PostgreSQL Index Metrics Guide - Index Optimization & Management

Index Summary by Database

• What it measures: Provides an overview of index distribution and density across databases and tables.
• Why it matters: Having too many indexes can lead to decreased write performance (slower INSERT, UPDATE, DELETE operations), increased storage usage, query optimization problems as the planner faces more choices, and maintenance challenges for operations like VACUUM and REINDEX.
• Ideal value & Best Practice:
  • Maintain a balanced index-to-table ratio based on actual query patterns
  • Regularly review and justify each index's existence
  • Remove indexes that don't serve critical query patterns
  • Monitor index usage statistics to inform optimization decisions
  • Consider partial indexes instead of full table indexes where appropriate

Unused and Rarely Used Indexes

• What it measures: Identifies indexes that exist but are rarely or never used by queries.
• Why it matters: Unused indexes consume disk space, slow down write operations, and increase system overhead without providing any benefit. They also contribute to longer query planning times due to index bloat.
• Ideal value & Best Practice:
  • Regularly monitor pg_stat_user_indexes to identify unused indexes
  • Remove indexes with zero or minimal usage over significant periods
  • Test index removal in non-production environments first
  • Keep indexes that support critical business operations even if rarely used
  • Implement a regular index maintenance schedule

Duplicate Indexes

• What it measures: Identifies indexes that are identical or nearly identical to other indexes on the same table.
• Why it matters: Duplicate indexes waste disk space, slow down write performance as PostgreSQL must update redundant indexes, and can cause longer query planning times due to excessive index overhead.
• Ideal value & Best Practice:
  • Regularly scan for duplicate indexes using system catalogs
  • Remove redundant indexes while preserving the most efficient one
  • Use CREATE INDEX IF NOT EXISTS to prevent accidental duplicates
  • Document index purposes to avoid creating unnecessary duplicates
  • Consider using composite indexes instead of multiple single-column indexes

Invalid Indexes

• What it measures: Identifies indexes that exist but are not usable by queries due to creation failures or interrupted operations.
• Why it matters: Invalid indexes waste disk space, cannot be used by queries (leading to performance degradation), and may cause issues during REINDEX or CREATE INDEX operations.
• Ideal value & Best Practice:
  • Regularly check for invalid indexes in pg_index
  • Rebuild or drop invalid indexes promptly
  • Use CONCURRENTLY operations during low-traffic periods
  • Monitor index creation jobs for failures or interruptions
  • Implement automated checks for index validity

Index Fragmentation

• What it measures: Monitors the efficiency of B-Tree index leaf nodes and identifies fragmentation issues.
• Why it matters: High fragmentation leads to increased disk I/O, slower index scans, higher storage consumption, and reduced query performance due to sparsely populated index pages from frequent INSERT, UPDATE, and DELETE operations.
• Ideal value & Best Practice:
  • Monitor fragmentation levels regularly
  • Rebuild indexes when fragmentation exceeds 30%
  • Schedule REINDEX operations during maintenance windows
• Consider using pg_repack for minimal locking
  • Balance index maintenance with operational requirements
  • Monitor table modification patterns to predict fragmentation

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