"Timeout occurred while waiting for latch" error when running DBCC CHECKDB statement on a database

This article introduces a problem where you receive an error message when you try to run the DBCC CHECKDB statement on a database that contains a large table in SQL Server.

Original product version:   SQL Server
Original KB number:   919155

Symptoms

Consider the following scenario:

• You have a database that contains one or more very large tables.
• The tables are typically several hundred gigabytes (GB) in size.
• You run the DBCC CHECKDB statement on the database in SQL Server.

In this scenario, an error message that resembles the following is written to the SQL Server error log:

<DateTime> spid65 Timeout occurred while waiting for latch: class 'DBCC_MULTIOBJECT_SCANNER', id 000000002201DED0, type 4, Task 0x000000000C80BEB8 : 6, waittime 300, flags 0xa, owning task 0x0000000005A0AC58. Continuing to wait.

However, the DBCC CHECKDB statement will complete successfully. You can safely ignore the error message.

Cause

This issue occurs because a time-out occurs when SQL Server traverses the Index Allocation Map (IAM) chains. The latch that is mentioned in the error message is used to prevent other threads from accessing a list. This list is being built by a thread that traverses the IAM chains for all indexes that are associated with a given table. If the table is large enough that traversing these IAM chains takes more than 5 minutes, you may experience the latch time-out. Additionally, this issue is typically worse when disk I/O is slow.

Status

This behavior is by design.