Horton

Re: Statistics Import and Export: difference in statistics dumped

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

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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Corey Huinker <corey.huinker@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Michael Paquier <michael@paquier.xyz>, Nathan Bossart <nathandbossart@gmail.com>, Bruce Momjian <bruce@momjian.us>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Magnus Hagander <magnus@hagander.net>, Stephen Frost <sfrost@snowman.net>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Alvaro Herrera <alvherre@alvh.no-ip.org>, jian he <jian.universality@gmail.com>
Date: 2025-03-04T04:58:16Z
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. 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 Tue, Mar 4, 2025 at 6:25 AM Jeff Davis <pgsql@j-davis.com> wrote:
>
> On Mon, 2025-03-03 at 22:04 +0530, Ashutosh Bapat wrote:
> > But while we have hold of reltuples wasting a chance to
> > update it in pg_class does not look right to me.
>
> To me, autovacuum=off is a pretty clear signal that the user doesn't
> want this kind of side-effect to happen. Am I missing something?

Documentation of autovacuum says "Controls whether the server should
run the autovacuum launcher daemon." It doesn't talk about updates
happening as a side-effect. With autovacuum there is an extra scan and
resources are consumed but with index creation all that cost is
already paid. I wouldn't compare those two.

The case with IsBinaryUpdate is straight, statistics is not updated
only when run in binary upgrade mode. If we could devise a way to not
update statistics only when the index is created as part of restoring
a dump, that will be easily acceptable. But I don't know

>
> > I think the solution should be on the pg_dump/restore side and not on
> > the server side.
>
> What solution are you suggesting? The only one that comes to mind is
> moving everything to SECTION_POST_DATA, which is possible, but it seems
> like a big design change to satisfy a small detail.

We don't have to do that. We can manage it by making statistics of
index dependent upon the indexes on the table. As far as dump is
concerned, they are dependent since index creation rewrites the
statistics so we would like to add statistics after index creation.
For that we will need to track the statistics dumpable object in the
TableInfo. When adding indexes to TableInfo in getIndexes, we add
dependency between the index and the table statistics. The dependency
based sorting will automatically take care ordering statistics objects
after all the index objects and thus print it after all CREATE INDEX
commands. I have not tried to code this. Do you see any problems with
that?

--
Best Wishes,
Ashutosh Bapat