Query planner

PostgreSQL Query Optimizer and Planner Behavior

The PostgreSQL optimizer is usually right for the data it can see. When it is wrong, the problem is often stale statistics, skewed values, a misleading predicate, or a query shape that hides selectivity.

Search Topics This Page Covers

postgresql query optimizerpostgres query plannerpostgresql explain analyzepostgresql planner statisticspostgresql plan regression

Signals Worth Watching

Estimated rows are far from actual rows

A nested loop runs thousands of inner scans unexpectedly

A plan changes after a deploy with similar SQL

Prepared statements choose a generic plan that fits nobody well

A filter removes most rows after the expensive scan already happened

Practical PostgreSQL Checks

Compare estimates to actual rows

Bad row estimates explain many bad plans. If actual rows are wildly different, indexes alone may not be the real fix.

EXPLAIN (ANALYZE, BUFFERS, VERBOSE)
SELECT *
FROM orders
WHERE account_id = $1
  AND created_at >= now() - interval '30 days';

Refresh statistics deliberately

Statistics are the optimizer's map. When the map is stale or too coarse, the route can be expensive.

ANALYZE orders;

SELECT attname, n_distinct, most_common_vals
FROM pg_stats
WHERE tablename = 'orders';

How MonPG Helps

MonPG keeps historical query timing so plan regressions are easier to spot after deploys.

Query detail views connect pg_stat_statements, EXPLAIN output, index usage, and buffer behavior.

Alerts can fire when a query family changes shape, not only when the whole database is slow.

Related PostgreSQL Guides

Documentation for This Topic

Hands-on setup, integration, and troubleshooting guides from the MonPG product docs.

Browse all documentation →

PostgreSQL Tools

Related Topic Hubs

Monitor PostgreSQL before tuning turns into firefighting.

MonPG gives teams query history, alerts, index guidance, vacuum visibility, replication signals, and cloud PostgreSQL monitoring in one place.

Start free