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FM-KED-002 — PostgreSQL Table and Index Bloat (Missing or Ineffective VACUUM)

Severity: S2 — High
Recovery Class: B — Standard Recovery
Covered by Monthly Support: Yes

Description

PostgreSQL database performance degrades over time due to table and index bloat caused by insufficient or ineffective VACUUM operations.

This issue manifests gradually and is commonly observed on systems with high write activity, long-running transactions, or misconfigured autovacuum settings.

Typical Symptoms

  • Slow queries without obvious query plan changes
  • Increased disk usage on database volumes
  • Tables or indexes significantly larger than expected
  • Elevated I/O usage
  • Application timeouts under normal load

Diagnostic Checklist

Identify Database Size and Largest Tables

SELECT
  relname AS table_name,
  pg_size_pretty(pg_total_relation_size(relid)) AS total_size
FROM pg_catalog.pg_statio_user_tables
ORDER BY pg_total_relation_size(relid) DESC
LIMIT 10;

Check Autovacuum Activity

SELECT
  relname,
  last_vacuum,
  last_autovacuum,
  n_dead_tup
FROM pg_stat_user_tables
ORDER BY n_dead_tup DESC;

Recovery Procedure

Follow steps carefully. Some operations are I/O intensive.

1. Run Manual VACUUM (Non-blocking)

VACUUM (VERBOSE, ANALYZE);

2. Vacuum Specific Tables

VACUUM (VERBOSE, ANALYZE) table_name;

Use when bloat is localized.

3. Reclaim Disk Space (Blocking)

VACUUM FULL table_name;

⚠️ Locks the table for the duration of the operation
⚠️ Use during maintenance windows only

4. Reindex Bloated Indexes

REINDEX TABLE table_name;

Or concurrently, when supported:

REINDEX INDEX CONCURRENTLY index_name;

Preventive Notes

  • Ensure autovacuum is enabled and properly tuned
  • Monitor n_dead_tup growth over time
  • Avoid long-running transactions
  • Schedule periodic maintenance for write-heavy tables

Operational Notes

  • Disk space reclaimed by VACUUM is reusable by PostgreSQL, not always returned to the OS
  • VACUUM FULL physically rewrites tables and should be used sparingly
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