![[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**: - [[Hash]] - [[Materialize]] - [[HashJoin]] - [[TableFuncScan]] - [[CTEScan]] - [[MergeJoin]] - [[WindowAgg]] - [[RecursiveUnion]] - [[Aggregate]] - [[SetOp]] - [[Sort]] - **Resources**: [[Disk IO]], [[CPU]]