# postgres error: pg_stat_statements must be loaded via shared_preload_libraries - how to enable

## TL;DR

pg_stat_statements needs to be loaded at server start, so CREATE EXTENSION fails until you add it to shared_preload_libraries and restart. Edit postgresql.conf, restart, then CREATE EXTENSION. There is no way to enable it without a restart.

```text
ERROR: pg_stat_statements must be loaded via shared_preload_libraries
```

## Steps

1. Open postgresql.conf and set: shared_preload_libraries = 'pg_stat_statements'.
   Expected: The line is present and uncommented.

2. Restart the Postgres server (reload is not enough; the library loads at postmaster start).
   Expected: The server comes back up with the library preloaded.

3. Create the extension in the database you want stats for: CREATE EXTENSION pg_stat_statements.
   Expected: It creates successfully now.

4. Verify: SELECT count(*) FROM pg_stat_statements.
   Expected: It returns a growing row count as queries run.

5. For managed databases (RDS, Cloud SQL, AlloyDB), enable it through the provider's parameter group or flags page instead of the config file; the restart is still required.
   Expected: Same result, done through the console or CLI.

## When to use

- CREATE EXTENSION pg_stat_statements fails with the preload error
- pg_stat_statements views are empty because the module never loaded
- you are setting up query-level observability on a new instance

## When not to use

- the extension creates but stays empty (check the database you created it in; it is per-database)
- you only need per-session stats (pg_stat_activity may be enough)
- you cannot restart (use auto_explain or log-based capture as a weaker substitute)

## Tool compatibility

- PostgreSQL 12 through 17
- RDS, Cloud SQL, AlloyDB via parameter groups

## Variant phrasings

- "pg_stat_statements shared_preload_libraries restart"
- "must be loaded via shared_preload_libraries fix"
- "enable pg_stat_statements without restart"

## Why it happens

pg_stat_statements hooks into the executor at a level that requires it to be present before any backend starts, which is what shared_preload_libraries does. A plain CREATE EXTENSION loads it too late, so Postgres refuses. The restart is structural, not a bug.

## Edge cases

- adding it to shared_preload_libraries on every node matters for replicas and standby setups too
- pg_stat_statements tracks a bounded number of queries (pg_stat_statements.max); busy servers with many distinct queries evict old entries
- on managed providers the parameter is often named exactly shared_preload_libraries in a custom parameter group

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_v4QsXjKheROA56E3Av-wOQ