Full and log backup routines

[Elias Martenson]

I'm trying to understand how to set up the backup routines in order to be completely safe.

As far as I can understand from reading the manuals, a full (not checkpointed) backup is not guaranteed to be useful in restoring the database. You always need at least one log backup taken after the full backup was finished. This is all good, so I decided to set up the backup routines so that a log backup was always made right after the full backup and this log backup will them also be backed up to tape. This should guarantee that I could always go back to the last nightly backup, in case disaste strikes and all my disks are wiped.

Now for my problem. It appears that you can't take a log backup unless you have at least one full page of data in the log. That means, that if I have an empty log, take a full backup, and then try to take a log backup, the log backup will fail.

In this particular situation, all will be well though because since no transaction happened during the full backup, this backup will be consistent.

However, since at least one page (8 kB?) of data needs to be in the log for the log backup to work, there is the potential for a situation where a very small transaction occurs during the full backup, thus rendering the full backup inconsistent, but the transaction was small enough to prevent a log backup from being taken. In this situation I will not be able to recover using my nightly backup.

Is my understanding of the situation correct? (hopefully I'm wrong) and in that case, how is this supposed to work?

Thanks in advance
Elias M�rtenson



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