"Florian G. Pflug" <[EMAIL PROTECTED]> writes:
> Sounds good, if we decide to go with the transient XID idea. So below
> for an alternative that I just came up with.

This proposal appears to require taking and releasing a brand-new lock
type every time a snapshot is made or destroyed.  That is certainly not
going to be less overhead than the transient-XID scheme.  At least in
READ COMMITTED mode, there are normally multiple snapshots taken per

(Something worth noting here is that I expect soon, probably 8.4,
we will fix things so that what a backend advertises in MyProc->xmin
is the xmin of its oldest still-live snapshot.  That means that xmin
will change intra-transaction in READ COMMITTED mode, and thus that
we would indeed need to take and release the sort of lock you are
suggesting each time.)

                        regards, tom lane

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