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From: Richard Guo <[email protected]>
To: Tom Lane <[email protected]>
Cc: David Rowley <[email protected]>
Cc: nikhil raj <[email protected]>
Cc: [email protected]
Subject: Re: Significant Execution Time Difference Between PG13.14 and PG16.4 for Query on information_schema Tables.
Date: Wed, 28 Aug 2024 11:30:45 +0800
Message-ID: <CAMbWs4_rgwHYAGr=st8XFtdbcKHCf8ti7RpHxJfzv6iZ3AgxJA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
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On Wed, Aug 28, 2024 at 5:52 AM Tom Lane <[email protected]> wrote:
> I realized that actually we do have the mechanism for making that
> work: we could apply add_nulling_relids to the expression, if it
> meets those same conditions.

I think this should work, as long as we apply add_nulling_relids only
to Vars/PHVs that belong to the subquery in this case, because only
those Vars/PHVs would be nulled by the outer joins contained in the
nullingrels.

> If we go forward with this, I'm thinking about
> changing add_nulling_relids' API contract to say "if target_relid
> is NULL then all level-zero Vars/PHVs are modified", so that we
> don't need that relid set in non-LATERAL cases.

+1.  In LATERAL case, we can always find the subquery's relids in
rcon->relids.  In non-lateral case, any level-zero Vars/PHVs must
belong to the subquery - so if we change add_nulling_relids' API to be
so, we do not need to have rcon->relids set.

Thanks
Richard






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  Cc: [email protected], [email protected], [email protected], [email protected], [email protected]
  Subject: Re: Significant Execution Time Difference Between PG13.14 and PG16.4 for Query on information_schema Tables.
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