Re: pg_dump custom format without timestamp?

Dear Tom,

thanks for your answer,

> Fabien COELHO <coelho@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 $previous
&¤t=$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.