Re: Removing unneeded self joins

Noah Misch <noah@leadboat.com>

From: Noah Misch <noah@leadboat.com>

To: Richard Guo <guofenglinux@gmail.com>, Andrei Lepikhov <a.lepikhov@postgrespro.ru>, Alexander Korotkov <aekorotkov@gmail.com>

Cc: Alexander Lakhin <exclusion@gmail.com>, "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>

Date: 2024-02-24T05:12:05Z

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 Sat, Feb 24, 2024 at 12:36:59AM +0200, Alexander Korotkov wrote:
> On Thu, Feb 22, 2024 at 10:51 AM Andrei Lepikhov <a.lepikhov@postgrespro.ru> wrote:
> > On 21/2/2024 14:26, Richard Guo wrote:
> > > I think the right fix for these issues is to introduce a new element
> > > 'sublevels_up' in ReplaceVarnoContext, and enhance replace_varno_walker
> > > to 1) recurse into subselects with sublevels_up increased, and 2)
> > > perform the replacement only when varlevelsup is equal to sublevels_up.
> > This code looks good. No idea how we have lost it before.
> 
> Thanks to Richard for the patch and to Andrei for review.  I also find
> code looking good.  Pushed with minor edits from me.

I feel this, commit 466979e, misses a few of our project standards:

- The patch makes many non-whitespace changes to existing test queries.  This
  makes it hard to review the consequences of the non-test part of the patch.
  Did you minimize such edits?  Of course, not every such edit is avoidable.

- The commit message doesn't convey whether this is refactoring or is a bug
  fix.  This makes it hard to write release notes, among other things.  From
  this mailing list thread, it gather it's a bug fix in 489072ab7a, hence
  v17-specific.  The commit message for 489072ab7a is also silent about that
  commit's status as refactoring or as a bug fix.

- Normally, I could answer the previous question by reading the test case
  diffs.  However, in addition to the first point about non-whitespace
  changes, the first three join.sql patch hunks just change whitespace.
  Worse, since they move line breaks, "git diff -w" doesn't filter them out.

To what extent are those community standards vs. points of individual
committer preference?  Please tell me where I'm wrong here.