Re: SSI implementation question

"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