LOG_BACKUP wait type for Transaction log file of a simple recovery model database

Question

A few minutes ago I ran into a strange situation with my prod database. I have db X with simple recovery model. SCOM gave me an alert that the log disk is running out of space. I then checked the disk and saw that db X's log file is 11 Gb even though the data file is 300 Mb and the recovery model is simple.

Then I checked DBCC OPENTRAN but there were no open transactions, neither on the database nor on the server.

Then I tried to shrink the log file, but it said that there was no empty space. I checked the log_reuse_wait_type column and it was LOG_BACKUP. I know that, by definition, it should be impossible to see that wait type for a database using the SIMPLE recovery model, but there it was. I double checked all the steps that I mentioned above and nothing changed. Then I changed the recovery model of db X to FULL and set it back to SIMPLE. After that log_reuse_wait_type reported as NOTHING.

In the end I solved the problem but still wonder why it happened. Has anyone encountered a similar problem?

Answer 1

Are you running SQL Server 2012? Is your model database in SIMPLE recovery model? Are you a bit behind with your patching?

This appears to have been the issue for a previous ask of this question, at SQL Server 2012 Simple Recovery Model with LOG_BACKUP log_reuse_wait_desc

Fixed in KB2830400 which forms part of SQL Server 2012 CU7 / SQL Server 2012 SP1 CU 4