Dear Tom,
thanks for your answer,
Fabien COELHO <coe...@cri.ensmp.fr> writes:
I was looking into using hardlinks to reduce the storage of keeping and
syncing periodic database dumps when they are identical. This works fine
with the textual format, but not for the custom format because the file
header includes a timestamp set by function WriteHead in file
"src/bin/pg_dump/pg_backup_archiver.c".
I'm not sure about this goal ...
That may be debatable. I just want "easy longterm dumps" with rotations on
small databases, and I can do that in a few line of shell using links,
something like:
# on every hour
pg_dump <some options> base > $current
# is it identical to the previous one?
cmp $current $previous && current=$previous
ln $current $(date +H%H) # H00 .. H23 / hourly, daily rotation
ln $current $(date +%a) # Mon .. Sun / daily, weekly rotation
ln $current $(date +W%D) # W01 .. W53 / weekly, yearly rotation
ln $current $(date +%b) # Jan .. Dec / monthly, yearly rotation
ln $current $(date +Y%Y) # Y2012 .. Y20XX / yearly, no rotation
mv $current $previous
In order to circumvent this issue, I would think of adding a
"--no-timestamp" option to pg_dump and put zeros everywhere in place of
the actual timestamp in such case, and possibly ignoring the said
timestamp in function ReadHead.
... and quite dislike this solution.
I agree that it is a little bit ugly. I'm not sure that it was a good idea
add a timestamp in the dump format. From a system perspective, the file is
already timestamped when created, so this somehow is redundant. Well, one
may lost the timestamps.
pg_dump has way too many bizarre options already. Perhaps you should
consider making a bit of code that knows how to compare two custom dumps
ignoring the timestamp.
I could do that, but I like a simple "cmp" in a simple shell script,
rather than a custom comparison command. The backup is really to do a "cmp
-i XX" to blindly skip part of the header.
--
Fabien.
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