Horton

Re: Statistics Import and Export

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, Corey Huinker <corey.huinker@gmail.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2023-12-26T19:19:04Z
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.

Bruce Momjian <bruce@momjian.us> writes:
> I think we need a robust API to handle two cases:

> *  changes in how we store statistics
> *  changes in how how data type values are represented in the statistics

> We have had such changes in the past, and I think these two issues are
> what have prevented import/export of statistics up to this point.
> Developing an API that doesn't cleanly handle these will cause long-term
> pain.

Agreed.

> In summary, I think we need an SQL-level command for this.

I think a SQL command is an actively bad idea.  It'll just add development
and maintenance overhead that we don't need.  When I worked on this topic
years ago at Salesforce, I had things set up with simple functions, which
pg_dump would invoke by writing more or less

	SELECT pg_catalog.load_statistics(....);

This has a number of advantages, not least of which is that an extension
could plausibly add compatible functions to older versions.  The trick,
as you say, is to figure out what the argument lists ought to be.
Unfortunately I recall few details of what I wrote for Salesforce,
but I think I had it broken down in a way where there was a separate
function call occurring for each pg_statistic "slot", thus roughly

load_statistics(table regclass, attname text, stakind int, stavalue ...);

I might have had a separate load_statistics_xxx function for each
stakind, which would ease the issue of deciding what the datatype
of "stavalue" is.  As mentioned already, we'd also need some sort of
version identifier, and we'd expect the load_statistics() functions
to be able to transform the data if the old version used a different
representation.  I agree with the idea that an explicit representation
of the source table attribute's type would be wise, too.

			regards, tom lane