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If I'm failing over my server due to a OS patch, are in-process transactions allowed to finish before stopping the SQL service?

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up vote 1 down vote accepted

No. Transaction state is "incomplete" or "uncommitted"

When the SQL Server Instance starts, it goes through recovery to redo completed/undo uncommitted transactions

All work is deferred to start up because the reasons for SQL Server shutdown can be many and varied. This isn't known at start up: so redo/undo always happens

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So all transactions in the buffer pool since the last checkpoint are lost, correct? I would have thought that sql would run a checkpoint before shutting off. – Sam Jul 21 '11 at 21:12
A Checkpoint isn't a commit: it flushes dirty pages to disk – gbn Jul 22 '11 at 6:26

Either using cluster administrator to manually failover or having a cluster failure it's all the same. As the databases are brought online on the new node they will go through a recovery where completed transactions are rolled forward and incomplete transactions are rolled back.

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