Re: pg_dumpall 8.1.4 large objects error

On Fri, 9 Jun 2006, Tom Lane wrote:

>> pg_dump: SQL command failed
>> pg_dump: Error message from server: ERROR:  Memory exhausted in AllocSetAlloc(96)
>
> Hm, I'm not sure why it did that.  Possibly an ANALYZE on pg_largeobject
> would change the plan for the SELECT DISTINCT and get you out of
> trouble.
>
>> Would it be better and more efficient to just pg_dumpall the globals and
>> pg_dump in custom format the vsl_cs db?
>
> Won't help AFAIK --- that query will be used for blob dumping in all
> cases.  Or actually, according to the cursor name, this is the query
> for dumping blob comments.
>
>> Server is 7.3.2, and the plan is to upgrade it.
>
> Might be worth your while to update the server to 7.3.latest in-place.
> The list of bugs fixed in 7.3.x is very long; I'm too lazy to look and
> see if any of them look related to this, but it's possible.

The in-place upgrade was going to be my next question, but that'll require
another maintenance window.  I was really hoping to get a good backup before
the next time we take it down. :-/

> Also, if you don't mind altering pg_dump, it looks to me like the query
> being used here is unnecessarily inefficient:
>
>    /* Cursor to get all BLOB comments */
>    if (AH->remoteVersion >= 70200)
>        blobQry = "DECLARE blobcmt CURSOR FOR SELECT DISTINCT loid, obj_description(loid, 'pg_largeobject') FROM
pg_largeobject";
>
> This is computing obj_description() redundantly for each pg_largeobject
> chunk.  Perhaps there is a memory leak in obj_description() in 7.3.2?
> If so it'd help to use
>
> DECLARE blobcmt CURSOR FOR
>  SELECT loid, obj_description(loid,'pg_largeobject')
>  FROM (SELECT DISTINCT loid FROM pg_largeobject) ss;

I'll alter pg_dump and recompile, then give a test.  Does pg_dumpall just call
pg_dump or do I need to change it there too?   Thanks for the help Tom.  I'll
report back with the status.

--
Jeff Frost, Owner     <jeff@frostconsultingllc.com>
Frost Consulting, LLC     http://www.frostconsultingllc.com/
Phone: 650-780-7908    FAX: 650-649-1954