Horton

Re: Removing unneeded self joins

jian he <jian.universality@gmail.com>

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From: jian he <jian.universality@gmail.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Andrei Lepikhov <a.lepikhov@postgrespro.ru>, Richard Guo <guofenglinux@gmail.com>, 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>
Date: 2024-07-04T08:40:00Z
Lists: pgsql-hackers

Commits

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  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 Thu, Jul 4, 2024 at 11:04 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
>
> On Thu, Jul 4, 2024 at 5:15 AM jian he <jian.universality@gmail.com> wrote:
> > in remove_self_join_rel, i have
> > ```ChangeVarNodes((Node *) root->parse, toRemove->relid, toKeep->relid, 0);```
> > which will change the joinlist(RangeTblRef)  from (1,2)  to (2,2).
> > Immediately after this call, I wrote a function (restore_rangetblref)
> > to restore the joinlist as original (1,2).
> > then remove_rel_from_joinlist won't error out.
> > see remove_self_join_rel, restore_rangetblref.
>
> Thank you, now this is clear.  Could we add additional parameters to
> ChangeVarNodes() instead of adding a new function which reverts part
> of changes.
>

I didn't dare to. we have 42 occurrences of ChangeVarNodes.
adding a parameter to it only for one location seems not intuitive.

Now I have tried.
changing to
`ChangeVarNodes(Node *node, int rt_index, int new_index, int
sublevels_up, bool change_RangeTblRef)`

/* Replace varno in all the query structures */
ChangeVarNodes((Node *) root->parse, toRemove->relid, toKeep->relid, 0, false);
```

it seems to work, pass the regression test.
```ChangeVarNodes((Node *) root->parse, toRemove->relid,
toKeep->relid, 0, false);```
is in remove_self_join_rel, remove_self_joins_one_group,
remove_self_joins_recurse.
all other places are ```ChangeVarNodes((Node *) root->parse,
toRemove->relid, toKeep->relid, 0, true);```
so ChangeVarNodes add a parameter will only influence the SJE feature.


I also tried, save to a temp list, but it did not work.
original_fromlist = list_copy_deep(root->parse->jointree->fromlist);
/* Replace varno in all the query structures */
ChangeVarNodes((Node *) root->parse, toRemove->relid, toKeep->relid, 0);
root->parse->jointree->fromlist = list_copy(original_fromlist);