What do the bufwait, writelog and buffer latch errors in SQL Server mean?

A. The following errors can occur :-

writelog: timeout, dbid <x>, ...........

bufwait: timeout, BUF_IO .....

Time out occurred while waiting for buffer latch type 2, bp 0x11cfc580, page (0:0), stat 0x405, object ID 7:1:0, waittime 500. Continuing to wait.

As long as SQL Server carries on, and no other errors are being reported, then there is usually nothing to worry about. They are merely showing that the disk subsystem is unable to keep up with the level of i/o that SQL Server is asking it to do. SQL just waits and retries these requests. (The message *may* indicate that the disk subsystem is experiencing problems - check the NT event log for scsi errors and any hardware monitoring tools you have)

To up the amount of time that SQL waits before issuing this message and retrying amend the "resource timeout" parameter via sp_configure. (Only applies to SQL 6.5)

You MAY need to decrease your max async io (any version) or max lazywrite io (SQL 6.5 only) if these errors are continuous. Or invest in a faster disk subsystem. Or spread your devices across more of your existing spindles.

See article Q167711 in the Microsoft Knowledgebase/Technet for more info.

If SQL does not automatically carry on then either a memory corruption has occured with the internal SQL data structures or a hardware error is preventing SQL from getting a response.


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