Re: [PATCH] Keeps tracking the uniqueness with UniqueKey

+
+    foreach(lc,  unionrel->reltarget->exprs)
+    {
+        exprs = lappend(exprs, lfirst(lc));
+        colnos = lappend_int(colnos, i);
+        i++;
+    }

This should be only possible when it's not UNION ALL. We should add some assert
or protection for that.

OK, actually I called this function in generate_union_paths. which handle

UNION case only.  I will add the Assert anyway. 

 

+
+    /* Fast path */
+    if (innerrel->uniquekeys == NIL || outerrel->uniquekeys == NIL)
+        return;
+
+    outer_is_onerow = relation_is_onerow(outerrel);
+    inner_is_onerow = relation_is_onerow(innerrel);
+
+    outerrel_ukey_ctx = initililze_uniquecontext_for_joinrel(joinrel,
outerrel);
+    innerrel_ukey_ctx = initililze_uniquecontext_for_joinrel(joinrel,
innerrel);
+
+    clause_list = gather_mergeable_joinclauses(joinrel, outerrel, innerrel,
+                                               restrictlist, jointype);

Something similar happens in select_mergejoin_clauses().

I didn't realized this before.  I will refactor this code accordingly if necessary

after reading that. 

 

At least from the
first reading of this patch, I get an impression that all these functions which
are going through clause lists and index lists should be merged into other
functions which go through these lists hunting for some information useful to
the optimizer. 

+
+
+    if (innerrel_keeps_unique(root, outerrel, innerrel, clause_list, false))
+    {
+        foreach(lc, innerrel_ukey_ctx)
+        {
+            UniqueKeyContext ctx = (UniqueKeyContext)lfirst(lc);
+            if (!list_is_subset(ctx->uniquekey->exprs,
joinrel->reltarget->exprs))
+            {
+                /* The UniqueKey on baserel is not useful on the joinrel */

A joining relation need not be a base rel always, it could be a join rel as
well.

good catch. 

 

+                ctx->useful = false;
+                continue;
+            }
+            if ((jointype == JOIN_LEFT || jointype == JOIN_FULL) &&
!ctx->uniquekey->multi_nullvals)
+            {
+                /* Change the multi_nullvals to true at this case */

Need a comment explaining this. Generally, I feel, this and other functions in
this file need good comments explaining the logic esp. "why" instead of "what".

 

Exactly. 

Will continue reviewing your new set of patches as time permits.

Thank you!  Actually there is no big difference between v6 and v7 regarding the

 UniqueKey part except 2 bug fix.  However v7 has some more documents, 

comments improvement and code refactor/split, which may be helpful

for review. You may try v7 next time if v8 has not come yet:)