SQL Server sys.databases log_reuse_wait question

Question

I was investigating the rapid growth of a SQL Server 2005 transaction log when I found that transaction logs will only truncate correctly - if the sys.databases "log_reuse_wait" column is set to 0 - meaning that nothing is keeping the transaction log from reusing existing space.

One day when I was intending to backup/truncate a log file, I found that this column had a 4, or ACTIVE_TRANSACTION going on in the tempdb. I then checked for any open transactions using DBCC OPENTRAN('tempdb'), and the open_tran column from sysprocesses. The result was that I could find no active transactions anywhere in the system.

Are the settings in the log_reuse_wait column accurate? Are there transactions going on that are not detectable using the methods I described above? Am I just missing something obvious?

Answer 1

I still don't know why I was seeing the ACTIVE_TRANSACTION in the sys.databases log_reuse_wait_desc column - when there were no transactions running, but my subsequent experience indicates that the log_reuse_wait column for the tempdb changes for reasons that are not very clear, and for my purposes, not very relevant. Also, I found that running DBCC OPENTRAN, or the "select open_tran from sysprocess" code, is a lot less informative than using the below statements when looking for transaction information:

select * from sys.dm_tran_active_transactions

select * from sys.dm_tran_session_transactions 

select * from sys.dm_tran_locks