Re: Making Vars outer-join aware

Anton A. Melnikov <aamelnikov@inbox.ru>

From: "Anton A. Melnikov" <aamelnikov@inbox.ru>

To: Justin Pryzby <pryzby@telsasoft.com>, Richard Guo <guofenglinux@gmail.com>

Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@lists.postgresql.org, "Finnerty, Jim" <jfinnert@amazon.com>

Date: 2023-05-04T07:22:36Z

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 →

Re-allow INDEX_VAR as rt_index in ChangeVarNodes().
- fbf80421ead5 16.0 landed
Fix thinkos in have_unsafe_outer_join_ref; reduce to Assert check.
- f50f029c497d 16.0 landed
Invent "join domains" to replace the below_outer_join hack.
- 3bef56e11650 16.0 landed
Do assorted mop-up in the planner.
- b448f1c8d83f 16.0 landed
Make Vars be outer-join-aware.
- 2489d76c4906 16.0 landed
Invent "multibitmapsets", and use them to speed up antijoin detection.
- e9e26b5e7166 16.0 landed
Add basic regression tests for semi/antijoin recognition.
- 0043aa6b8597 16.0 landed
Improve performance of adjust_appendrel_attrs_multilevel.
- 2f17b57017e5 16.0 landed
Refactor addition of PlaceHolderVars to joinrel targetlists.
- afa0ec30bfd1 16.0 landed
Use an explicit state flag to control PlaceHolderInfo creation.
- b3ff6c742f6c 16.0 landed
Make PlaceHolderInfo lookup O(1).
- 6569ca43973b 16.0 landed

Hello!

I'm having doubts about this fix but most likely i don't understand something.
Could you help me to figure it out, please.

The thing is that for custom scan nodes as readme says:
"INDEX_VAR is abused to signify references to columns of a custom scan tuple type"
But INDEX_VAR has a negative value, so it can not be used in varnullingrels bitmapset.
And therefore this improvement seems will not work with custom scan nodes and some
extensions that use such nodes.

If i'm wrong in my doubts and bitmapset for varnullingrels is ok, may be add a check before
adjust_relid_set() call like this:

@@ -569,9 +569,10 @@ ChangeVarNodes_walker(Node *node, ChangeVarNodes_context *context)
                 {
                         if (var->varno == context->rt_index)
                                 var->varno = context->new_index;
-                       var->varnullingrels = adjust_relid_set(var->varnullingrels,
-                                                              context->rt_index,
-                                                              context->new_index);
+                       if (context->rt_index >= 0 && context->new_index >= 0)
+                               var->varnullingrels = adjust_relid_set(var->varnullingrels,
+                                                                      context->rt_index,
+

With the best wishes,

-- 
Anton A. Melnikov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company