections and PgBouncer.

Four root causes of psql password authentication failed: incorrect password, md5/SCRAM mismatch, pg_hba.conf rule ordering, and port/cluster confusion. Step-by-step triage.

Difference between connection refused, timeout, and no pg_hba entry; triage for listen_addresses, port conflicts, firewalls, and Docker container mappings.

Root cause of duplicate key violations after restore or bulk migration, one-line setval repair, and an automated schema-wide PL/pgSQL DO block.

Why replica queries get cancelled due to recovery conflicts, diagnosis via pg_stat_database_conflicts, and three mitigation strategies.

The relationship of reserved connection slots to max_connections, leveraging the superuser recovery window, and tracking down connection leaks.

Safely terminating active sessions before DROP DATABASE, ALLOW_CONNECTIONS isolation, prepared transactions, and replication slot blockers.

The Docker /dev/shm 64MB default limit, parallel query shared memory exhaustion, proper work_mem calculation, and ordered remediation.

Connection parameters, meta commands (\d, \l, \du), .psqlrc template, COPY streaming, and real-time lock/activity triage queries.

pg_hba.conf hardening rules, SCRAM-SHA-256 password policies, SSL/TLS verify-full, pgaudit audit trails, public schema lockdown, and single-query security check scripts.

Logical backups with pg_dump/pg_dumpall, physical backups with pg_basebackup and pgBackRest, WAL archiving, and Point-in-Time Recovery (PITR) quick reference.

B-Tree, BRIN, GIN, GiST index selection, EXPLAIN (ANALYZE, BUFFERS) node analysis, slow query triage via pg_stat_statements, and index bloat remediation.

Distributed consensus-backed HA topology using etcd and Patroni to eliminate split-brain hazards and guarantee sub-15s automatic failover with HAProxy routing.

Deploy and scale pgvector HNSW safely in production: maintenance_work_mem sizing, WAL throughput, Patroni replication, lock mitigation, hybrid search, and diagnostic queries.

Comprehensive architectural guide on how PostgreSQL shared_buffers and Linux OS page cache interact, buffered I/O execution pipeline, double caching mechanics, cache hit ratio realities, and dual-layer tuning.

Technical guide on PostgreSQL WAL architecture, Full Page Writes (FPW), checkpoint spreading via checkpoint_completion_target, and high-write I/O spike mitigation.

When PostgreSQL approaches the 2-billion transaction horizon, it forces an emergency shutdown to prevent data loss. This deep dive details how to proactively monitor and tune autovacuum to guarantee zero downtime.