From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
---|---|
To: | Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> |
Cc: | Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Tomas Vondra <tv(at)fuzzy(dot)cz>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Subject: | Re: Can rs_cindex be < 0 for bitmap heap scans? |
Date: | 2024-12-18 23:18:25 |
Message-ID: | CAAKRu_ae8g2B1NOv+w7oyAPhCen4cJ3cNxNj8syEDV0yMV1M3Q@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Dec 18, 2024 at 3:13 PM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> option 1:
> most straightforward fix
>
> diff --git a/src/backend/access/heap/heapam_handler.c
> b/src/backend/access/heap/heapam_handler.c
> index d0e5922eed7..fa03bedd4b8 100644
> --- a/src/backend/access/heap/heapam_handler.c
> +++ b/src/backend/access/heap/heapam_handler.c
> @@ -2577,6 +2577,11 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
>
> if (scan->rs_flags & SO_ALLOW_PAGEMODE)
> {
> + int start, end;
> +
> + if (hscan->rs_ntuples == 0)
> + return false;
> +
> /*
> * In pageatatime mode, heap_prepare_pagescan() already did visibility
> * checks, so just look at the info it left in rs_vistuples[].
> @@ -2586,8 +2591,8 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
> * in increasing order, but it's not clear that there would be enough
> * gain to justify the restriction.
> */
> - int start = 0,
> - end = hscan->rs_ntuples - 1;
> + start = 0;
> + end = hscan->rs_ntuples - 1;
>
> while (start <= end)
> {
>
> option 2:
> change the binary search code a bit more but avoid the extra branch
> introduced by option 1.
>
> diff --git a/src/backend/access/heap/heapam_handler.c
> b/src/backend/access/heap/heapam_handler.c
> index d0e5922eed7..c8e25bdd197 100644
> --- a/src/backend/access/heap/heapam_handler.c
> +++ b/src/backend/access/heap/heapam_handler.c
> @@ -2586,18 +2586,17 @@ SampleHeapTupleVisible(TableScanDesc scan,
> Buffer buffer,
> * in increasing order, but it's not clear that there would be enough
> * gain to justify the restriction.
> */
> - int start = 0,
> - end = hscan->rs_ntuples - 1;
> + uint32 start = 0, end = hscan->rs_ntuples;
>
> - while (start <= end)
> + while (start < end)
> {
> - int mid = (start + end) / 2;
> + int mid = (start + end) / 2;
> OffsetNumber curoffset = hscan->rs_vistuples[mid];
>
> if (tupoffset == curoffset)
> return true;
> else if (tupoffset < curoffset)
> - end = mid - 1;
> + end = mid;
> else
> start = mid + 1;
> }
I pushed the straightforward option for now so that it's fixed.
- Melanie
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