Maintain Table Statistics with VACUUM and ANALYZE

Outdated statistics cause the query planner to make poor decisions. VACUUM reclaims space, ANALYZE updates statistics.

Incorrect (stale statistics):

-- Table has 1M rows but stats say 1000
-- Query planner chooses wrong strategy
explain select * from orders where status = 'pending';
-- Shows: Seq Scan (because stats show small table)
-- Actually: Index Scan would be much faster

Correct (maintain fresh statistics):

-- Manually analyze after large data changes
analyze orders;

-- Analyze specific columns used in WHERE clauses
analyze orders (status, created_at);

-- Check when tables were last analyzed
select
  relname,
  last_vacuum,
  last_autovacuum,
  last_analyze,
  last_autoanalyze
from pg_stat_user_tables
order by last_analyze nulls first;

Autovacuum tuning for busy tables:

-- Increase frequency for high-churn tables
alter table orders set (
  autovacuum_vacuum_scale_factor = 0.05,     -- Vacuum at 5% dead tuples (default 20%)
  autovacuum_analyze_scale_factor = 0.02     -- Analyze at 2% changes (default 10%)
);

-- Check autovacuum status
select * from pg_stat_progress_vacuum;

Reference: VACUUM