Message-ID: <44CCF8B0.5080406@joeconway.com>
Date: Sun, 30 Jul 2006 11:21:36 -0700
From: Joe Conway <mail@joeconway.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-hackers@postgresql.org
Subject: Re: [PATCHES] 8.2 features?
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Tom Lane wrote:
> So what I'm currently thinking is
> 
> 1. Implement ValuesScan.
> 2. Convert all existing uses of Result without a child node into
>    ValuesScan.
> 3. Rename Result to Filter and rip out whatever code is only used for
>    the no-child-node case.
> 
> Steps 2 and 3 are just in the nature of housekeeping and can wait till
> after the VALUES feature is in.

Sounds good to me.

> As far as avoiding overhead goes, here's what I'm thinking:
> 
> * The Values RTE node should contain a list of lists of bare
> expressions, without TargetEntry decoration (you probably do not
> need ResTarget in the raw parse tree for VALUES, either).
> 
> * The ValuesScan plan node will just reference this list-of-lists
> (avoiding making a copy).  It will need to contain a targetlist
> because all plan nodes do, but the base version of that will just
> be a trivial "Var 1", "Var 2", etc.  (The planner might replace that
> with a nontrivial targetlist in cases such as the example above.)

I'll work on that today.

> * At runtime, ValuesScan evaluates each sublist of expressions and
> stores the results into a virtual tuple slot which is returned as
> the "scan tuple" to execScan.  If the targetlist is nontrivial then
> it is evaluated with this tuple as input.  If the targetlist is
> a trivial Var list then the existing "physical tuple" optimization
> kicks in and execScan will just return the scan tuple unmodified.
> So for INSERT ... VALUES, the execScan layer will cost us nothing
> in memory space and not much in execution time.
> 
> There are still some things I don't like about the way you did
> ValuesScan but I'll work on improving that.

OK.

Thanks,

Joe