first commit

.agents/skills/supabase-postgres-best-practices/references/monitor-vacuum-analyze.md

@@ -0,0 +1,55 @@
+---
+title: Maintain Table Statistics with VACUUM and ANALYZE
+impact: MEDIUM
+impactDescription: 2-10x better query plans with accurate statistics
+tags: vacuum, analyze, statistics, maintenance, autovacuum
+---
+
+## 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+Outdated statistics cause the query planner to make poor decisions.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):**
+
+```sql
+-- 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):**
+
+```sql
+-- 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:
+
+```sql
+-- 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](https://supabase.com/docs/guides/database/database-size#vacuum-operations)