[Duplicity-talk] incremental database backup

[birched]

Hi,

I'm having some trouble with duplicity and backing up a database. 
Specifically, duplicity seems to be backing up the full (.tgz compressed)
database every time.

I would like very much to get the incremental backup scheme working, if
possible, to minimize the amount of information I need to transfer (the
database is about 1.3 GB).

My setup:
*note that the name of the source backup directory changes depending on
the day (we keep 7 day-by-day backups, and I am backing up from the most
recent of them); I've 'allowed source mismatch' to account for that, but
perhaps I misunderstood how that works?

duplicity 0.6.06
export PASSPHRASE="xyz"
DBTARGET="scp://address@hidden/xyz"
DUPLICITY="/usr/local/bin/duplicity"
FILEOPTIONS='--exclude-globbing-filelist /x/y/z/file.txt'
DBOPTIONS='--allow-source-mismatch'
DBBACKUPDIR="/backup/DBbackups/daily/$(date +"%u")"


$DUPLICITY $BACKUPTYPE --scp-command "scp -l 100" --encrypt-key="AD438929"
$DBOPTIONS $DBBACKUPDIR $DBTARGET


Here's a record of a recent 'incremental' backup (files are the same, but
they may have been located in /x/y/z/1/ on one day and /x/y/z/2/ on the
second):
--------------[ Backup Statistics ]--------------
StartTime 1267738614.76 (Thu Mar  4 16:36:54 2010)
EndTime 1267743292.64 (Thu Mar  4 17:54:52 2010)
ElapsedTime 4677.88 (1 hour 17 minutes 57.88 seconds)
SourceFiles 12
SourceFileSize 1312756951 (1.22 GB)
NewFiles 1
NewFileSize 4096 (4.00 KB)
DeletedFiles 0
ChangedFiles 11
ChangedFileSize 1312752855 (1.22 GB)
ChangedDeltaSize 0 (0 bytes)
DeltaEntries 12
RawDeltaSize 1306027743 (1.22 GB)
TotalDestinationSizeChange 1314667526 (1.22 GB)
Errors 0
-------------------------------------------------


I'm not sure where I've gone wrong, but I think my questions are:
1. does using a tgz archive mess up the incremental backup scheme?  is it
possible that this will only work if I leave the databases in a
(substantially larger) SQL format?
2. does allow-source-mismatch make up for the directory changes, or do I
need to repattern our nightly backups so that duplicity can always take
files from a directory of the same name?

And finally, one more (though perhaps I should put this in a separate
e-mail?)
3. verify takes a very long time -- long enough that I eventually decided
against using it as part of my regular backup scheme... is this normal?

Thanks,
Mark