Horton

Re: PG 18 release notes draft committed

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL-development <pgsql-hackers@lists.postgresql.org>
Date: 2025-05-23T02:24:51Z
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. doc PG 18 relnotes: add AFTER trigger user change item

  2. doc PG 18 relnotes: modify async I/O item for other improvements

  3. doc PG 18 relnotes: split apart log_connections item

  4. doc PG 18 relnotes: move ANALYZE item,split ANALYZE/EXPLAIN item

  5. doc PG 18 relnotes: clarify multiplication item

  6. doc PG 18 relnotes: add removal details to MD5 item

  7. doc PG 18 relnotes: fix markup

  8. doc PG 18 relnotes: clarify btree skip-scan item

  9. doc PG 18 relnotes: update to current

  10. doc PG 18 relnotes: adjust CREATE SUBSCRIPTION attribution

  11. doc PG 18 relnotes: clarify btree skip scan item

  12. doc PG 18 relnotes: mv. hash joins and GROUP BY item to General

  13. Add support for runtime arguments in injection points

  14. doc PG 18 relnotes: fix missing parens for crc32c()

  15. PG 18 relnotes: adjust RETURNING new/old item

  16. doc PG 18 relnotes: adjust pg_log_backend_memory_contexts()

  17. doc PG 18 relnotes: add pg_log_backend_memory_contexts() mention

  18. doc PG 18 relnotes: adjust pgbench per-script reporting item

  19. doc PG 18 relnotes: mention GROUP SET fixes

  20. doc PG 18 relnotes: adjust partition planning item

  21. doc PG 18 relnotes: small adjustments regarding options

  22. doc PG 18 relnotes: move partition locking item to General Perf

  23. doc PG 18 relnotes: adjust partition items

  24. doc PG 18 relnotes: reword OAuth item

  25. doc PG 18 relnotes: add mention of pg_stat_reset_backend_stats()

  26. doc PG 18 relnotes: adjust hash item

  27. doc PG 18 relnotes: split partition optimizer item into two

  28. doc PG 18 relnotes: adjust COPY and REJECT_LIMIT items

  29. doc PG 18 relnotes: move and clarify constraint items

  30. doc PG 18 relnotes: add commit for cancel key and protocol neg.

  31. doc PG 18 relnotes: fix libpq wording

  32. doc PG 18 relnotes: add GROUP BY column elimination item

  33. doc PG 18 relnotes: move protocol version item to "server"

  34. doc PG 18 relnotes: adjust libpq trace & potocol version items

  35. doc PG 18 relnotes: reword and reorder items

  36. doc: Fix memory context level in pg_log_backend_memory_contexts() example.

  37. Make levels 1-based in pg_log_backend_memory_contexts()

  38. Introduce file_copy_method setting.

  39. libpq: Handle NegotiateProtocolVersion message differently

  40. Add timingsafe_bcmp(), for constant-time memory comparison

  41. Optimization for lower(), upper(), casefold() functions.

  42. Fix ALTER SUBSCRIPTION ... SET PUBLICATION ... command.

  43. Add connection establishment duration logging

  44. Modularize log_connections output

  45. Ensure that AFTER triggers run as the instigating user.

  46. Detect redundant GROUP BY columns using UNIQUE indexes

  47. Move cancel key generation to after forking the backend

Attachments

On Wed, May 21, 2025 at 05:57:07PM -0400, Peter Geoghegan wrote:
> On Thu, May 1, 2025 at 10:44 PM Bruce Momjian <bruce@momjian.us> wrote:
> > I have committd the first draft of the PG 18 release notes.
> 
> I suggest that you use something like the following wording for the
> skip scan feature:
> 
> Add the "skip scan" optimization, which enables more efficient scans
> of multicolumn B-tree indexes for queries that omit an "=" condition
> on one or more prefix index columns.
> 
> This is similar to the wording that appeared in the beta1 announcement.
> 
> The term "skip scan" has significant baggage -- we need to be careful
> to not add to the confusion. There are naming conflicts, which seem
> likely to confuse some users. Various community members have in the
> past referred to a feature that MySQL calls loose index scan as skip
> scan, which seems wrong to me -- it clashes with the naming
> conventions used by other RDBMSs, for no good reason. Skip scan and
> loose index scan are in fact rather different features.
> 
> For example, TimescaleDB offers Loose index scan as part of the
> TimescaleDB Postgres extension, which (for whatever reason) they chose
> to call skip scan:
> 
> https://www.timescale.com/blog/how-we-made-distinct-queries-up-to-8000x-faster-on-postgresql
> 
> Note that loose index scan can only be used with certain kinds of
> queries involving DISTINCT or GROUP BY. Whereas skip scan (in Oracle
> and now in Postgres) can work with any query that omits one or more
> "=" conditions on a prefix index column from a multicolumn index (when
> a later index column has some condition that can be used by the scan)
> -- it doesn't have to involve aggregation. I believe that describing
> the feature along these lines will make it less likely that users will
> be confused by the apparent naming conflict.
> 
> FWIW, I don't think that it's important that the release notes point
> out that skip scan is only helpful when the leading/skipped column is
> low cardinality (though that detail is accurate).

I see your point that we are not defining what this does.  I went with
the attached text.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Do not let urgent matters crowd out time for investment in the future.