On 14/03/2024 14:34, Robert Haas wrote:
On Thu, Mar 14, 2024 at 6:37 AM Heikki Linnakangas <hlinn...@iki.fi> wrote:
If es_snapshot was different from the active snapshot, things would get
weird, even without parallel query. The scans would use es_snapshot for
the visibility checks, but any functions you execute in quals would use
the active snapshot.
Hmm, that's an interesting point.
The case where the query is suspended and resumed - i.e. cursors are
used - probably needs more analysis. In that case, perhaps there's
more room for the snapshots to diverge.
The portal code is pretty explicit about it, the ExecutorRun() call in
PortalRunSelect() looks like this:
PushActiveSnapshot(queryDesc->snapshot);
ExecutorRun(queryDesc, direction, (uint64) count,
portal->run_once);
nprocessed = queryDesc->estate->es_processed;
PopActiveSnapshot();
I looked at all the callers of ExecutorRun(), and they all have the
active snapshot equal to queryDesc->snapshot, either because they called
CreateQueryDesc() with the active snapshot before ExecutorRun(), or they
set the active snapshot like above.
--
Heikki Linnakangas
Neon (https://neon.tech)
