Horton

Re: Statistics Import and Export

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>
Cc: Corey Huinker <corey.huinker@gmail.com>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, 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>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, alvherre@alvh.no-ip.org
Date: 2025-02-24T18:42:40Z
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 Mon, 2025-02-24 at 12:50 -0500, Tom Lane wrote:
> Also, while working on the attached, I couldn't help forming the
> opinion that we'd be better off to nuke pg_set_attribute_stats()
> from orbit and require people to use pg_restore_attribute_stats().

I had intended the pg_set variants to be useful for ad-hoc stats
hacking (e.g. for reproducing a plan or for testing the optimizer). For
those use cases, the following differences seem nice:

  1. named arguments are easier to write ad-hoc than lining up the
parameters in pairs
  2. elevel=ERROR makes more sense than WARNING for that kind of use
case.
  3. for relation stats, we don't want in-place updates, because you
want ROLLBACK to work

Those seemed different enough from the restore case that another entry
point made sense to me.

> pg_set_attribute_stats() would be fine if we had a way to force
> people to call it with only named-argument notation, but we don't.
> So I'm afraid that its existence will encourage people to rely
> on a specific parameter order, and then they'll whine if we
> add/remove/reorder parameters, as indeed I had to do below.

That's a good point that I hadn't considered, so perhaps we can't solve
problem #1. The other two problems might be solvable though:

  * To avoid in-place updates I think we do need a separate function,
at least for relation stats (attribute stats never do in-place
updates). We could potentially have another name/value pair to choose,
but it's impossible to choose a reasonable default: if "inplace" is the
default, that means the user would need to opt-out of it for ROLLBACK
to work; if "mvcc" is the default, that means pg_dump would need to
choose "inplace", and I don't think pg_dump should be making those
kinds of decisions.

  * The elevel=ERROR is not terribly important, so perhaps we can just
always do elevel=WARNING. If we did try to present it as an option,
then that presents the same problems as an "inplace" option.

So perhaps we can just have the pg_set variants set elevel=ERROR and
inplace=false, and otherwise be identical to the pg_restore variants?

Regards,
	Jeff Davis