Re: [PATCH] Incremental sort (was: PoC: Partial sort) - Mailing list pgsql-hackers

From James Coleman
Subject Re: [PATCH] Incremental sort (was: PoC: Partial sort)
Date
Msg-id CAAaqYe8HFkcM1rM92V-9mv6KbOsxwkqaSUu_xojy=wE2jaHTBQ@mail.gmail.com
Whole thread Raw
In response to Re: [PATCH] Incremental sort (was: PoC: Partial sort)  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
List pgsql-hackers
On Tue, Apr 7, 2020 at 7:58 PM Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>
> On Tue, Apr 07, 2020 at 07:50:26PM -0400, James Coleman wrote:
> >On Tue, Apr 7, 2020 at 7:02 PM Tomas Vondra
> ><tomas.vondra@2ndquadrant.com> wrote:
> >>
> >> On Mon, Apr 06, 2020 at 11:25:21PM -0500, Justin Pryzby wrote:
> >> >On Mon, Apr 06, 2020 at 09:57:22PM +0200, Tomas Vondra wrote:
> >> >> I've pushed the fist part of this patch series - I've reorganized it a
> >> >
> >> >I scanned through this again post-commit.  Find attached some suggestions.
> >> >
> >>
> >> Thanks. The typo fixes seem clear, except for this bit:
> >>
> >>    * If we've set up either of the sort states yet, we need to reset them.
> >>    * We could end them and null out the pointers, but there's no reason to
> >>    * repay the setup cost, and because ???? guard setting up pivot comparator
> >>    * state similarly, doing so might actually cause a leak.
> >>
> >> I can't figure out what ???? should be. James, do you recall what this
> >> should be?
> >
> >Yep, it's ExecIncrementalSort. If you look for the block guarded by
> >`if (fullsort_state == NULL)` you'll see the call to
> >preparePresortedCols(), which sets up the pivot comparator state
> >referenced by this comment.
> >
>
> OK, so it should be "... and because ExecIncrementalSort guard ..."?

Yes, "because ExecIncrementalSort guards presorted column functions by
checking to see if the full sort state has been initialized yet,
setting the sort states to null here might cause..." (that's more
specific IMO than my original "pivot comparator state...doing so").

James



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