# Query observation

Observe a concrete query through its plan and request metadata. Start by recording the SQL, parameters, data size and expected rows so that a later comparison describes the same task.

## Plans and execution

EXPLAIN QUERY PLAN shows the selected access path without executing the query. EXPLAIN ANALYZE executes the statement and reports measurements. An analyzed write changes data once, so use transaction controls when it should be rolled back.

## Active and finished requests

`system.processes` exposes active requests. `system.query_log` stores configured structured history. A query ID connects request information with the response and diagnostic messages.

Time, memory, result-row and response-byte settings can bound one request. Inspect effective settings when a saved value differs from a server ceiling.

See [query optimization](https://coordinatordb.com/docs/guides/clickhouse/performance-and-monitoring/query-optimization), [query history](https://coordinatordb.com/docs/guides/clickhouse/performance-and-monitoring/diagnose-slow-queries) and [`EXPLAIN`](https://coordinatordb.com/docs/reference/statements/explain).