IO:SLRURead
SLRURead is a PostgreSQL wait event that occurs when a backend process is waiting to read a page from a SLRU (Simple LRU) buffer structure on disk.
SLRUs are used internally by PostgreSQL to manage certain types of fixed-size, disk-backed data that benefit from a simple least-recently-used caching strategy.
Common subsystems that use SLRUs include:
- Commit Log (CLOG) tracks transaction commit status,
- Subtransaction Log (SUBTRANS) records parent-child transaction relationships,
- MultiXact members and offsets used for shared row locks,
- Serialized predicate lock (predicate locks for SERIALIZABLE isolation).
When a needed SLRU page isn’t in memory, PostgreSQL reads it from disk, triggering the SLRURead wait event.