Author: Peter Whyte

  • PARALLEL_REDO_LOG_CACHE Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability PARALLEL_REDO_LOG_CACHE is recorded infrequently on an Availability Group replica after the main redo thread has hit a bottleneck, that is, following episodes of PARALLEL_REDO_FLOW_CONTROL. It relates to the log cache the redo pipeline reads from,…

    Written by

    Peter Whyte

  • PARALLEL_REDO_FLOW_CONTROL Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: HADR_SYNC_COMMIT Wait TypeRelated pillar: High Availability PARALLEL_REDO_FLOW_CONTROL is recorded on an Availability Group secondary when the main redo thread has dispatched as much log as it is allowed to the parallel redo worker threads and must wait for one of them…

    Written by

    Peter Whyte

  • DBA Scripts: Get Log Reuse Waits

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    🔧Part of the DBA-Tools Project, copy/paste SQL Server scripts and health checks.In: Storage & Capacity The One Question That Actually Matters A transaction log that won’t truncate and keeps growing, or a log backup job that suddenly can’t keep up, always comes back to the same underlying question: what is this database’s log actually waiting…

    Written by

    Peter Whyte

  • PARALLEL_BACKUP_QUEUE Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: BACKUPIO and BACKUPBUFFER Wait TypesRelated pillar: Backup & Recovery PARALLEL_BACKUP_QUEUE is recorded when a thread in a parallel restore operation waits for access to a shared output result set. The commands that read backup metadata, RESTORE HEADERONLY, RESTORE FILELISTONLY, RESTORE LABELONLY,…

    Written by

    Peter Whyte

  • PAGEIOLATCH_NL Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: PAGEIOLATCH_SH Wait TypeRelated pillar: Storage & Capacity PAGEIOLATCH_NL is the Null (NL) mode member of the I/O page latch family, a placeholder so every latch mode has a PAGEIOLATCH_* counterpart. Null mode acquires nothing, and this wait type goes unused in…

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    Peter Whyte

  • PAGEIOLATCH_KP Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: PAGEIOLATCH_SH Wait TypeRelated pillar: Storage & Capacity PAGEIOLATCH_KP is a wait for a Keep (KP) mode latch on a buffer page that is currently part of an I/O request. Keep mode pins the page against destruction while the I/O is in…

    Written by

    Peter Whyte

  • PAGEIOLATCH_DT Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: PAGEIOLATCH_SH Wait TypeRelated pillar: Storage & Capacity PAGEIOLATCH_DT is a wait for a Destroy (DT) mode latch on a buffer page that is currently part of an I/O request. Destroy mode is used when a buffer is being removed, and this…

    Written by

    Peter Whyte

  • ONDEMAND_TASK_QUEUE Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: SOS_SCHEDULER_YIELD Wait TypeRelated pillar: Performance & Troubleshooting ONDEMAND_TASK_QUEUE is recorded by a background task while it waits for high-priority system task requests to arrive, DTC commit and abort processing being the documented example. The engine keeps this lane clear for work…

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    Peter Whyte

  • OLEDB Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: ASYNC_NETWORK_IORelated pillar: Performance & Troubleshooting OLEDB indicates SQL Server is waiting for an OLE DB provider call to return. This usually means linked server access and distributed queries, but the same interface is used internally, so the wait has a famous…

    Written by

    Peter Whyte

  • MSQL_XP Wait Type in SQL Server

    ⏳Part of the SQL Server Wait Types Library, every wait type explained.Related deep dive: ASYNC_NETWORK_IO Wait TypeRelated pillar: Performance & Troubleshooting MSQL_XP is recorded while a task waits for an extended stored procedure (XP) to finish. Extended stored procedures are external code, DLLs loaded into the SQL Server process, called through the old XP interface:…

    Written by

    Peter Whyte
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