![[assets/wl_io_buffileread.png|256]] - **Description**: Occurs when PostgreSQL needs to read temporary files from disk. This typically happens when in-memory buffers for operations like sorts and hashes (controlled by `work_mem`) are exhausted, and data that was "spilled to disk" needs to be re-read. - **Operations**: - [[Operations/Hash]] - [[Operations/Materialize]] - [[Operations/HashJoin]] - [[Operations/TableFuncScan]] - [[Operations/CTEScan]] - [[Operations/MergeJoin]] - [[Operations/WindowAgg]] - [[Operations/RecursiveUnion]] - [[Operations/Aggregate]] - [[Operations/SetOp]] - [[Operations/Sort]] - **Resources**: [[Resources/disk IO]], [[Resources/CPU|CPU]]