Horton

Re: Statistics Import and Export

Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>

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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Corey Huinker <corey.huinker@gmail.com>, Magnus Hagander <magnus@hagander.net>, Jeff Davis <pgsql@j-davis.com>, Stephen Frost <sfrost@snowman.net>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>
Date: 2024-04-05T06:09:57Z
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. Change pg_dump default for statistics export.

  2. pg_dump: Adjust reltuples from 0 to -1 for dumps of older versions.

  3. vacuumdb: Don't skip empty relations in --missing-stats-only mode.

  4. pg_dump: Fix query for gathering attribute stats on older versions.

  5. Prevent redeclaration of typedef TocEntry.

  6. Remove unused function parameters in pg_backup_archiver.c.

  7. pg_dump: Retrieve attribute statistics in batches.

  8. pg_dump: Reduce memory usage of dumps with statistics.

  9. Skip second WriteToc() call for custom-format dumps without data.

  10. Add relallfrozen to pg_dump statistics.

  11. Matview statistics depend on matview data.

  12. Add pg_dump --with-{schema|data|statistics} options.

  13. Stats: use schemaname/relname instead of regclass.

  14. CREATE INDEX: do update index stats if autovacuum=off.

  15. Don't convert to and from floats in pg_dump.

  16. CREATE INDEX: don't update table stats if autovacuum=off.

  17. Organize and deduplicate statistics import tests.

  18. Address stats export review comments.

  19. Address stats import review comments.

  20. Add relallfrozen to pg_class

  21. Fix pg_strtof() to not crash on NULL endptr.

  22. Use attnum to identify index columns in pg_restore_attribute_stats().

  23. pg_dump: prepare attribute stats query.

  24. Avoid unnecessary relation stats query in pg_dump.

  25. Remove redundant pg_set_*_stats() variants.

  26. Do not use in-place updates for statistics import.

  27. Fix confusion about data type of pg_class.relpages and relallvisible.

  28. Documentation fixups for dumping statistics.

  29. Trial fix for old cross-version upgrades.

  30. Transfer statistics during pg_upgrade.

  31. Lock table in ShareUpdateExclusive when importing index stats.

  32. Use in-place updates for pg_restore_relation_stats().

  33. Improve error message for replication of generated columns.

  34. pg_dump: Add dumpSchema and dumpData derivative flags.

  35. Disallow modifying statistics on system columns.

  36. Add missing CommandCounterIncrement() in stats import functions.

  37. Add functions pg_restore_relation_stats(), pg_restore_attribute_stats().

  38. Documentation fixup.

  39. Add functions pg_set_attribute_stats() and pg_clear_attribute_stats().

  40. Change pg_*_relation_stats() functions to return type to void.

  41. Disable autovacuum for tables in stats import tests.

  42. Allow pg_set_relation_stats() to set relpages to -1.

  43. Fixup for pg_set_relation_stats().

  44. Create functions pg_set_relation_stats, pg_clear_relation_stats.

  45. Add memory/disk usage for Window aggregate nodes in EXPLAIN.

  46. Improve performance of dumpSequenceData().

  47. Add INJECTION_POINT_CACHED() to run injection points directly from cache

  48. Improve performance of binary_upgrade_set_pg_class_oids().

  49. Improve assertion in mdwritev()

  50. CREATE INDEX: do not update stats during binary upgrade.

  51. Redefine pg_class.reltuples to be -1 before the first VACUUM or ANALYZE.

On Fri, Apr 5, 2024 at 10:07 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> writes:
> > I read that discussion, and it may be ok for pg_upgrade/pg_dump usecase
> and
> > maybe also for IMPORT foreign schema where the SQL is generated by
> > PostgreSQL itself. But not for simulating statistics. In that case, if
> the
> > function happily installs statistics cooked by the user and those aren't
> > used anywhere, users may be misled by the plans that are generated
> > subsequently. Thus negating the very purpose of simulating
> > statistics.
>
> I'm not sure what you think the "purpose of simulating statistics" is,
> but it seems like you have an extremely narrow-minded view of it.
> I think we should allow injecting any stats that won't actively crash
> the backend.  Such functionality could be useful for stress-testing
> the planner, for example, or even just to see what it would do in
> a situation that is not what you have.
>

My reply was in the following context

> For a partitioned table this value has to be true. For a normal table when
>> setting this value to true, it should at least make sure that the table has
>> at least one child. Otherwise it should throw an error. Blindly accepting
>> the given value may render the statistics unusable. Prologue of the
>> function needs to be updated accordingly.
>>
>
> I can see rejecting non-inherited stats for a partitioned table. The
> reverse, however, isn't true, because a table may end up being inherited by
> another, so those statistics may be legit. Having said that, a great deal
> of the data validation I was doing was seen as unnecessary, so I' not sure
> where this check would fall on that line. It's a trivial check if we do add
> it.
>

If a user installs inherited stats for a non-inherited table by accidently
passing true to the corresponding argument, those stats won't be even used.
The user wouldn't know that those stats are not used. Yet, they would think
that any change in the plans is the result of their stats. So whatever
simulation experiment they are running would lead to wrong conclusions.
This could be easily avoided by raising an error. Similarly for installing
non-inherited stats for a partitioned table. There might be other scenarios
where the error won't be required.

-- 
Best Wishes,
Ashutosh Bapat