From: Andy Fan <zhihuifan1213@163.com>
To: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Why does exec_simple_query requires 2 snapshots
Date: Tue, 18 Feb 2025 11:48:30 +0000
Message-ID: <87o6yzbhip.fsf@163.com>
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Hi,

When I run "SELECT * FROM pg_class LIMIT 1";  then postgresql
run GetSnapshotData twice, one is

/*
 * Set up a snapshot if parse analysis/planning will need one.
 */
if (analyze_requires_snapshot(parsetree))
{
	PushActiveSnapshot(GetTransactionSnapshot());
	snapshot_set = true;
}


the other one is in PortalStart.

My question is why can't we share the same snapshot for the 2 cases?
parser & planner requires Catalog Snapshot which should be the 
latest one, but in the above case, looks the executor can reuse it as
well. Is there anything I missed?

Thanks

-- 
Best Regards
Andy Fan