Horton

Re: Statistics Import and Export

Stephen Frost <sfrost@snowman.net>

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From: Stephen Frost <sfrost@snowman.net>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Corey Huinker <corey.huinker@gmail.com>, 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: 2024-03-30T00:54:20Z
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.

Greetings,

On Fri, Mar 29, 2024 at 19:35 Jeff Davis <pgsql@j-davis.com> wrote:

> On Fri, 2024-03-29 at 18:02 -0400, Stephen Frost wrote:
> > I’d certainly think “with stats” would be the preferred default of
> > our users.
>
> I'm concerned there could still be paths that lead to an error. For
> pg_restore, or when loading a SQL file, a single error isn't fatal
> (unless -e is specified), but it still could be somewhat scary to see
> errors during a reload.


I understand that point.

Also, it's new behavior, so it may cause some minor surprises, or there
> might be minor interactions to work out. For instance, dumping stats
> doesn't make a lot of sense if pg_upgrade (or something else) is just
> going to run analyze anyway.


But we don’t expect anything to run analyze … do we?  So I’m not sure why
it makes sense to raise this as a concern.

What do you think about starting off with it as non-default, and then
> switching it to default in 18?


What’s different, given the above arguments, in making the change with 18
instead of now?  I also suspect that if we say “we will change the default
later” … that later won’t ever come and we will end up making our users
always have to remember to say “with-stats” instead.

The stats are important which is why the effort is being made in the first
place. If just doing an analyze after loading the data was good enough then
this wouldn’t be getting worked on.

Independently, I had a thought around doing an analyze as the data is being
loaded .. but we can’t do that for indexes (but we could perhaps analyze
the indexed values as we build the index..).  This works when we do a
truncate or create the table in the same transaction, so we would tie into
some of the existing logic that we have around that.  Would also adjust
COPY to accept an option that specifies the anticipated number of rows
being loaded (which we can figure out during the dump phase reasonably..).
Perhaps this would lead to a pg_dump option to do the data load as a
transaction with a truncate before the copy (point here being to be able to
still do parallel load while getting the benefits from knowing that we are
completely reloading the table). Just some other thoughts- which I don’t
intend to take away from the current effort at all, which I see as valuable
and should be enabled by default.

Thanks!

Stephen

>