Re: SSI implementation question

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Dan Ports <drkp@csail.mit.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