From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: heapgettup() with NoMovementScanDirection unused in core? |
Date: | 2023-01-27 21:40:01 |
Message-ID: | CAAKRu_ZOScXUA+pSX3QEn2QP++V8Ho_oGwR_tRoP1OMn6MMGsg@mail.gmail.com |
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Lists: | pgsql-hackers |
Hi,
I have written the patch to remove the unreachable code in
heapgettup_pagemode]().
On Wed, Jan 25, 2023 at 10:02 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> I wonder if we couldn't also get rid of this confusingly-inconsistent
> alternative usage in the planner:
>
> * 'indexscandir' is one of:
> * ForwardScanDirection: forward scan of an ordered index
> * BackwardScanDirection: backward scan of an ordered index
> * NoMovementScanDirection: scan of an unordered index, or don't care
> * (The executor doesn't care whether it gets ForwardScanDirection or
> * NoMovementScanDirection for an indexscan, but the planner wants to
> * distinguish ordered from unordered indexes for building pathkeys.)
>
> While that comment's claim is plausible, I think it's been wrong for
> years. AFAICS indxpath.c makes pathkeys before it ever does this:
>
> index_is_ordered ?
> ForwardScanDirection :
> NoMovementScanDirection,
>
> and nothing depends on that later either. So I think we could
> simplify this to something like "indexscandir is either
> ForwardScanDirection or BackwardScanDirection. (Unordered
> index types need not support BackwardScanDirection.)"
>
I also did what I *think* Tom is suggesting here -- make index scan's
scan direction always forward or backward...
Maybe the set should be two patches...dunno.
- Melanie
Attachment | Content-Type | Size |
---|---|---|
v1-0001-Remove-NoMovementScanDirection-inconsistencies.patch | text/x-patch | 12.9 KB |
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