|From:||Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>|
|To:||Mark Dilger <hornschnorter(at)gmail(dot)com>|
|Cc:||Adrien Nayrat <adrien(dot)nayrat(at)dalibo(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: [HACKERS] PATCH: multivariate histograms and MCV lists|
|Views:||Raw Message | Whole Thread | Download mbox|
On 11/25/2017 05:15 PM, Mark Dilger wrote:
>> On Nov 18, 2017, at 12:28 PM, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> Attached is an updated version of the patch, adopting the psql describe
>> changes introduced by 471d55859c11b.
>> Tomas Vondra http://www.2ndQuadrant.com
>> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
> Thanks, Tomas, again for your work on this feature.
> Applying just the 0001-multivariate-MCV-lists.patch to the current master, and
> then extending the stats_ext.sql test as follows, I am able to trigger an error,
> "ERROR: operator 4294934272 is not a valid ordering operator".
Ah, that's a silly bug ...
The code assumes that VacAttrStats->extra_data is always StdAnalyzeData,
and attempts to extract the ltopr from that. But for arrays that's of
course not true (array_typanalyze uses ArrayAnalyzeExtraData instead).
The reason why this only fails after the second INSERT is that we need
at least two occurrences of a value before considering it eligible for
MCV list. So after the first INSERT we don't even call the serialize.
Attached is a fix that should resolve this in MCV lists by looking up
the operator using lookup_type_cache() when serializing the MCV.
FWIW histograms have the same issue, but on more places (not just in
serialize, but also when building the histogram).
I'll send a properly updated patch series shortly, with tests checking
correct behavior with arrays.
Thanks for the report.
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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