Controls the maximum number of I/O operations that one process can execute simultaneously.
At a glance
| Property | Value |
|---|---|
| Parameter | io_max_concurrency |
| Category | Resource Consumption |
| Default | (see documentation) |
| Value type | integer |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 18, 19 (added in 18) |
What it does
Controls the maximum number of I/O operations that one process can execute simultaneously.
The default setting of -1 selects a number based on shared_buffers and the maximum number of processes (max_connections, autovacuum_worker_slots, max_worker_processes and max_wal_senders), but not more than 64.
(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 io_max_concurrency; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'io_max_concurrency';.
Tuning guidance
Raise it on storage that benefits from many in-flight requests (NVMe, cloud block storage) so prefetch can saturate the device; too high wastes effort on a single slow disk.