Subject Re: internal Firebird consistency check (decompression overran buffer (179), file: sqz.cpp line: 239)
I had the same thing again on a completely unrelated database that doesn't do the nightlySQL I know it isn't that. 

Following on from the question from Alexey which made me think about multi-file databases which we aren't using I've just disabled our regular NBackups that we were running 

#00 02 01 * * root /usr/local/sbin/nbackup-db 0  >/tmp/nbackup.log 2>&1
#00 03 01 * 6 root /usr/local/sbin/nbackup-db 1 >>/tmp/nbackup.log 2>&1
#00 04  * * * root /usr/local/sbin/nbackup-db 2 >>/tmp/nbackup.log 2>&1

Saturday's problem seemed to happen at 02:21, and last night if was around 04:04 ... so I've jumped to some conclusions.  That seems like too much of a coincidence given that Saturday was day "01" of the month.

Once again, because we had just done the backup in the middle of the night I was able to recover all the data from the backup so I'm still not in panic mode. Just a bit stressed!