From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Heikki Linnakangas <hlinnaka@iki.fi>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        pgsql-hackers@postgresql.org
Subject: Re: WIP: Faster Expression Processing v4
In-reply-to: <20170314224706.nxvtapenky6eom3z@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Tue, 14 Mar 2017 15:47:06 -0700"
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Date: Wed, 15 Mar 2017 15:33:28 -0400
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Andres Freund <andres@anarazel.de> writes:
> [ latest patches ]

I looked through 0002-Make-get_last_attnums-more-generic.patch.
Although it seems relatively unobjectionable on its own, I'm not
convinced that it's really useful to try to split it out like this.
I see that 0004 removes the only call of ExecGetLastAttnums (the
one in ExecBuildProjectionInfo) and then adds a single call in
ExecInitExprSlots which is in execExpr.c.  To me, the only reason
ExecGetLastAttnums nee get_last_attnums is in execUtils.c in the first
place is that it is a private subroutine of ExecBuildProjectionInfo.
After these changes, it might as well be a private subroutine of
ExecInitExprSlots.  I'm suspicious of turning it into a globally
accessible function as you've done here, because I doubt that it is of
global use --- in particular, the fact that it doesn't deal specially
with INDEX_VAR Vars seems rather specific to this one use-case.

So for my money, you should drop 0002 altogether and just have 0004
remove get_last_attnums() from execUtils.c and stick it into
execExpr.c.  I suppose you still need the LastAttnumInfo API change
so as to decouple it from ProjectionInfo, but that's minor.

			regards, tom lane


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