> [!NOTE] ![[assets/wl_activity_walsenderwaitwal.png|256]] > > | | | > | :--- | :--- | > | **Wait Category** | Activity | > | **Mechanism** | `WalSenderWaitForWAL` | > | **Operations** | [[Operations/Distributed/Redistribute]] | > | **Resources** | [[Resources/disk IO]], [[Resources/CPU|CPU]] | > > **Primary-Side Durability Lag**. To ensure data integrity, a WAL Sender cannot stream records that have not yet been durably persisted to the primary's own `pg_wal` directory.