More on daily backups..

I wrote yesterday about some oddities I was experiencing. I haven't
had a chance to get all the details together to send you but one other
strange thing is happening and it may be my lack of understanding of
how incremental backups work.

My daily backup file is about 70 megabytes, which seems to me to be
way too big. (Full backup is about 4 gig). In exploring the daily
file, I found a few things that I could deal with to improve that
situation. One was some really huge log files that needed to be set on
a rotation, so I took care of that. The other, however, is my MySQL
databases that get backed up.. I use mysqlhotcopy to make a snapshot
of the database files, then hdup backs it up.

Two odd things are happening. The huge log files are still being
backed up (e.g. they were in the 12-31 daily backup) even though their
last update date was 12-29. I would have expected them to get backed
up once more after I switched to a rotating log cycle but then never
again in an incremental. Why would these files keep getting archived?
For that matter - why would ANY file with a date stamp more than 24
hours before the previous daily backup get archived in the daily?

Also - every single file from the mysql snapshot is getting archived.
In many cases, these tables are relatively static and some have not
been updated in months. The snapshot generated by mysqlhotcopy
maintains the date stamp of the actual table, so the daily archive
reflects lots of files with very old date stamps.

How does the incremental archive determine what is changed? Why would
files with very old date stamps ever get archived?

Thanks!

-- Jamie