Re: Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>
Cc: "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit
Date: 2008-03-10 15:20:40
Message-ID: 24304.1205162440@sss.pgh.pa.us
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"Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:
> The oprofile output is pretty damning:

> samples % symbol name
> 42148 99.7468 TransactionIdIsCurrentTransactionId

Oh, I have no doubt that that could eat a lot of cycles inside the
originating transaction ;-). I just misread Craig's complaint as
being about the cost of the first table scan *after* that transaction.

Getting rid of the linked-list representation would be a win in a couple
of ways --- we'd not need the bogus "list of XIDs" support in pg_list.h,
and xactGetCommittedChildren would go away. OTOH AtSubCommit_childXids
would get more expensive.

regards, tom lane

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