Horton

Re: [HACKERS] PATCH: multivariate histograms and MCV lists

Dean Rasheed <dean.a.rasheed@gmail.com>

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From: Dean Rasheed <dean.a.rasheed@gmail.com>
To: David Rowley <david.rowley@2ndquadrant.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Bruce Momjian <bruce@momjian.us>, Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Mark Dilger <hornschnorter@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-17T07:46:51Z
Lists: pgsql-hackers 
On Thu, 17 Jan 2019 at 03:42, David Rowley <david.rowley@2ndquadrant.com> wrote:
> 35. The evaluation order of this macro is wrong.
>
> #define ITEM_SIZE(ndims) \
> (ndims * (sizeof(uint16) + sizeof(bool)) + 2 * sizeof(double))
>
> You'd probably want ITEM_SIZE(10) to return 170, but:
>
> select (10 * (2 + 1) + 2 * 8);
>  ?column?
> ----------
>        46
>
> Unsure why this does not cause a crash.
>

No, the code is actually correct, as explained in the comment above
it. Each item contains (ndims) copies of the uint16 index and the
boolean, but it always contains exactly 2 doubles, independent of
ndims.

> ndims should also have parenthesis around it in case someone does
> ITEM_SIZE(x + y), likewise for the other ITEM_* macros.
>

+1 on that point.

Regards,
Dean

Commits

  1. Convert pre-existing stats_ext tests to new style

  2. Add support for multivariate MCV lists

  3. Improve ANALYZE's strategy for finding MCVs.

  4. Clone extended stats in CREATE TABLE (LIKE INCLUDING ALL)

  5. Try again to fix accumulation of parallel worker instrumentation.

  6. Adjust psql \d query to avoid use of @> operator.

  7. Message style fixes

  8. Add security checks to selectivity estimation functions