| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
| Cc: | Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>, 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: | 2024-12-19 02:50:31 |
| Message-ID: | CAMbWs4-zobtjyuNhSaYCXmCxnk9Ok8CoQGyt_ZS+fuYCAtxhew@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Dec 19, 2024 at 8:18 AM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
> I pushed the straightforward option for now so that it's fixed.
I think this binary search code now has a risk of underflow. If 'mid'
is calculated as zero, the second 'if' branch will cause 'end' to
underflow.
Maybe we need to do something like below.
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2600,7 +2600,11 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,
if (tupoffset == curoffset)
return true;
else if (tupoffset < curoffset)
+ {
+ if (mid == 0)
+ return false;
end = mid - 1;
+ }
else
start = mid + 1;
}
Alternatively, we can revert 'start' and 'end' to signed int as they
were before.
Thanks
Richard
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