![[wl_io_datafileread.png|256]] - **Description**: Occurs when a backend process needs to read a required page from storage because it is not currently available in shared memory. High rates of this event suggest that the shared buffer pool is too small for the active working set. - **Operations**: - [[IndexScan]] - [[TidScan]] - [[SeqScan]] - [[BitmapIndexScan]] - [[MergeJoin]] - [[BitmapHeapScan]] - [[NestedLoop]] - [[IndexOnlyScan]] - [[SampleScan]] - [[CustomScanForeignScan]] - **Resources**: [[Disk IO]], [[CPU]]