Re: Removing unneeded self joins

Thomas Munro <thomas.munro@enterprisedb.com>

From: Thomas Munro <thomas.munro@enterprisedb.com>
To: Alexander Kuzmenkov <a.kuzmenkov@postgrespro.ru>
Cc: David Rowley <david.rowley@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-07-29T10:42:32Z
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. Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination

  2. Put enable_self_join_elimination into postgresql.conf.sample

  3. Get rid of ojrelid local variable in remove_rel_from_query()

  4. Implement Self-Join Elimination

  5. Revert: Remove useless self-joins

  6. Replace lateral references to removed rels in subqueries

  7. Replace relids in lateral subquery parse tree during SJE

  8. Forbid SJE with result relation

  9. Fix misuse of RelOptInfo.unique_for_rels cache by SJE

  10. Replace the relid in some missing fields during SJE

  11. Revert 56-bit relfilenode change and follow-up commits.

  12. Stabilize timetz test across DST transitions.

  13. Speed up finding EquivalenceClasses for a given set of rels

  14. Fix mark-and-restore-skipping test case to not be a self-join.

On Sat, Jul 28, 2018 at 12:26 AM, Alexander Kuzmenkov
<a.kuzmenkov@postgrespro.ru> wrote:
> Here is a current version of the patch, still rather experimental.

Hi Alexander,

The eval-qual-plan isolation test is failing:

- checking       1050           checking       600
+ checking       600            checking       600

That's the result of a self join with EPQ on one side of the join:

        SELECT * FROM accounts a1, accounts a2
          WHERE a1.accountid = a2.accountid
          FOR UPDATE OF a1;

I think you need to disable the optimisation when there is a locking
clause on one side.  Maybe it could be allowed if it's on both sides?
Not sure.

+ Assert(is_opclause(rinfo->clause));
+ Expr *leftOp = (Expr *) get_leftop(rinfo->clause);

You can't declare a variable here in C89.

-- 
Thomas Munro
http://www.enterprisedb.com