Re: Removing unneeded self joins

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

From: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>

To: Zhihong Yu <zyu@yugabyte.com>

Cc: Hywel Carver <hywel@skillerwhale.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>

Date: 2021-07-27T05:34:30Z

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

Attachments

v29-0001-Remove-self-joins.patch (text/x-patch)

On 7/16/21 12:28 AM, Zhihong Yu wrote:
> 
> 
> On Thu, Jul 15, 2021 at 8:25 AM Zhihong Yu <zyu@yugabyte.com 
> <mailto:zyu@yugabyte.com>> wrote:
>     bq. We can proof the uniqueness
> 
>     proof -> prove
Fixed
> 
>     1. Collect all mergejoinable join quals looks like a.x = b.x
> 
>       quals looks like -> quals which look like
> 
>     For update_ec_sources(), the variable cc is not used.
Fixed
> +   *otherjoinquals = rjoinquals;
> 
> Maybe rename rjoinquals as ojoinquals to align with the target variable 
> name.
Agree, fixed
> 
> +   int k; /* Index of kept relation */
> +   int r = -1; /* Index of removed relation */
> 
> Naming k as kept, r as removed would make the code more readable (remain 
> starts with r but has opposite meaning).
I think it is correct now: k - index of inner (keeping) relation. r - of 
outer (removing) relation.
> 
> +               if (bms_is_member(r, info->syn_righthand) &&
> +                   !bms_is_member(k, info->syn_righthand))
> +                   jinfo_check = false;
> +
> +               if (!jinfo_check)
> +                   break;
> 
> There are 4 if statements where jinfo_check is assigned false. Once 
> jinfo_check is assigned, we can break out of the loop - instead of 
> checking the remaining conditions.
Fixed
> 
> +           else if (!innerrel_is_unique(root, joinrelids, outer->relids,
> 
> nit: the 'else' is not needed since the if block above it goes to next 
> iteration of the loop.
Fixed
> 
> +           /* See for row marks. */
> +           foreach (lc, root->rowMarks)
> 
> It seems once imark and omark are set, we can come out of the loop.
Maybe you right. fixed.

-- 
regards,
Andrey Lepikhov
Postgres Professional