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Thread: Partial index causing wrong results to be returned on 8.1.3

Partial index causing wrong results to be returned on 8.1.3

From
Greg Sabino Mullane
Date:
I could not duplicate this on any identical database, but thought I
would report it here, just for completeness. I've tried reindexing,
vacuuming, etc. Explain plans all look normal.

Version is 8.1.3
\d bigtable
...
"bigtable_status_partial" btree (status) WHERE status::text <>
'shipped'::text
=20
=20
greg=3D> select (select count(*) from bigtable where status  =3D 'shipped')
            + (select count(*) from bigtable where status <> 'shipped')
       UNION select count(*) from bigtable;
 ?column?
----------
  1185213
  1600569
=20
greg=3D> drop index bigtable_status_partial;
=20
greg=3D> select (select count(*) from bigtable where status  =3D 'shipped')
            + (select count(*) from bigtable where status <> 'shipped')
       UNION select count(*) from bigtable;
 ?column?
----------
  1185213
(1 row)

--
Greg Sabino Mullane greg@turnstep.com
End Point Corporation
PGP Key: 0x14964AC8 200608290003
http://biglumber.com/x/web?pk=3D2529DF6AB8F79407E94445B4BC9B906714964AC8

Re: Partial index causing wrong results to be returned on 8.1.3

From
Tom Lane
Date:
Greg Sabino Mullane <greg@turnstep.com> writes:
> I could not duplicate this on any identical database, but thought I
> would report it here, just for completeness. I've tried reindexing,
> vacuuming, etc. Explain plans all look normal.

Possibly explained by this 8.1.4 fix?

2006-05-18 14:57  tgl

    * src/backend/optimizer/plan/: createplan.c (REL8_1_STABLE),
    createplan.c: When a bitmap indexscan is using a partial index, it
    is necessary to include the partial index predicate in the scan's
    "recheck condition".  Otherwise, if the scan becomes lossy for lack
    of bitmap memory, we would fail to enforce that returned rows
    satisfy the predicate.    Noted while studying bug #2441 from Arjen
    van der Meijden.

If it gives right answers after you increase work_mem sufficiently,
I'd bet on this one ...

            regards, tom lane

Re: Partial index causing wrong results to be returned on 8.1.3

From
"Greg Sabino Mullane"
Date:
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> If it gives right answers after you increase work_mem sufficiently,
> I'd bet on this one ...

That's a good bet. Changing it from 1024 to 3500 did the trick ... only
one row returned, even when using the index. Thanks very much!

- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation
PGP Key: 0x14964AC8 200608290100
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8


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