Fix representation of hash keys in Hash/HashJoin nodes.

In 5f32b29c1819 I changed the creation of HashState.hashkeys to
actually use HashState as the parent (instead of HashJoinState, which
was incorrect, as they were executed below HashState), to fix the
problem of hashkeys expressions otherwise relying on slot types
appropriate for HashJoinState, rather than HashState as would be
correct. That reliance was only introduced in 12, which is why it
previously worked to use HashJoinState as the parent (although I'd be
unsurprised if there were problematic cases).

Unfortunately that's not a sufficient solution, because before this
commit, the to-be-hashed expressions referenced inner/outer as
appropriate for the HashJoin, not Hash. That didn't have obvious bad
consequences, because the slots containing the tuples were put into
ecxt_innertuple when hashing a tuple for HashState (even though Hash
doesn't have an inner plan).

There are less common cases where this can cause visible problems
however (rather than just confusion when inspecting such executor
trees). E.g. "ERROR: bogus varno: 65000", when explaining queries
containing a HashJoin where the subsidiary Hash node's hash keys
reference a subplan. While normally hashkeys aren't displayed by
EXPLAIN, if one of those expressions references a subplan, that
subplan may be printed as part of the Hash node - which then failed
because an inner plan was referenced, and Hash doesn't have that.

It seems quite possible that there's other broken cases, too.

Fix the problem by properly splitting the expression for the HashJoin
and Hash nodes at plan time, and have them reference the proper
subsidiary node. While other workarounds are possible, fixing this
correctly seems easy enough. It was a pretty ugly hack to have
ExecInitHashJoin put the expression into the already initialized
HashState, in the first place.

I decided to not just split inner/outer hashkeys inside
make_hashjoin(), but also to separate out hashoperators and
hashcollations at plan time. Otherwise we would have ended up having
two very similar loops, one at plan time and the other during executor
startup. The work seems to more appropriately belong to plan time,
anyway.

Reported-By: Nikita Glukhov, Alexander Korotkov
Author: Andres Freund
Reviewed-By: Tom Lane, in an earlier version
Discussion: https://postgr.es/m/CAPpHfdvGVegF_TKKRiBrSmatJL2dR9uwFCuR+teQ_8tEXU8mxg@mail.gmail.com
Backpatch: 12-

2 files changed, 14 insertions, 3 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 98bdcbcef5..4ec78491f6 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1852,7 +1852,6 @@ typedef struct MergeJoinState
  *
  *		hashclauses				original form of the hashjoin condition
  *		hj_OuterHashKeys		the outer hash keys in the hashjoin condition
- *		hj_InnerHashKeys		the inner hash keys in the hashjoin condition
  *		hj_HashOperators		the join operators in the hashjoin condition
  *		hj_HashTable			hash table for the hashjoin
  *								(NULL if table not built yet)
@@ -1883,7 +1882,6 @@ typedef struct HashJoinState
 	JoinState	js;				/* its first field is NodeTag */
 	ExprState  *hashclauses;
 	List	   *hj_OuterHashKeys;	/* list of ExprState nodes */
-	List	   *hj_InnerHashKeys;	/* list of ExprState nodes */
 	List	   *hj_HashOperators;	/* list of operator OIDs */
 	List	   *hj_Collations;
 	HashJoinTable hj_HashTable;
@@ -2222,7 +2220,6 @@ typedef struct HashState
 	PlanState	ps;				/* its first field is NodeTag */
 	HashJoinTable hashtable;	/* hash table for the hashjoin */
 	List	   *hashkeys;		/* list of ExprState nodes */
-	/* hashkeys is same as parent's hj_InnerHashKeys */
 
 	SharedHashInfo *shared_info;	/* one entry per worker */
 	HashInstrumentation *hinstrument;	/* this worker's entry */
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 70f8b8e22b..8e6594e355 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -737,6 +737,14 @@ typedef struct HashJoin
 {
 	Join		join;
 	List	   *hashclauses;
+	List	   *hashoperators;
+	List	   *hashcollations;
+
+	/*
+	 * List of expressions to be hashed for tuples from the outer plan, to
+	 * perform lookups in the hashtable over the inner plan.
+	 */
+	List	   *hashkeys;
 } HashJoin;
 
 /* ----------------
@@ -899,6 +907,12 @@ typedef struct GatherMerge
 typedef struct Hash
 {
 	Plan		plan;
+
+	/*
+	 * List of expressions to be hashed for tuples from Hash's outer plan,
+	 * needed to put them into the hashtable.
+	 */
+	List	   *hashkeys;		/* hash keys for the hashjoin condition */
 	Oid			skewTable;		/* outer join key's table OID, or InvalidOid */
 	AttrNumber	skewColumn;		/* outer join key's column #, or zero */
 	bool		skewInherit;	/* is outer join rel an inheritance tree? */