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From: David Rowley <dgrowleyml@gmail.com>
Date: Fri, 1 Apr 2022 17:08:27 +1300
Message-ID: <CAApHDvrpWWtSRZXFO31H1KcC9csKuE31v2f7k6rVS9Yp5ibc7Q@mail.gmail.com>
Subject: Re: generic plans and "initial" pruning
To: Amit Langote <amitlangote09@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, 
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Fri, 1 Apr 2022 at 16:09, Amit Langote <amitlangote09@gmail.com> wrote:
> definition of PlannedStmt says this:
>
> /* ----------------
>  *      PlannedStmt node
>  *
>  * The output of the planner
>
> With the ideas that you've outlined below, perhaps we can frame most
> of the things that the patch wants to do as the planner and the
> plancache changes.  If we twist the above definition a bit to say what
> the plancache does in this regard is part of planning, maybe it makes
> sense to add the initial pruning related fields (nodes, outputs) into
> PlannedStmt.

How about the PartitionPruneInfos go into PlannedStmt as a List
indexed in the way I mentioned and the cache of the results of pruning
in EState?

I think that leaves you adding  List *partpruneinfos,  Bitmapset
*minimumlockrtis to PlannedStmt and the thing you have to cache the
pruning results into EState.   I'm not very clear on where you should
stash the results of run-time pruning in the meantime before you can
put them in EState.  You might need to invent some intermediate struct
that gets passed around that you can scribble down some details you're
going to need during execution.

> One question is whether the planner should always pay the overhead of
> initializing this bitmapset?  I mean it's only worthwhile if
> AcquireExecutorLocks() is going to be involved, that is, the plan will
> be cached and reused.

Maybe the Bitmapset for the minimal locks needs to be built with
bms_add_range(NULL, 0, list_length(rtable));  then do
bms_del_members() on the relevant RTIs you find in the listed
PartitionPruneInfos.  That way it's very simple and cheap to do when
there are no PartitionPruneInfos.

> > 4. It's a bit disappointing to see RelOptInfo.partitioned_rels getting
> > revived here.  Why don't you just add a partitioned_relids to
> > PartitionPruneInfo and just have make_partitionedrel_pruneinfo build
> > you a Relids of them. PartitionedRelPruneInfo already has an rtindex
> > field, so you just need to bms_add_member whatever that rtindex is.
>
> Hmm, not all Append/MergeAppend nodes in the plan tree may have
> make_partition_pruneinfo() called on them though.

For Append/MergeAppends without run-time pruning you'll want to add
the RTIs to the minimal locking set of RTIs to go into PlannedStmt.
The only things you want to leave out of that are RTIs for the RTEs
that you might run-time prune away during AcquireExecutorLocks().

David