Re: pg_dump issues

On 10/03/2011 12:47 AM, Tom Lane wrote:
> Andrew Dunstan<andrew(at)dunslane(dot)net> writes:
>> While investigating a client problem I just observed that pg_dump takes
>> a surprisingly large amount of time to dump a schema with a large number
>> of views. The client's hardware is quite spiffy, and yet pg_dump is
>> taking many minutes to dump a schema with some 35,000 views. Here's a
>> simple test case:
>> create schema views;
>> do 'begin for i in 1 .. 10000 loop execute $$create view views.v_$$
>> || i ||$$ as select current_date as d, current_timestamp as ts,
>> $_$a$_$::text || n as t, n from generate_series(1,5) as n$$; end
>> loop; end;';
>> On my modest hardware this database took 4m18.864s for pg_dump to run.
> It takes about that on my machine too ... with --enable-cassert.
> oprofile said that 90% of the runtime was going into AllocSetCheck,
> so I rebuilt without cassert, and the runtime dropped to 16 seconds.
> What were you testing?

Yeah, you're right, that must have been it. That's a big hit, I didn't
realise cassert was so heavy. (Note to self: test with production build
settings). I don't seem to be batting 1000 ...

I still need to get to the bottom of why the client's machine is taking
so long.

I do notice that we seem to be doing a lot of repetitive tasks, e.g.
calling pg_format_type() over and over for the same arguments. Would we
be better off cacheing that?

cheers

andrew