Re: Further pg_upgrade analysis for many tables

On Fri, Nov 9, 2012 at 10:50 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Thu, Nov 8, 2012 at 9:50 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
>>> Are sure the server you are dumping out of is head?
>>
>> I experimented a bit with dumping/restoring 16000 tables matching
>> Bruce's test case (ie, one serial column apiece). The pg_dump profile
>> seems fairly flat, without any easy optimization targets. But
>> restoring the dump script shows a rather interesting backend profile:
>>
>> samples % image name symbol name
>> 30861 39.6289 postgres AtEOXact_RelationCache
>> 9911 12.7268 postgres hash_seq_search
> ...
>>
>> There are at least three ways we could whack that mole:
>>
>> * Run the psql script in --single-transaction mode, as I was mumbling
>> about the other day. If we were doing AtEOXact_RelationCache only once,
>> rather than once per CREATE TABLE statement, it wouldn't be a problem.
>> Easy but has only a narrow scope of applicability.
>
> That is effective when loading into 9.3 (assuming you make
> max_locks_per_transaction large enough). But when loading into <9.3,
> using --single-transaction will evoke the quadratic behavior in the
> resource owner/lock table and make things worse rather than better.

Using --single-transaction gets around the AtEOXact_RelationCache
quadratic, but it activates another quadratic behavior, this one in
"get_tabstat_entry". That is a good trade-off because that one has a
lower constant, but it is still going to bite.

Cheers,

Jeff