NOLOCK Bug

Brent Ozar reports on a NOLOCK bug in SQL Server 2014 SP1 CU6:

  • While one transaction is holding an exclusive lock on an object (Ex. ongoing table update), another transaction is executing parallelized SELECT (…) FROM SourceTable, using the NOLOCK hint, under the default SQL Server lock-based isolation level or higher. In this scenario, the SELECT query trying to access SourceTable will be blocked.

  • Executing a parallelized SELECT (…) INTO Table FROM SourceTable statement, specifically using the NOLOCK hint, under the default SQL Server lock-based isolation level or higher. In this scenario, other queries trying to access SourceTable will be blocked.

The current recommendation is not to install CU6 until the issue is fixed.

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