Re: PGSQL 7.4.8 : idle in transaction problem

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От Tom Lane
Тема Re: PGSQL 7.4.8 : idle in transaction problem
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Msg-id 15465.1121866521@sss.pgh.pa.us
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Ответ на Re: PGSQL 7.4.8 : idle in transaction problem  (Alvaro Herrera <alvherre@alvh.no-ip.org>)
Ответы Re: PGSQL 7.4.8 : idle in transaction problem  (Brad Nicholson <bnichols@ca.afilias.info>)
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Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On Tue, Jul 19, 2005 at 10:44:35PM -0400, Tom Lane wrote:
>> If it's a matter of whether VACUUM removes rows or not, that's expected:
>> open-transaction bookkeeping is done across the whole cluster.  (This is
>> not something simple to change, since we may have to consider
>> transaction IDs in shared catalogs.)

> I wonder if this restriction could be lifted if we tracked last-vacuum-
> Xid per relation?

No, that's unrelated.  What is of concern is the open-transaction
horizon.  We could tighten things up by keeping a more complicated set
of information in the PGPROC array --- rather than advertising a single
transaction XMIN, each transaction would have to calculate and advertise
both a "global" XMIN and a "local" XMIN (the latter counting only open
transactions within your own database).  This would then allow a more
refined calculation in GetOldestXmin().

I'm inclined to think that the benefit wouldn't be worth the distributed
cost of doing this in every GetSnapshotData() call ...

            regards, tom lane

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