Reports the number of blocks (pages) that can be stored within a file segment.
At a glance
| Property | Value |
|---|---|
| Parameter | segment_size |
| Category | Preset Options |
| Default | (see documentation) |
| Value type | integer |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 12, 13, 14, 15, 16, 17, 18, 19 (added in 12) |
What it does
Reports the number of blocks (pages) that can be stored within a file segment. It is determined by the value of RELSEG_SIZE when building the server. The maximum size of a segment file in bytes is equal to segment_size multiplied by block_size; by default this is 1GB.
(Description quoted from the official PostgreSQL documentation.)
How to apply a change
Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.
Inspect the current value and source with SHOW segment_size; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'segment_size';.
Tuning guidance
This is a preset, read-only parameter: it reports a value fixed when PostgreSQL was built or the cluster was initialized, and cannot be tuned at runtime. Read it to verify the server’s build or cluster configuration (for example when matching a replica or debugging a compatibility issue); there is no setting to adjust.