Fix problems with cached tuple descriptors disappearing while still in use

by creating a reference-count mechanism, similar to what we did a long time
ago for catcache entries.  The back branches have an ugly solution involving
lots of extra copies, but this way is more efficient.  Reference counting is
only applied to tupdescs that are actually in caches --- there seems no need
to use it for tupdescs that are generated in the executor, since they'll go
away during plan shutdown by virtue of being in the per-query memory context.
Neil Conway and Tom Lane

Author: tglsfdc

src/backend/access/common/tupdesc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/common/tupdesc.c,v 1.116 2006/03/16 00:31:54 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/common/tupdesc.c,v 1.117 2006/06/16 18:42:21 tgl Exp $
  *
  * NOTES
  *	  some of the executor utility code such as "ExecTypeFromTL" should be
@@ -23,6 +23,7 @@
 #include "catalog/pg_type.h"
 #include "parser/parse_type.h"
 #include "utils/builtins.h"
+#include "utils/resowner.h"
 #include "utils/syscache.h"
 
 
@@ -84,6 +85,7 @@ CreateTemplateTupleDesc(int natts, bool hasoid)
 	desc->tdtypeid = RECORDOID;
 	desc->tdtypmod = -1;
 	desc->tdhasoid = hasoid;
+	desc->tdrefcount = -1;		/* assume not reference-counted */
 
 	return desc;
 }
@@ -116,6 +118,7 @@ CreateTupleDesc(int natts, bool hasoid, Form_pg_attribute *attrs)
 	desc->tdtypeid = RECORDOID;
 	desc->tdtypmod = -1;
 	desc->tdhasoid = hasoid;
+	desc->tdrefcount = -1;		/* assume not reference-counted */
 
 	return desc;
 }
@@ -214,6 +217,12 @@ FreeTupleDesc(TupleDesc tupdesc)
 {
 	int			i;
 
+	/*
+	 * Possibly this should assert tdrefcount == 0, to disallow explicit
+	 * freeing of un-refcounted tupdescs?
+	 */
+	Assert(tupdesc->tdrefcount <= 0);
+
 	if (tupdesc->constr)
 	{
 		if (tupdesc->constr->num_defval > 0)
@@ -246,12 +255,48 @@ FreeTupleDesc(TupleDesc tupdesc)
 	pfree(tupdesc);
 }
 
+/*
+ * Increment the reference count of a tupdesc, and log the reference in
+ * CurrentResourceOwner.
+ *
+ * Do not apply this to tupdescs that are not being refcounted.  (Use the
+ * macro PinTupleDesc for tupdescs of uncertain status.)
+ */
+void
+IncrTupleDescRefCount(TupleDesc tupdesc)
+{
+	Assert(tupdesc->tdrefcount >= 0);
+
+	ResourceOwnerEnlargeTupleDescs(CurrentResourceOwner);
+	tupdesc->tdrefcount++;
+	ResourceOwnerRememberTupleDesc(CurrentResourceOwner, tupdesc);
+}
+
+/*
+ * Decrement the reference count of a tupdesc, remove the corresponding
+ * reference from CurrentResourceOwner, and free the tupdesc if no more
+ * references remain.
+ *
+ * Do not apply this to tupdescs that are not being refcounted.  (Use the
+ * macro ReleaseTupleDesc for tupdescs of uncertain status.)
+ */
+void
+DecrTupleDescRefCount(TupleDesc tupdesc)
+{
+	Assert(tupdesc->tdrefcount > 0);
+
+	ResourceOwnerForgetTupleDesc(CurrentResourceOwner, tupdesc);
+	if (--tupdesc->tdrefcount == 0)
+		FreeTupleDesc(tupdesc);
+}
+
 /*
  * Compare two TupleDesc structures for logical equality
  *
  * Note: we deliberately do not check the attrelid and tdtypmod fields.
  * This allows typcache.c to use this routine to see if a cached record type
  * matches a requested type, and is harmless for relcache.c's uses.
+ * We don't compare tdrefcount, either.
  */
 bool
 equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)

src/backend/access/heap/tuptoaster.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.59 2006/03/05 15:58:21 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.60 2006/06/16 18:42:21 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -892,7 +892,10 @@ toast_flatten_tuple_attribute(Datum value,
 	 * If nothing to untoast, just return the original tuple.
 	 */
 	if (!need_change)
+	{
+		ReleaseTupleDesc(tupleDesc);
 		return value;
+	}
 
 	/*
 	 * Calculate the new size of the tuple.  Header size should not change,
@@ -929,6 +932,7 @@ toast_flatten_tuple_attribute(Datum value,
 	for (i = 0; i < numAttrs; i++)
 		if (toast_free[i])
 			pfree(DatumGetPointer(toast_values[i]));
+	ReleaseTupleDesc(tupleDesc);
 
 	return PointerGetDatum(new_data);
 }

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.184 2006/05/10 23:18:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.185 2006/06/16 18:42:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2637,6 +2637,9 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 
 		MemoryContextSwitchTo(oldCxt);
 		heap_endscan(scan);
+
+		ExecDropSingleTupleTableSlot(oldslot);
+		ExecDropSingleTupleTableSlot(newslot);
 	}
 
 	FreeExecutorState(estate);

src/backend/executor/execJunk.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.52 2006/03/05 15:58:25 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.53 2006/06/16 18:42:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -79,7 +79,7 @@ ExecInitJunkFilter(List *targetList, bool hasoid, TupleTableSlot *slot)
 	 * Use the given slot, or make a new slot if we weren't given one.
 	 */
 	if (slot)
-		ExecSetSlotDescriptor(slot, cleanTupType, false);
+		ExecSetSlotDescriptor(slot, cleanTupType);
 	else
 		slot = MakeSingleTupleTableSlot(cleanTupType);
 
@@ -150,7 +150,7 @@ ExecInitJunkFilterConversion(List *targetList,
 	 * Use the given slot, or make a new slot if we weren't given one.
 	 */
 	if (slot)
-		ExecSetSlotDescriptor(slot, cleanTupType, false);
+		ExecSetSlotDescriptor(slot, cleanTupType);
 	else
 		slot = MakeSingleTupleTableSlot(cleanTupType);
 

src/backend/executor/execMain.c

@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.270 2006/04/30 18:30:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.271 2006/06/16 18:42:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1445,9 +1445,7 @@ ExecInsert(TupleTableSlot *slot,
 			TupleTableSlot *newslot = estate->es_trig_tuple_slot;
 
 			if (newslot->tts_tupleDescriptor != slot->tts_tupleDescriptor)
-				ExecSetSlotDescriptor(newslot,
-									  slot->tts_tupleDescriptor,
-									  false);
+				ExecSetSlotDescriptor(newslot, slot->tts_tupleDescriptor);
 			ExecStoreTuple(newtuple, newslot, InvalidBuffer, false);
 			slot = newslot;
 			tuple = newtuple;
@@ -1654,9 +1652,7 @@ ExecUpdate(TupleTableSlot *slot,
 			TupleTableSlot *newslot = estate->es_trig_tuple_slot;
 
 			if (newslot->tts_tupleDescriptor != slot->tts_tupleDescriptor)
-				ExecSetSlotDescriptor(newslot,
-									  slot->tts_tupleDescriptor,
-									  false);
+				ExecSetSlotDescriptor(newslot, slot->tts_tupleDescriptor);
 			ExecStoreTuple(newtuple, newslot, InvalidBuffer, false);
 			slot = newslot;
 			tuple = newtuple;