Re: pg_dump custom format without timestamp?

Dear Tom,

thanks for your answer,

> Fabien COELHO <coelho(at)cri(dot)ensmp(dot)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.