Specifies the amount of shared memory to use to cache the contents of pg_multixact/members (see pgdata_contents_table).
At a glance
| Property | Value |
|---|---|
| Parameter | multixact_member_buffers |
| Category | Resource Consumption |
| Default | 32 |
| Value type | integer |
| Change scope | Server restart required (postgresql.conf) |
| Available in | PostgreSQL 17, 18, 19 (added in 17) |
What it does
Specifies the amount of shared memory to use to cache the contents of pg_multixact/members (see pgdata_contents_table). If this value is specified without units, it is taken as blocks, that is BLCKSZ bytes, typically 8kB. The default value is 32. This parameter can only be set at server start.
(Description quoted from the official PostgreSQL documentation.)
How to apply a change
Set it in postgresql.conf (or with ALTER SYSTEM) and restart the server — this parameter cannot change without a restart.
Inspect the current value and source with SHOW multixact_member_buffers; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'multixact_member_buffers';.
Tuning guidance
This parameter is rarely a performance lever. Leave it at the default unless you have a specific, documented reason to change it, change it on one session or one role/database first, and confirm the effect with pg_settings and your own measurements before rolling it out cluster-wide.