Re: Removing unneeded self joins

David Rowley <david.rowley@2ndquadrant.com>

From: David Rowley <david.rowley@2ndquadrant.com>

To: Andres Freund <andres@anarazel.de>

Cc: Tom Lane <tgl@sss.pgh.pa.us>, Simon Riggs <simon@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Alexander Kuzmenkov <a.kuzmenkov@postgrespro.ru>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2018-05-17T01:38:50Z

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 →

Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination
- 717d0e8dd945 18.0 landed
Put enable_self_join_elimination into postgresql.conf.sample
- c2d329260cd8 18.0 landed
Get rid of ojrelid local variable in remove_rel_from_query()
- e167191dc146 18.0 landed
Implement Self-Join Elimination
- fc069a3a6319 18.0 cited
Revert: Remove useless self-joins
- d1d286d83c0e 17.0 landed
Replace lateral references to removed rels in subqueries
- 466979ef031a 17.0 landed
Replace relids in lateral subquery parse tree during SJE
- 489072ab7a9e 17.0 landed
Forbid SJE with result relation
- 8c441c082797 17.0 landed
Fix misuse of RelOptInfo.unique_for_rels cache by SJE
- 30b4955a4668 17.0 landed
Replace the relid in some missing fields during SJE
- a7928a57b9f0 17.0 landed
Revert 56-bit relfilenode change and follow-up commits.
- a448e49bcbe4 16.0 cited
Stabilize timetz test across DST transitions.
- 4a071afbd056 14.0 cited
Speed up finding EquivalenceClasses for a given set of rels
- 3373c7155350 13.0 cited
Fix mark-and-restore-skipping test case to not be a self-join.
- 24d08f3c0a1f 12.0 landed

On 17 May 2018 at 11:00, Andres Freund <andres@anarazel.de> wrote:
> Wonder if we shouldn't just cache an estimated relation size in the
> relcache entry till then. For planning purposes we don't need to be
> accurate, and usually activity that drastically expands relation size
> will trigger relcache activity before long. Currently there's plenty
> workloads where the lseeks(SEEK_END) show up pretty prominently.

While I'm in favour of speeding that up, I think we'd get complaints
if we used a stale value.  We could have uses pg_class.relpages all
along, but it would cause the planner to not work so well in face of
the relation changing size significantly between analyze runs.

FWIW the major case where that does show up is when generating a plan
for a partitioned table with many partitions then pruning all but a
few of them.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
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