Horton

Re: Statistics Import and Export

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Bruce Momjian <bruce@momjian.us>, Tom Lane <tgl@sss.pgh.pa.us>, Nathan Bossart <nathandbossart@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>, alvherre@alvh.no-ip.org
Date: 2024-08-23T20:49:52Z
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.

Attachments

On Thu, 2024-08-15 at 20:53 -0400, Corey Huinker wrote:
> 
> >   * Remind me why the new stats completely replace the new row,
> > rather
> > than updating only the statistic kinds that are specified?
> 
> because:
> - complexity

I don't think it significantly impacts the overall complexity. We have
a ShareUpdateExclusiveLock on the relation, so there's no concurrency
to deal with, and an upsert operation is not many more lines of code.

> - we would then need a mechanism to then tell it to *delete* a
> stakind

That sounds useful regardless. I have introduced pg_clear_*_stats()
functions.

> - we'd have to figure out how to reorder the remaining stakinds, or
> spend effort finding a matching stakind in the existing row to know
> to replace it

Right. I initialized the values/nulls arrays based on the existing
tuple, if any, and created a set_stats_slot() function that searches
for either a matching stakind or the first empty slot.

> - "do what analyze does" was an initial goal and as a result many
> test cases directly compared pg_statistic rows from an original table
> to an empty clone table to see if the "copy" had fidelity.

Can't we just clear the stats first to achieve the same effect?


I have attached version 28j as one giant patch covering what was
previously 0001-0003. It's a bit rough (tests in particular need some
work), but it implelements the logic to replace only those values
specified rather than the whole tuple.

At least for the interactive "set" variants of the functions, I think
it's an improvement. It feels more natural to just change one stat
without wiping out all the others. I realize a lot of the statistics
depend on each other, but the point is not to replace ANALYZE, the
point is to experiment with planner scenarios. What do others think?

For the "restore" variants, I'm not sure it matters a lot because the
stats will already be empty. If it does matter, we could pretty easily
define the "restore" variants to wipe out existing stats when loading
the table, though I'm not sure if that's a good thing or not.

I also made more use of FunctionCallInfo structures to communicate
between functions rather than huge parameter lists. I believe that
reduced the line count substantially, and made it easier to transform
the argument pairs in the "restore" variants into the positional
arguments for the "set" variants.

Regards,
	Jeff Davis