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Re: [Bizgres-general] WAL bypass for INSERT, UPDATE and

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, simon(at)2ndquadrant(dot)com, kleptog(at)svana(dot)org, gsstark(at)mit(dot)edu, pg(at)rbt(dot)ca, zhouqq(at)cs(dot)toronto(dot)edu, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [Bizgres-general] WAL bypass for INSERT, UPDATE and
Date: 2006-01-03 16:48:01
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
"Jim C. Nasby" <jnasby(at)pervasive(dot)com> writes:
> On Tue, Jan 03, 2006 at 11:26:51AM -0500, Tom Lane wrote:
>> Such an ALTER would certainly require exclusive lock on the table,
>> so I'm not sure that I see much use-case for doing it like that.
>> You'd want to do the ALTER and commit so as not to lock other people
>> out of the table entirely while doing the bulk data-pushing.

> Maybe this just isn't clear, but would EXCLUSIVE block writes from all
> other sessions then?

I don't think it should (which implies that EXCLUSIVE is a bad name).
My point is that ALTER RELIABILITY would have to gain exclusive lock
for long enough to change the table's reliability marking --- you have
to synchronize such a change with other transactions' activity on the
table, and table-level locks are the only mechanism we have for that.
It's not different from a schema change such as adding a column.

			regards, tom lane

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