SQL Server distribution database log file grows uncontrollably after full database backup We have a merge replication environment that is pushing to 8 subscribers. This is working fine. Our distribution database is setup in Simple recovery mode. We have a maintenance plan that will backup all database every day at 00:30. Once this process completes, the distribution log file grows over the next 30 minutes and absorbs all the remaining space on the hard drive (about 90GB)

What then happens is that the distribution database shows as "Recovery Pending" and we cannot do anything till we restart the machine. After this I can shrink the log file down to 2MB.

I have no idea why this is happening. The log file is running at about 10MB during the day. The database size is sitting at 15GB.
It sounds like you have a high volume of transactions happening with your replication. If so, that "clean up: distribution" job should probably be running far more often. It sounds to me like it's happening once a day. On my high transaction replication server I have it running every 15 minutes to keep just the latest 36 hours. That way it paces itself and doesn't bog down.

Here's an article that might help - http://www.sqlservergeeks.com/blogs/singhsatnam84/sql-server-bi/563/sql-server-controlling-growth-of-a-distribution-database