Horton

Re: Statistics Import and Export

Matthias van de Meent <boekewurm+postgres@gmail.com>

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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Jeff Davis <pgsql@j-davis.com>, Nathan Bossart <nathandbossart@gmail.com>, Corey Huinker <corey.huinker@gmail.com>, Magnus Hagander <magnus@hagander.net>, Stephen Frost <sfrost@snowman.net>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>
Date: 2024-04-24T19:56:15Z
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 Wed, 24 Apr 2024 at 21:31, Bruce Momjian <bruce@momjian.us> wrote:
>
> On Tue, Apr 23, 2024 at 06:33:48PM +0200, Matthias van de Meent wrote:
> > I've heard of use cases where dumping stats without data would help
> > with production database planner debugging on a non-prod system.
> >
> > Sure, some planner inputs would have to be taken into account too, but
> > having an exact copy of production stats is at least a start and can
> > help build models and alerts for what'll happen when the tables grow
> > larger with the current stats.
> >
> > As for other planner inputs: table size is relatively easy to shim
> > with sparse files; cumulative statistics can be copied from a donor
> > replica if needed, and btree indexes only really really need to
> > contain their highest and lowest values (and need their height set
> > correctly).
>
> Is it possible to prevent stats from being updated by autovacuum

You can set autovacuum_analyze_threshold and *_scale_factor to
excessively high values, which has the effect of disabling autoanalyze
until it has had similarly excessive tuple churn. But that won't
guarantee autoanalyze won't run; that guarantee only exists with
autovacuum = off.

> and other methods?

No nice ways. AFAIK there is no command (or command sequence) that can
"disable" only ANALYZE and which also guarantee statistics won't be
updated until ANALYZE is manually "re-enabled" for that table. An
extension could maybe do this, but I'm not aware of any extension
points where this would hook into PostgreSQL in a nice way.

You can limit maintenance access on the table to only trusted roles
that you know won't go in and run ANALYZE for those tables, or even
only your superuser (so only they can run ANALYZE, and have them
promise they won't). Alternatively, you can also constantly keep a
lock on the table that conflicts with ANALYZE. The last few are just
workarounds though, and not all something I'd suggest running on a
production database.

Kind regards,

Matthias van de Meent