> [!NOTE] ![[assets/wl_io_walsummaryread.png|256]] > > | | | > | :--- | :--- | > | **Wait Category** | IO | > | **Mechanism** | `WALSummarizer` | > | **Operations** | [[Operations/Distributed/Redistribute]] | > | **Resources** | [[Resources/disk IO]], [[Resources/CPU|CPU]] | > > **Incremental Backup Metadata Retrieval stall**. Introduced in Postgres 17, WAL summary files provide a condensed map of which blocks were modified in a range of WAL segments.