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Re: Process local hint bit cache

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Process local hint bit cache
Date: 2011-03-31 16:38:59
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Wed, Mar 30, 2011 at 6:30 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Wed, Mar 30, 2011 at 2:35 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>> btw I haven't forgotten your idea to move TransactionIdInProgress
>> Down. I think this is a good idea, and will experiment with it pre and
>> post cache.
> aside:
> Moving TransactionIdInProgress below TransactionIdDidCommit can help
> in once sense: TransactionIdDidCommit grabs the XidStatus but discards
> the knowledge if the transaction is known aborted.   If it is in fact
> aborted you can immediately set the hint bits and punt. This should
> save an awful lot of calls to TransactionIdInProgress when scanning
> unhinted dead tuples.

Yeah, it might make sense to have a function that returns
commit/abort/unsure, where unsure can only happen if the transaction
ID follows RecentXmin.  You might also want to rearrange things so
that that function starts by checking the passed-in XID against
cachedFetchXid so we don't lose the benefit of that one-element cache.

Robert Haas
The Enterprise PostgreSQL Company

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