PostgreSQL Operations for Application Developers
You don’t need to be a DBA to work effectively with PostgreSQL. Here’s what developers need to know for day-to-day operations. Connection Basics 1 2 3 4 5 6 7 8 9 10 11 12 13 # Connect psql -h localhost -U myuser -d mydb # With password prompt psql -h localhost -U myuser -d mydb -W # Connection string psql "postgresql://user:pass@localhost:5432/mydb" # Common options psql -c "SELECT 1" # Run single command psql -f script.sql # Run file psql -A -t -c "SELECT 1" # Unaligned, tuples only psql Commands \ \ \ \ \ \ \ \ \ \ \ l c d d d d d d x t q t t i u f i d + t m b a i n b n a l g m e e n a m e L C L L D L L L T T Q i o i i e i i i o o u s n s s s s s s g g i t n t t c t t t g g t e r l l d c t t i i u f e e a t a a b n s u t b b e d e n e q a t l l e r c x u b o e e t x s t p e a s s a e / i a r s d b s r o n y e a w l o n d s t i e l s e t a t e d i b h s m a o i s s u n e i t g z p e u s t Essential Queries Table Information 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 -- Table sizes SELECT tablename, pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) AS size FROM pg_tables WHERE schemaname = 'public' ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC; -- Row counts (estimate) SELECT relname AS table, reltuples::bigint AS row_estimate FROM pg_class WHERE relkind = 'r' AND relnamespace = 'public'::regnamespace ORDER BY reltuples DESC; -- Exact row counts (slow on large tables) SELECT 'SELECT ''' || tablename || ''' AS table, COUNT(*) FROM ' || tablename || ' UNION ALL' FROM pg_tables WHERE schemaname = 'public'; Index Information 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -- Index sizes SELECT indexrelname AS index, pg_size_pretty(pg_relation_size(indexrelid)) AS size FROM pg_stat_user_indexes ORDER BY pg_relation_size(indexrelid) DESC; -- Unused indexes SELECT schemaname || '.' || relname AS table, indexrelname AS index, idx_scan AS scans FROM pg_stat_user_indexes WHERE idx_scan = 0 ORDER BY pg_relation_size(indexrelid) DESC; -- Index usage SELECT relname AS table, indexrelname AS index, idx_scan AS scans, idx_tup_read AS tuples_read, idx_tup_fetch AS tuples_fetched FROM pg_stat_user_indexes ORDER BY idx_scan DESC; Active Queries 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 -- Running queries SELECT pid, now() - pg_stat_activity.query_start AS duration, query, state FROM pg_stat_activity WHERE state != 'idle' ORDER BY duration DESC; -- Long-running queries (> 5 minutes) SELECT pid, now() - pg_stat_activity.query_start AS duration, query FROM pg_stat_activity WHERE (now() - pg_stat_activity.query_start) > interval '5 minutes' AND state != 'idle'; -- Kill a query SELECT pg_cancel_backend(pid); -- Graceful SELECT pg_terminate_backend(pid); -- Force Lock Investigation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 -- Blocked queries SELECT blocked_locks.pid AS blocked_pid, blocked_activity.usename AS blocked_user, blocking_locks.pid AS blocking_pid, blocking_activity.usename AS blocking_user, blocked_activity.query AS blocked_query FROM pg_catalog.pg_locks blocked_locks JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid JOIN pg_catalog.pg_locks blocking_locks ON blocking_locks.locktype = blocked_locks.locktype AND blocking_locks.database IS NOT DISTINCT FROM blocked_locks.database AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid AND blocking_locks.pid != blocked_locks.pid JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid WHERE NOT blocked_locks.granted; EXPLAIN ANALYZE 1 2 3 4 5 6 7 8 -- Show query plan with actual timing EXPLAIN ANALYZE SELECT * FROM users WHERE email = 'test@example.com'; -- With buffers (I/O stats) EXPLAIN (ANALYZE, BUFFERS) SELECT * FROM users WHERE email = 'test@example.com'; -- Format as JSON EXPLAIN (ANALYZE, FORMAT JSON) SELECT * FROM users WHERE email = 'test@example.com'; Key things to look for: ...