From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | "Dan Ports" <drkp(at)csail(dot)mit(dot)edu>, pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: SSI implementation question |
Date: | 2011-10-19 21:52:33 |
Message-ID: | 20067.1319061153@sss.pgh.pa.us |
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"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Dan Ports <drkp(at)csail(dot)mit(dot)edu> wrote:
>> the sxact's lastCommitBeforeSnapshot needs to match the snapshot,
>> SxactGlobalXmin needs to be set to the correct value, etc. That's
>> why the call to GetSnapshotData happens from where it does
> Oh, right. I knew I was forgetting something. What if that was
> captured as part of building a snapshot? That seems like it would
> be a trivial cost compared to other snapshot-building activity, and
> might give us a way to get this out from under the
> SerializableXactHashLock locking.
But aren't the values you need to fetch protected by
SerializableXactHashLock? Having to take an additional LWLock is
*not* a "trivial cost".
regards, tom lane
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