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From: Amit Langote <amitlangote09@gmail.com>
Date: Fri, 1 Apr 2022 16:01:18 +0900
Message-ID: <CA+HiwqGf5PrQ8RX2So7g0y75xN_jVs6W0pvfUKv6zS+KYMGsig@mail.gmail.com>
Subject: Re: generic plans and "initial" pruning
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>, Robert Haas <robertmhaas@gmail.com>, 
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Fri, Apr 1, 2022 at 12:45 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Amit Langote <amitlangote09@gmail.com> writes:
> > On Fri, Apr 1, 2022 at 10:32 AM David Rowley <dgrowleyml@gmail.com> wrote:
> >> 1. You've changed the signature of various functions by adding
> >> ExecLockRelsInfo *execlockrelsinfo.  I'm wondering why you didn't just
> >> put the ExecLockRelsInfo as a new field in PlannedStmt?
>
> > I'm worried about that churn myself and did consider this idea, though
> > I couldn't shake the feeling that it's maybe wrong to put something in
> > PlannedStmt that the planner itself doesn't produce.
>
> PlannedStmt is part of the plan tree, which MUST be read-only to
> the executor.  This is not negotiable.  However, there's other
> places that this data could be put, such as QueryDesc.
> Or for that matter, couldn't the data structure be created by
> the planner?  (It looks like David is proposing exactly that
> further down.)

The data structure in question is for storing the results of
performing initial partition pruning on a generic plan, which the
proposes to do in plancache.c -- inside the body of
AcquireExecutorLocks()'s loop over PlannedStmts -- so, it's hard to
see it as a product of the planner. :-(

-- 
Amit Langote
EDB: http://www.enterprisedb.com