Horton

Statistics Import and Export

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: pgsql-hackers@lists.postgresql.org
Date: 2023-08-31T06:47:31Z
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

pg_stats_export is a view that aggregates pg_statistic data by relation
oid and stores all of the column statistical data in a system-indepdent
(i.e.
no oids, collation information removed, all MCV values rendered as text)
jsonb format, along with the relation's relname, reltuples, and relpages
from pg_class, as well as the schemaname from pg_namespace.

pg_import_rel_stats is a function which takes a relation oid,
server_version_num, num_tuples, num_pages, and a column_stats jsonb in
a format matching that of pg_stats_export, and applies that data to
the specified pg_class and pg_statistics rows for the relation
specified.

The most common use-case for such a function is in upgrades and
dump/restore, wherein the upgrade process would capture the output of
pg_stats_export into a regular table, perform the upgrade, and then
join that data to the existing pg_class rows, updating statistics to be
a close approximation of what they were just prior to the upgrade. The
hope is that these statistics are better than the early stages of
--analyze-in-stages and can be applied faster, thus reducing system
downtime.

The values applied to pg_class are done inline, which is to say
non-transactionally. The values applied to pg_statitics are applied
transactionally, as if an ANALYZE operation was reading from a
cheat-sheet.

This function and view will need to be followed up with corresponding
ones for pg_stastitic_ext and pg_stastitic_ext_data, and while we would
likely never backport the import functions, we can have user programs
do the same work as the export views such that statistics can be brought
forward from versions as far back as there is jsonb to store it.

While the primary purpose of the import function(s) are to reduce downtime
during an upgrade, it is not hard to see that they could also be used to
facilitate tuning and development operations, asking questions like "how
might
this query plan change if this table has 1000x rows in it?", without
actually
putting those rows into the table.