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Re: wCTE: about the name of the feature

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: wCTE: about the name of the feature
Date: 2011-02-26 05:30:25
Message-ID: 7653.1298698225@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Yay!  I'm excited about this, particularly the possible "pipelining"
> stuff, where you can do WITH (DELETE .. RETURNING ..) INSERT ...  and
> have it be like cool and fast and stuff.

> Or at least I hope you can do that.

It's gonna need some work yet.  As things stand, the tuples are indeed
pipelined through, but the CteScan nodes *also* stash them aside into
tuplestores, just in case somebody demands a rescan.  Fixing that will
require revisiting the exec flags (EXEC_FLAG_REWIND etc).  We don't
currently distinguish "it's unlikely you'll have to rescan" from
"you're guaranteed not to have to rescan", but a CteScan that's covering
a ModifyTable has to know the latter to not have to keep hold of copies
of the RETURNING tuples.

It might be a small enough change to do after alpha starts, but I don't
have time for it right now.

			regards, tom lane

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