Fix deletion of speculatively inserted TOAST on conflict

INSERT ..  ON CONFLICT runs a pre-check of the possible conflicting
constraints before performing the actual speculative insertion.  In case
the inserted tuple included TOASTed columns the ON CONFLICT condition
would be handled correctly in case the conflict was caught by the
pre-check, but if two transactions entered the speculative insertion
phase at the same time, one would have to re-try, and the code for
aborting a speculative insertion did not handle deleting the
speculatively inserted TOAST datums correctly.

TOAST deletion would fail with "ERROR: attempted to delete invisible
tuple" as we attempted to remove the TOAST tuples using
simple_heap_delete which reasoned that the given tuples should not be
visible to the command that wrote them.

This commit updates the heap_abort_speculative() function which aborts
the conflicting tuple to use itself, via toast_delete, for deleting
associated TOAST datums.  Like before, the inserted toast rows are not
marked as being speculative.

This commit also adds a isolationtester spec test, exercising the
relevant code path. Unfortunately 9.5 cannot handle two waiting
sessions, and thus cannot execute this test.

Reported-By: Viren Negi, Oskari Saarenmaa
Author: Oskari Saarenmaa, edited a bit by me
Bug: #14150
Discussion: <20160519123338.12513.20271@wrigleys.postgresql.org>
Backpatch: 9.5, where ON CONFLICT was introduced

2 files changed, 17 insertions, 10 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 24bd9be5e17..c63dfa0bafc 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -3335,7 +3335,7 @@ l1:
 		Assert(!HeapTupleHasExternal(&tp));
 	}
 	else if (HeapTupleHasExternal(&tp))
-		toast_delete(relation, &tp);
+		toast_delete(relation, &tp, false);
 
 	/*
 	 * Mark tuple for invalidation from system caches at next command
@@ -6057,7 +6057,8 @@ heap_finish_speculative(Relation relation, HeapTuple tuple)
  * could deadlock with each other, which would not be acceptable.
  *
  * This is somewhat redundant with heap_delete, but we prefer to have a
- * dedicated routine with stripped down requirements.
+ * dedicated routine with stripped down requirements.  Note that this is also
+ * used to delete the TOAST tuples created during speculative insertion.
  *
  * This routine does not affect logical decoding as it only looks at
  * confirmation records.
@@ -6101,7 +6102,7 @@ heap_abort_speculative(Relation relation, HeapTuple tuple)
 	 */
 	if (tp.t_data->t_choice.t_heap.t_xmin != xid)
 		elog(ERROR, "attempted to kill a tuple inserted by another transaction");
-	if (!HeapTupleHeaderIsSpeculative(tp.t_data))
+	if (!(IsToastRelation(relation) || HeapTupleHeaderIsSpeculative(tp.t_data)))
 		elog(ERROR, "attempted to kill a non-speculative tuple");
 	Assert(!HeapTupleHeaderIsHeapOnly(tp.t_data));
 
@@ -6171,7 +6172,10 @@ heap_abort_speculative(Relation relation, HeapTuple tuple)
 	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 
 	if (HeapTupleHasExternal(&tp))
-		toast_delete(relation, &tp);
+	{
+		Assert(!IsToastRelation(relation));
+		toast_delete(relation, &tp, true);
+	}
 
 	/*
 	 * Never need to mark tuple for invalidation, since catalogs don't support
diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index bbb26493717..fc4702ce6f3 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -67,7 +67,7 @@ typedef struct toast_compress_header
 #define TOAST_COMPRESS_SET_RAWSIZE(ptr, len) \
 	(((toast_compress_header *) (ptr))->rawsize = (len))
 
-static void toast_delete_datum(Relation rel, Datum value);
+static void toast_delete_datum(Relation rel, Datum value, bool is_speculative);
 static Datum toast_save_datum(Relation rel, Datum value,
 				 struct varlena * oldexternal, int options);
 static bool toastrel_valueid_exists(Relation toastrel, Oid valueid);
@@ -461,7 +461,7 @@ toast_datum_size(Datum value)
  * ----------
  */
 void
-toast_delete(Relation rel, HeapTuple oldtup)
+toast_delete(Relation rel, HeapTuple oldtup, bool is_speculative)
 {
 	TupleDesc	tupleDesc;
 	Form_pg_attribute *att;
@@ -508,7 +508,7 @@ toast_delete(Relation rel, HeapTuple oldtup)
 			if (toast_isnull[i])
 				continue;
 			else if (VARATT_IS_EXTERNAL_ONDISK(PointerGetDatum(value)))
-				toast_delete_datum(rel, value);
+				toast_delete_datum(rel, value, is_speculative);
 		}
 	}
 }
@@ -1064,7 +1064,7 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
 	if (need_delold)
 		for (i = 0; i < numAttrs; i++)
 			if (toast_delold[i])
-				toast_delete_datum(rel, toast_oldvalues[i]);
+				toast_delete_datum(rel, toast_oldvalues[i], false);
 
 	return result_tuple;
 }
@@ -1656,7 +1656,7 @@ toast_save_datum(Relation rel, Datum value,
  * ----------
  */
 static void
-toast_delete_datum(Relation rel, Datum value)
+toast_delete_datum(Relation rel, Datum value, bool is_speculative)
 {
 	struct varlena *attr = (struct varlena *) DatumGetPointer(value);
 	struct varatt_external toast_pointer;
@@ -1707,7 +1707,10 @@ toast_delete_datum(Relation rel, Datum value)
 		/*
 		 * Have a chunk, delete it
 		 */
-		simple_heap_delete(toastrel, &toasttup->t_self);
+		if (is_speculative)
+			heap_abort_speculative(toastrel, toasttup);
+		else
+			simple_heap_delete(toastrel, &toasttup->t_self);
 	}
 
 	/*