Horton

Re: Extended Statistics set/restore/clear functions.

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: jian he <jian.universality@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, pgsql-hackers@lists.postgresql.org
Date: 2025-02-20T04:43:16Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add test doing some cloning of extended statistics data

  2. Add test for pg_restore_extended_stats() with multiranges

  3. Add support for "mcv" in pg_restore_extended_stats()

  4. Include extended statistics data in pg_dump

  5. Add support for "dependencies" in pg_restore_extended_stats()

  6. Add test for MAINTAIN permission with pg_restore_extended_stats()

  7. Add pg_restore_extended_stats()

  8. Add routine to free MCVList

  9. Improve pg_clear_extended_stats() with incorrect relation/stats combination

  10. Add pg_clear_extended_stats()

  11. Introduce routines to validate and free MVNDistinct and MVDependencies

  12. Fix typo in stat_utils.c

  13. Move attribute statistics functions to stat_utils.c

  14. Improve error messages of input functions for pg_dependencies and pg_ndistinct

  15. Improve test output of extended statistics for ndistinct and dependencies

  16. Fix some compiler warnings

  17. Add input function for data type pg_dependencies

  18. Add input function for data type pg_ndistinct

  19. Rework output format of pg_dependencies

  20. Rework output format of pg_ndistinct

  21. Fix comments of output routines for pg_ndistinct and pg_dependencies

  22. Move code specific to pg_dependencies to new file

  23. Move code specific to pg_ndistinct to new file

  24. Document some structures in attribute_stats.c

  25. Fix FATAL message for invalid recovery timeline at beginning of recovery

Attachments

>
> select '{"1, 0B100101":"NaN"}'::pg_ndistinct;
>>       pg_ndistinct
>> ------------------------
>>  {"1, 37": -2147483648}
>> (1 row)
>>
>
> I think my initial reaction is to just refuse those special values, but
> I'll look into the parsing code to see what can be done.
>

I noticed that the output function for pg_ndistinct casts that value to an
integer before formatting it %d, so it's being treated as an integer even
if it is not stored as one. After some consultation with Tomas, it made the
most sense to just replicate this on the input side as well, and that is
addressed in the patches below.

I've updated and rebased the patches.

The existing pg_ndistinct and pg_dependences formats were kept as-is. The
formats are clumsy, more processing-friendly formats would be easier, but
the need for such processing is minimal bordering on theoretical, so there
is little impact in keeping the historical format.

There are now checks to ensure that the pg_ndistinct or pg_dependencies
value assigned to an extended statistics object actually makes sense for
that object. What this amounts to is checking that for every attnum cited,
the positive attnums are also ones found the in the stxkeys of the
pg_statistic_ext tuple, and the negative attnums correspond do not exceed
the number of expressions in the attnum. In other words, if the stats
object has no expressions in it, then no negative numbers will be accepted,
if it has 2 expressions than any value -3 or lower will be rejected, etc.

All patches rebased to 71f17823ba010296da9946bd906bb8bcad6325bc.