Horton

Re: Statistics Import and Export

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, Bruce Momjian <bruce@momjian.us>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2023-12-28T17:28:06Z
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 Wed, Dec 27, 2023 at 10:10 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Corey Huinker <corey.huinker@gmail.com> writes:
> > Export functions was my original plan, for simplicity, maintenance, etc,
> > but it seemed like I'd be adding quite a few functions, so the one view
> > made more sense for an initial version. Also, I knew that pg_dump or some
> > other stats exporter would have to inline the guts of those functions
> into
> > queries for older versions, and adapting a view definition seemed more
> > straightforward for the reader than function definitions.
>
> Hmm, I'm not sure we are talking about the same thing at all.
>

Right, I was conflating two things.


>
> What I am proposing is *import* functions.  I didn't say anything about
> how pg_dump obtains the data it prints; however, I would advocate that
> we keep that part as simple as possible.  You cannot expect export
> functionality to know the requirements of future server versions,
> so I don't think it's useful to put much intelligence there.
>

True, but presumably you'd be using the pg_dump/pg_upgrade of that future
version to do the exporting, so the export format would always be tailored
to the importer's needs.


>
> So I think pg_dump should produce a pretty literal representation of
> what it finds in the source server's catalog, and then rely on the
> import functions in the destination server to make sense of that
> and do whatever slicing-n-dicing is required.
>

Obviously it can't be purely literal, as we have to replace the oid values
with whatever text representation we feel helps us carry forward. In
addition, we're setting the number of tuples and number of pages directly
in pg_class, and doing so non-transactionally just like ANALYZE does. We
could separate that out into its own import function, but then we're
locking every relation twice, once for the tuples/pages and once again for
the pg_statistic import.

My current line of thinking was that the stats import call, if enabled,
would immediately follow the CREATE statement of the object itself, but
that requires us to have everything we need to know for the import passed
into the import function, so we'd be needing a way to serialize _that_. If
you're thinking that we have one big bulk stats import, that might work,
but it also means that we're less tolerant of failures in the import step.