Re: [PERFORM] pg_dump and thousands of schemas

On Thu, Aug 30, 2012 at 8:17 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Thu, Aug 30, 2012 at 4:51 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Bruce Momjian <bruce(at)momjian(dot)us> writes:
>>>> On Thu, May 31, 2012 at 09:20:43AM +0900, Tatsuo Ishii wrote:
>>>>> Ok, I modified the part of pg_dump where tremendous number of LOCK
>>>>> TABLE are issued. I replace them with single LOCK TABLE with multiple
>>>>> tables. With 100k tables LOCK statements took 13 minutes in total, now
>>>>> it only takes 3 seconds. Comments?
>
>>>> Was this applied?
>
>>> No, we fixed the server side instead.
>
>> But only for 9.2, right? So people running back branches are still screwed.
>
> Yeah, but they're screwed anyway, because there are a bunch of O(N^2)
> behaviors involved here, not all of which are masked by what Tatsuo-san
> suggested.

All of the other ones that I know of were associated with pg_dump
itself, and since it is recommended to run the newer version of
pg_dump against the older version of the server, no back patching
would be necessary to get the benefits of those particular fixes.

> Six months or a year from now, we might have enough confidence in that
> batch of 9.2 fixes to back-port them en masse. Don't want to do it
> today though.

What would be the recommendation for people trying to upgrade, but who
can't get their data out in a reasonable window?

Putting Tatsuo-san's change into a future pg_dump might be more
conservative than back-porting the server's Lock Table change to the
server version they are trying to get rid of.

Cheers,

Jeff