v3_add_doubly_linked_count_lists.patch

diff --git a/src/backend/access/heap/rewriteheap.c b/src/backend/access/heap/rewriteheap.c
index b01b39b008..a34e9b352d 100644
--- a/src/backend/access/heap/rewriteheap.c
+++ b/src/backend/access/heap/rewriteheap.c
@@ -196,8 +196,7 @@ typedef struct RewriteMappingFile
 	TransactionId xid;			/* xid that might need to see the row */
 	int			vfd;			/* fd of mappings file */
 	off_t		off;			/* how far have we written yet */
-	uint32		num_mappings;	/* number of in-memory mappings */
-	dlist_head	mappings;		/* list of in-memory mappings */
+	dclist_head mappings;		/* list of in-memory mappings */
 	char		path[MAXPGPATH];	/* path, for error messages */
 } RewriteMappingFile;
 
@@ -864,9 +863,10 @@ logical_heap_rewrite_flush_mappings(RewriteState state)
 		Oid			dboid;
 		uint32		len;
 		int			written;
+		uint32		num_mappings = dclist_count(&src->mappings);
 
 		/* this file hasn't got any new mappings */
-		if (src->num_mappings == 0)
+		if (num_mappings == 0)
 			continue;
 
 		if (state->rs_old_rel->rd_rel->relisshared)
@@ -874,7 +874,7 @@ logical_heap_rewrite_flush_mappings(RewriteState state)
 		else
 			dboid = MyDatabaseId;
 
-		xlrec.num_mappings = src->num_mappings;
+		xlrec.num_mappings = num_mappings;
 		xlrec.mapped_rel = RelationGetRelid(state->rs_old_rel);
 		xlrec.mapped_xid = src->xid;
 		xlrec.mapped_db = dboid;
@@ -882,31 +882,30 @@ logical_heap_rewrite_flush_mappings(RewriteState state)
 		xlrec.start_lsn = state->rs_begin_lsn;
 
 		/* write all mappings consecutively */
-		len = src->num_mappings * sizeof(LogicalRewriteMappingData);
+		len = num_mappings * sizeof(LogicalRewriteMappingData);
 		waldata_start = waldata = palloc(len);
 
 		/*
 		 * collect data we need to write out, but don't modify ondisk data yet
 		 */
-		dlist_foreach_modify(iter, &src->mappings)
+		dclist_foreach_modify(iter, &src->mappings)
 		{
 			RewriteMappingDataEntry *pmap;
 
-			pmap = dlist_container(RewriteMappingDataEntry, node, iter.cur);
+			pmap = dclist_container(RewriteMappingDataEntry, node, iter.cur);
 
 			memcpy(waldata, &pmap->map, sizeof(pmap->map));
 			waldata += sizeof(pmap->map);
 
 			/* remove from the list and free */
-			dlist_delete(&pmap->node);
+			dclist_delete_from(&src->mappings, &pmap->node);
 			pfree(pmap);
 
 			/* update bookkeeping */
 			state->rs_num_rewrite_mappings--;
-			src->num_mappings--;
 		}
 
-		Assert(src->num_mappings == 0);
+		Assert(dclist_count(&src->mappings) == 0);
 		Assert(waldata == waldata_start + len);
 
 		/*
@@ -1002,8 +1001,7 @@ logical_rewrite_log_mapping(RewriteState state, TransactionId xid,
 				 LSN_FORMAT_ARGS(state->rs_begin_lsn),
 				 xid, GetCurrentTransactionId());
 
-		dlist_init(&src->mappings);
-		src->num_mappings = 0;
+		dclist_init(&src->mappings);
 		src->off = 0;
 		memcpy(src->path, path, sizeof(path));
 		src->vfd = PathNameOpenFile(path,
@@ -1017,8 +1015,7 @@ logical_rewrite_log_mapping(RewriteState state, TransactionId xid,
 	pmap = MemoryContextAlloc(state->rs_cxt,
 							  sizeof(RewriteMappingDataEntry));
 	memcpy(&pmap->map, map, sizeof(LogicalRewriteMappingData));
-	dlist_push_tail(&src->mappings, &pmap->node);
-	src->num_mappings++;
+	dclist_push_tail(&src->mappings, &pmap->node);
 	state->rs_num_rewrite_mappings++;
 
 	/*
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 5eff87665b..09c9409c31 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -319,8 +319,7 @@ typedef struct mXactCacheEnt
 } mXactCacheEnt;
 
 #define MAX_CACHE_ENTRIES	256
-static dlist_head MXactCache = DLIST_STATIC_INIT(MXactCache);
-static int	MXactCacheMembers = 0;
+static dclist_head MXactCache = DCLIST_STATIC_INIT(MXactCache);
 static MemoryContext MXactContext = NULL;
 
 #ifdef MULTIXACT_DEBUG
@@ -1504,9 +1503,9 @@ mXactCacheGetBySet(int nmembers, MultiXactMember *members)
 	/* sort the array so comparison is easy */
 	qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
 
-	dlist_foreach(iter, &MXactCache)
+	dclist_foreach(iter, &MXactCache)
 	{
-		mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
+		mXactCacheEnt *entry = dclist_container(mXactCacheEnt, node, iter.cur);
 
 		if (entry->nmembers != nmembers)
 			continue;
@@ -1518,7 +1517,7 @@ mXactCacheGetBySet(int nmembers, MultiXactMember *members)
 		if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
 		{
 			debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
-			dlist_move_head(&MXactCache, iter.cur);
+			dclist_move_head(&MXactCache, iter.cur);
 			return entry->multi;
 		}
 	}
@@ -1542,9 +1541,9 @@ mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
 
 	debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
 
-	dlist_foreach(iter, &MXactCache)
+	dclist_foreach(iter, &MXactCache)
 	{
-		mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
+		mXactCacheEnt *entry = dclist_container(mXactCacheEnt, node, iter.cur);
 
 		if (entry->multi == multi)
 		{
@@ -1566,7 +1565,7 @@ mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
 			 * This is acceptable only because we exit the iteration
 			 * immediately afterwards.
 			 */
-			dlist_move_head(&MXactCache, iter.cur);
+			dclist_move_head(&MXactCache, iter.cur);
 
 			*members = ptr;
 			return entry->nmembers;
@@ -1610,16 +1609,15 @@ mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
 	/* mXactCacheGetBySet assumes the entries are sorted, so sort them */
 	qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
 
-	dlist_push_head(&MXactCache, &entry->node);
-	if (MXactCacheMembers++ >= MAX_CACHE_ENTRIES)
+	dclist_push_head(&MXactCache, &entry->node);
+	if (dclist_count(&MXactCache) > MAX_CACHE_ENTRIES)
 	{
 		dlist_node *node;
 
-		node = dlist_tail_node(&MXactCache);
-		dlist_delete(node);
-		MXactCacheMembers--;
+		node = dclist_tail_node(&MXactCache);
+		dclist_delete_from(&MXactCache, node);
 
-		entry = dlist_container(mXactCacheEnt, node, node);
+		entry = dclist_container(mXactCacheEnt, node, node);
 		debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
 					entry->multi);
 
@@ -1699,8 +1697,7 @@ AtEOXact_MultiXact(void)
 	 * a child of TopTransactionContext, we needn't delete it explicitly.
 	 */
 	MXactContext = NULL;
-	dlist_init(&MXactCache);
-	MXactCacheMembers = 0;
+	dclist_init(&MXactCache);
 }
 
 /*
@@ -1766,8 +1763,7 @@ PostPrepare_MultiXact(TransactionId xid)
 	 * Discard the local MultiXactId cache like in AtEOXact_MultiXact.
 	 */
 	MXactContext = NULL;
-	dlist_init(&MXactCache);
-	MXactCacheMembers = 0;
+	dclist_init(&MXactCache);
 }
 
 /*
diff --git a/src/backend/lib/ilist.c b/src/backend/lib/ilist.c
index 29ef216212..e8ea981176 100644
--- a/src/backend/lib/ilist.c
+++ b/src/backend/lib/ilist.c
@@ -52,6 +52,23 @@ slist_delete(slist_head *head, slist_node *node)
 }
 
 #ifdef ILIST_DEBUG
+/*
+ * dlist_member_check
+ *		Validate that 'node' is a member of 'head'
+ */
+void
+dlist_member_check(dlist_head *head, dlist_node *node)
+{
+	dlist_iter	iter;
+
+	dlist_foreach(iter, head)
+	{
+		if (iter.cur == node)
+			return;
+	}
+	elog(ERROR, "double linked list member check failure");
+}
+
 /*
  * Verify integrity of a doubly linked list
  */
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 20c9cd139a..22a15a482a 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -349,8 +349,6 @@ ReorderBufferAllocate(void)
 	buffer->by_txn_last_xid = InvalidTransactionId;
 	buffer->by_txn_last_txn = NULL;
 
-	buffer->catchange_ntxns = 0;
-
 	buffer->outbuf = NULL;
 	buffer->outbufsize = 0;
 	buffer->size = 0;
@@ -368,7 +366,7 @@ ReorderBufferAllocate(void)
 
 	dlist_init(&buffer->toplevel_by_lsn);
 	dlist_init(&buffer->txns_by_base_snapshot_lsn);
-	dlist_init(&buffer->catchange_txns);
+	dclist_init(&buffer->catchange_txns);
 
 	/*
 	 * Ensure there's no stale data from prior uses of this slot, in case some
@@ -1553,12 +1551,7 @@ ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	 */
 	dlist_delete(&txn->node);
 	if (rbtxn_has_catalog_changes(txn))
-	{
-		dlist_delete(&txn->catchange_node);
-		rb->catchange_ntxns--;
-
-		Assert(rb->catchange_ntxns >= 0);
-	}
+		dclist_delete_from(&rb->catchange_txns, &txn->catchange_node);
 
 	/* now remove reference from buffer */
 	hash_search(rb->by_txn,
@@ -3309,8 +3302,7 @@ ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid,
 	if (!rbtxn_has_catalog_changes(txn))
 	{
 		txn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
-		dlist_push_tail(&rb->catchange_txns, &txn->catchange_node);
-		rb->catchange_ntxns++;
+		dclist_push_tail(&rb->catchange_txns, &txn->catchange_node);
 	}
 
 	/*
@@ -3323,8 +3315,7 @@ ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid,
 	if (toptxn != NULL && !rbtxn_has_catalog_changes(toptxn))
 	{
 		toptxn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
-		dlist_push_tail(&rb->catchange_txns, &toptxn->catchange_node);
-		rb->catchange_ntxns++;
+		dclist_push_tail(&rb->catchange_txns, &toptxn->catchange_node);
 	}
 }
 
@@ -3342,19 +3333,17 @@ ReorderBufferGetCatalogChangesXacts(ReorderBuffer *rb)
 	size_t		xcnt = 0;
 
 	/* Quick return if the list is empty */
-	if (rb->catchange_ntxns == 0)
-	{
-		Assert(dlist_is_empty(&rb->catchange_txns));
+	if (dclist_count(&rb->catchange_txns) == 0)
 		return NULL;
-	}
 
 	/* Initialize XID array */
-	xids = (TransactionId *) palloc(sizeof(TransactionId) * rb->catchange_ntxns);
-	dlist_foreach(iter, &rb->catchange_txns)
+	xids = (TransactionId *) palloc(sizeof(TransactionId) *
+									dclist_count(&rb->catchange_txns));
+	dclist_foreach(iter, &rb->catchange_txns)
 	{
-		ReorderBufferTXN *txn = dlist_container(ReorderBufferTXN,
-												catchange_node,
-												iter.cur);
+		ReorderBufferTXN *txn = dclist_container(ReorderBufferTXN,
+												 catchange_node,
+												 iter.cur);
 
 		Assert(rbtxn_has_catalog_changes(txn));
 
@@ -3363,7 +3352,7 @@ ReorderBufferGetCatalogChangesXacts(ReorderBuffer *rb)
 
 	qsort(xids, xcnt, sizeof(TransactionId), xidComparator);
 
-	Assert(xcnt == rb->catchange_ntxns);
+	Assert(xcnt == dclist_count(&rb->catchange_txns));
 	return xids;
 }
 
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index f892d19bfb..5006a5c464 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1688,7 +1688,7 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
 
 	/* Get the catalog modifying transactions that are yet not committed */
 	catchange_xip = ReorderBufferGetCatalogChangesXacts(builder->reorder);
-	catchange_xcnt = builder->reorder->catchange_ntxns;
+	catchange_xcnt = dclist_count(&builder->reorder->catchange_txns);
 
 	needed_length = sizeof(SnapBuildOnDisk) +
 		sizeof(TransactionId) * (builder->committed.xcnt + catchange_xcnt);
diff --git a/src/backend/utils/activity/pgstat_xact.c b/src/backend/utils/activity/pgstat_xact.c
index d6f660edf7..5a3aca4aef 100644
--- a/src/backend/utils/activity/pgstat_xact.c
+++ b/src/backend/utils/activity/pgstat_xact.c
@@ -70,16 +70,13 @@ AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
 	dlist_mutable_iter iter;
 	int			not_freed_count = 0;
 
-	if (xact_state->pending_drops_count == 0)
-	{
-		Assert(dlist_is_empty(&xact_state->pending_drops));
+	if (dclist_count(&xact_state->pending_drops) == 0)
 		return;
-	}
 
-	dlist_foreach_modify(iter, &xact_state->pending_drops)
+	dclist_foreach_modify(iter, &xact_state->pending_drops)
 	{
 		PgStat_PendingDroppedStatsItem *pending =
-		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+		dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
 		xl_xact_stats_item *it = &pending->item;
 
 		if (isCommit && !pending->is_create)
@@ -101,8 +98,7 @@ AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
 				not_freed_count++;
 		}
 
-		dlist_delete(&pending->node);
-		xact_state->pending_drops_count--;
+		dclist_delete_from(&xact_state->pending_drops, &pending->node);
 		pfree(pending);
 	}
 
@@ -144,19 +140,18 @@ AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
 	dlist_mutable_iter iter;
 	int			not_freed_count = 0;
 
-	if (xact_state->pending_drops_count == 0)
+	if (dclist_count(&xact_state->pending_drops) == 0)
 		return;
 
 	parent_xact_state = pgstat_get_xact_stack_level(nestDepth - 1);
 
-	dlist_foreach_modify(iter, &xact_state->pending_drops)
+	dclist_foreach_modify(iter, &xact_state->pending_drops)
 	{
 		PgStat_PendingDroppedStatsItem *pending =
-		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+		dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
 		xl_xact_stats_item *it = &pending->item;
 
-		dlist_delete(&pending->node);
-		xact_state->pending_drops_count--;
+		dclist_delete_from(&xact_state->pending_drops, &pending->node);
 
 		if (!isCommit && pending->is_create)
 		{
@@ -175,8 +170,7 @@ AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
 			 * remove the stats object, the surrounding transaction might
 			 * still abort. Pass it on to the parent.
 			 */
-			dlist_push_tail(&parent_xact_state->pending_drops, &pending->node);
-			parent_xact_state->pending_drops_count++;
+			dclist_push_tail(&parent_xact_state->pending_drops, &pending->node);
 		}
 		else
 		{
@@ -184,7 +178,7 @@ AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
 		}
 	}
 
-	Assert(xact_state->pending_drops_count == 0);
+	Assert(dclist_count(&xact_state->pending_drops) == 0);
 	if (not_freed_count > 0)
 		pgstat_request_entry_refs_gc();
 }
@@ -250,8 +244,7 @@ pgstat_get_xact_stack_level(int nest_level)
 		xact_state = (PgStat_SubXactStatus *)
 			MemoryContextAlloc(TopTransactionContext,
 							   sizeof(PgStat_SubXactStatus));
-		dlist_init(&xact_state->pending_drops);
-		xact_state->pending_drops_count = 0;
+		dclist_init(&xact_state->pending_drops);
 		xact_state->nest_level = nest_level;
 		xact_state->prev = pgStatXactStack;
 		xact_state->first = NULL;
@@ -291,20 +284,20 @@ pgstat_get_transactional_drops(bool isCommit, xl_xact_stats_item **items)
 	Assert(!isCommit || xact_state->nest_level == 1);
 	Assert(!isCommit || xact_state->prev == NULL);
 
-	*items = palloc(xact_state->pending_drops_count
+	*items = palloc(dclist_count(&xact_state->pending_drops)
 					* sizeof(xl_xact_stats_item));
 
-	dlist_foreach(iter, &xact_state->pending_drops)
+	dclist_foreach(iter, &xact_state->pending_drops)
 	{
 		PgStat_PendingDroppedStatsItem *pending =
-		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+		dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
 
 		if (isCommit && pending->is_create)
 			continue;
 		if (!isCommit && !pending->is_create)
 			continue;
 
-		Assert(nitems < xact_state->pending_drops_count);
+		Assert(nitems < dclist_count(&xact_state->pending_drops));
 		(*items)[nitems++] = pending->item;
 	}
 
@@ -351,8 +344,7 @@ create_drop_transactional_internal(PgStat_Kind kind, Oid dboid, Oid objoid, bool
 	drop->item.dboid = dboid;
 	drop->item.objoid = objoid;
 
-	dlist_push_tail(&xact_state->pending_drops, &drop->node);
-	xact_state->pending_drops_count++;
+	dclist_push_tail(&xact_state->pending_drops, &drop->node);
 }
 
 /*
diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index 1d503e7e01..61c2eecaca 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -176,8 +176,7 @@ typedef struct RI_CompareHashEntry
 static HTAB *ri_constraint_cache = NULL;
 static HTAB *ri_query_cache = NULL;
 static HTAB *ri_compare_cache = NULL;
-static dlist_head ri_constraint_cache_valid_list;
-static int	ri_constraint_cache_valid_count = 0;
+static dclist_head ri_constraint_cache_valid_list;
 
 
 /*
@@ -2172,10 +2171,9 @@ ri_LoadConstraintInfo(Oid constraintOid)
 
 	/*
 	 * For efficient processing of invalidation messages below, we keep a
-	 * doubly-linked list, and a count, of all currently valid entries.
+	 * doubly-linked count list of all currently valid entries.
 	 */
-	dlist_push_tail(&ri_constraint_cache_valid_list, &riinfo->valid_link);
-	ri_constraint_cache_valid_count++;
+	dclist_push_tail(&ri_constraint_cache_valid_list, &riinfo->valid_link);
 
 	riinfo->valid = true;
 
@@ -2233,13 +2231,13 @@ InvalidateConstraintCacheCallBack(Datum arg, int cacheid, uint32 hashvalue)
 	 * O(N^2) behavior in situations where a session touches many foreign keys
 	 * and also does many ALTER TABLEs, such as a restore from pg_dump.
 	 */
-	if (ri_constraint_cache_valid_count > 1000)
+	if (dclist_count(&ri_constraint_cache_valid_list) > 1000)
 		hashvalue = 0;			/* pretend it's a cache reset */
 
-	dlist_foreach_modify(iter, &ri_constraint_cache_valid_list)
+	dclist_foreach_modify(iter, &ri_constraint_cache_valid_list)
 	{
-		RI_ConstraintInfo *riinfo = dlist_container(RI_ConstraintInfo,
-													valid_link, iter.cur);
+		RI_ConstraintInfo *riinfo = dclist_container(RI_ConstraintInfo,
+													 valid_link, iter.cur);
 
 		/*
 		 * We must invalidate not only entries directly matching the given
@@ -2252,8 +2250,7 @@ InvalidateConstraintCacheCallBack(Datum arg, int cacheid, uint32 hashvalue)
 		{
 			riinfo->valid = false;
 			/* Remove invalidated entries from the list, too */
-			dlist_delete(iter.cur);
-			ri_constraint_cache_valid_count--;
+			dclist_delete_from(&ri_constraint_cache_valid_list, iter.cur);
 		}
 	}
 }
diff --git a/src/include/lib/ilist.h b/src/include/lib/ilist.h
index 7ab0888f4f..4ac0afe5e7 100644
--- a/src/include/lib/ilist.h
+++ b/src/include/lib/ilist.h
@@ -10,20 +10,36 @@
  * the link fields in the remainder would be wasted space.  But usually,
  * it saves space to not have separately-allocated list nodes.)
  *
+ * The doubly-linked list comes in 2 forms.  dlist_head defines a head of a
+ * doubly-linked list of dlist_nodes.  Whereas dclist_head defines the head of
+ * a doubly-linked list of dlist_nodes with an additional 'count' field to
+ * keep track of how many items are contained within the given list.  For
+ * simplicity dlist_head and dclist_head share the same node and iterator
+ * types.  The functions to manipulate a dlist_head always have a name
+ * starting with "dlist", whereas functions to manipulate a dclist_head have a
+ * name starting with "dclist".  dclist_head comes with an additional function
+ * (dclist_count) to return the number of entries in the list.  dclists are
+ * able to store a maximum of PG_UINT32_MAX elements.  It is up to the caller
+ * to ensure no more than this many items are added to a dclist.
+ *
  * None of the functions here allocate any memory; they just manipulate
- * externally managed memory.  The APIs for singly and doubly linked lists
- * are identical as far as capabilities of both allow.
+ * externally managed memory.  With the exception doubly-linked count lists
+ * providing the ability to obtain the number of items in the list, the APIs
+ * for singly and both doubly linked lists are identical as far as
+ * capabilities of both allow.
  *
  * Each list has a list header, which exists even when the list is empty.
  * An empty singly-linked list has a NULL pointer in its header.
- * There are two kinds of empty doubly linked lists: those that have been
- * initialized to NULL, and those that have been initialized to circularity.
+ *
+ * For both doubly-linked list types, there are two valid ways to represent an
+ * empty list.  The head's 'next' pointer can either be NULL or the head's
+ * 'next' and 'prev' links can both point back to the list head (circular).
  * (If a dlist is modified and then all its elements are deleted, it will be
- * in the circular state.)	We prefer circular dlists because there are some
+ * in the circular state.).  We prefer circular dlists because there are some
  * operations that can be done without branches (and thus faster) on lists
  * that use circular representation.  However, it is often convenient to
  * initialize list headers to zeroes rather than setting them up with an
- * explicit initialization function, so we also allow the other case.
+ * explicit initialization function, so we also allow the NULL initalization.
  *
  * EXAMPLES
  *
@@ -146,15 +162,17 @@ typedef struct dlist_head
 
 
 /*
- * Doubly linked list iterator.
+ * Doubly linked list iterator type for dlist_head and and dclist_head types.
+ *
+ * Used as state in dlist_foreach() and dlist_reverse_foreach() (and the
+ * dclist variant thereof).
  *
- * Used as state in dlist_foreach() and dlist_reverse_foreach(). To get the
- * current element of the iteration use the 'cur' member.
+ * To get the current element of the iteration use the 'cur' member.
  *
  * Iterations using this are *not* allowed to change the list while iterating!
  *
  * NB: We use an extra "end" field here to avoid multiple evaluations of
- * arguments in the dlist_foreach() macro.
+ * arguments in the dlist_foreach() and dclist_foreach() macros.
  */
 typedef struct dlist_iter
 {
@@ -163,10 +181,12 @@ typedef struct dlist_iter
 } dlist_iter;
 
 /*
- * Doubly linked list iterator allowing some modifications while iterating.
+ * Doubly linked list iterator for both dlist_head and dclist_head types.
+ * This iterator type allows some modifications while iterating.
  *
- * Used as state in dlist_foreach_modify(). To get the current element of the
- * iteration use the 'cur' member.
+ * Used as state in dlist_foreach_modify() and dclist_foreach_modify().
+ *
+ * To get the current element of the iteration use the 'cur' member.
  *
  * Iterations using this are only allowed to change the list at the current
  * point of iteration. It is fine to delete the current node, but it is *not*
@@ -182,6 +202,19 @@ typedef struct dlist_mutable_iter
 	dlist_node *end;			/* last node we'll iterate to */
 } dlist_mutable_iter;
 
+/*
+ * Head of a doubly linked list with a count of the number of items
+ *
+ * This internally makes use of a dlist to implement the actual list and
+ * wrapper functions are used to maintain the count when items are added and
+ * removed from the list.
+ */
+typedef struct dclist_head
+{
+	dlist_head	dlist;			/* the actual list header */
+	uint32		count;			/* the number of items in the list */
+} dclist_head;
+
 /*
  * Node of a singly linked list.
  *
@@ -246,6 +279,7 @@ typedef struct slist_mutable_iter
 
 /* Static initializers */
 #define DLIST_STATIC_INIT(name) {{&(name).head, &(name).head}}
+#define DCLIST_STATIC_INIT(name) {{{&(name).dlist.head, &(name).dlist.head}}, 0}
 #define SLIST_STATIC_INIT(name) {{NULL}}
 
 
@@ -255,6 +289,7 @@ typedef struct slist_mutable_iter
 extern void slist_delete(slist_head *head, slist_node *node);
 
 #ifdef ILIST_DEBUG
+extern void dlist_member_check(dlist_head *head, dlist_node *node);
 extern void dlist_check(dlist_head *head);
 extern void slist_check(slist_head *head);
 #else
@@ -264,6 +299,7 @@ extern void slist_check(slist_head *head);
  * in which functions the only point of passing the list head pointer is to be
  * able to run these checks.
  */
+#define dlist_member_check(head, node) ((void) (head))
 #define dlist_check(head)	((void) (head))
 #define slist_check(head)	((void) (head))
 #endif							/* ILIST_DEBUG */
@@ -361,6 +397,17 @@ dlist_delete(dlist_node *node)
 	node->next->prev = node->prev;
 }
 
+/*
+ * Same as dlist_delete, but performs checks in ILIST_DEBUG builds to ensure
+ * that 'node' belongs to 'head'.
+ */
+static inline void
+dlist_delete_from(dlist_head *head, dlist_node *node)
+{
+	dlist_member_check(head, node);
+	dlist_delete(node);
+}
+
 /*
  * Remove and return the first node from a list (there must be one).
  */
@@ -562,6 +609,309 @@ dlist_tail_node(dlist_head *head)
 		 (iter).cur != (iter).end;											\
 		 (iter).cur = (iter).cur->prev)
 
+/* doubly-linked count list implementation */
+
+/*
+ * dclist_init
+ *		Initialize a doubly linked count list.
+ *
+ * Previous state will be thrown away without any cleanup.
+ */
+static inline void
+dclist_init(dclist_head *head)
+{
+	dlist_init(&head->dlist);
+	head->count = 0;
+}
+
+/*
+ * dclist_is_empty
+ *		Returns true if the list is empty, otherwise false.
+ */
+static inline bool
+dclist_is_empty(dclist_head *head)
+{
+	Assert(dlist_is_empty(&head->dlist) == (head->count == 0));
+	return (head->count == 0);
+}
+
+/*
+ * dclist_push_head
+ *		Insert a node at the beginning of the list.
+ */
+static inline void
+dclist_push_head(dclist_head *head, dlist_node *node)
+{
+	if (head->dlist.head.next == NULL)	/* convert NULL header to circular */
+		dclist_init(head);
+
+	dlist_push_head(&head->dlist, node);
+	head->count++;
+
+	Assert(head->count > 0);	/* count overflow check */
+}
+
+/*
+ * dclist_push_tail
+ *		Insert a node at the end of the list.
+ */
+static inline void
+dclist_push_tail(dclist_head *head, dlist_node *node)
+{
+	if (head->dlist.head.next == NULL)	/* convert NULL header to circular */
+		dclist_init(head);
+
+	dlist_push_tail(&head->dlist, node);
+	head->count++;
+
+	Assert(head->count > 0);	/* count overflow check */
+}
+
+/*
+ * dclist_insert_after
+ *		Insert a node after another *in the same list*
+ *
+ * Caution: 'after' must be a member of 'head'.
+ */
+static inline void
+dclist_insert_after(dclist_head *head, dlist_node *after, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, after);
+	Assert(head->count > 0);	/* must be at least 1 already */
+
+	dlist_insert_after(after, node);
+	head->count++;
+
+	Assert(head->count > 0);	/* count overflow check */
+}
+
+/*
+ * dclist_insert_before
+ *		Insert a node before another *in the same list*
+ *
+ * Caution: 'before' must be a member of 'head'.
+ */
+static inline void
+dclist_insert_before(dclist_head *head, dlist_node *before, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, before);
+	Assert(head->count > 0);	/* must be at least 1 already */
+
+	dlist_insert_before(before, node);
+	head->count++;
+
+	Assert(head->count > 0);	/* count overflow check */
+}
+
+/*
+ * dclist_delete_from
+ *		Deletes 'node' from 'head'.
+ *
+ * Caution: 'node' must be a member of 'head'.
+ */
+static inline void
+dclist_delete_from(dclist_head *head, dlist_node *node)
+{
+	Assert(head->count > 0);
+
+	dlist_delete_from(&head->dlist, node);
+	head->count--;
+}
+
+/*
+ * dclist_pop_head_node
+ *		Remove and return the first node from a list (there must be one).
+ */
+static inline dlist_node *
+dclist_pop_head_node(dclist_head *head)
+{
+	dlist_node *node;
+
+	Assert(head->count > 0);
+
+	node = dlist_pop_head_node(&head->dlist);
+	head->count--;
+	return node;
+}
+
+/*
+ * dclist_move_head
+ *		Move 'node' from its current position in the list to the head position
+ *		in 'head'.
+ *
+ * Caution: 'node' must be a member of 'head'.
+ */
+static inline void
+dclist_move_head(dclist_head *head, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, node);
+	Assert(head->count > 0);
+
+	dlist_move_head(&head->dlist, node);
+}
+
+/*
+ * dclist_move_tail
+ *		Move 'node' from its current position in the list to the tail position
+ *		in 'head'.
+ *
+ * Caution: 'node' must be a member of 'head'.
+ */
+static inline void
+dclist_move_tail(dclist_head *head, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, node);
+	Assert(head->count > 0);
+
+	dlist_move_tail(&head->dlist, node);
+}
+
+/*
+ * dclist_has_next
+ *		Check whether 'node' has a following node.
+ *
+ * Caution: 'node' must be a member of 'head'.
+ */
+static inline bool
+dclist_has_next(dclist_head *head, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, node);
+	Assert(head->count > 0);
+
+	return dlist_has_next(&head->dlist, node);
+}
+
+/*
+ * dclist_has_prev
+ *		Check whether 'node' has a preceding node.
+ *
+ * Caution: 'node' must be a member of 'head'.
+ */
+static inline bool
+dclist_has_prev(dclist_head *head, dlist_node *node)
+{
+	dlist_member_check(&head->dlist, node);
+	Assert(head->count > 0);
+
+	return dlist_has_prev(&head->dlist, node);
+}
+
+/*
+ * dclist_next_node
+ *		Return the next node in the list (there must be one).
+ */
+static inline dlist_node *
+dclist_next_node(dclist_head *head, dlist_node *node)
+{
+	Assert(head->count > 0);
+
+	return dlist_next_node(&head->dlist, node);
+}
+
+/*
+ * dclist_prev_node
+ *		Return the prev node in the list (there must be one).
+ */
+static inline dlist_node *
+dclist_prev_node(dclist_head *head, dlist_node *node)
+{
+	Assert(head->count > 0);
+
+	return dlist_prev_node(&head->dlist, node);
+}
+
+/* internal support function to get address of head element's struct */
+static inline void *
+dclist_head_element_off(dclist_head *head, size_t off)
+{
+	Assert(!dclist_is_empty(head));
+
+	return (char *) head->dlist.head.next - off;
+}
+
+/*
+ * dclist_head_node
+ *		Return the first node in the list (there must be one).
+ */
+static inline dlist_node *
+dclist_head_node(dclist_head *head)
+{
+	Assert(head->count > 0);
+
+	return (dlist_node *) dlist_head_element_off(&head->dlist, 0);
+}
+
+/* internal support function to get address of tail element's struct */
+static inline void *
+dclist_tail_element_off(dclist_head *head, size_t off)
+{
+	Assert(!dclist_is_empty(head));
+
+	return (char *) head->dlist.head.prev - off;
+}
+
+/*
+ * Return the last node in the list (there must be one).
+ */
+static inline dlist_node *
+dclist_tail_node(dclist_head *head)
+{
+	Assert(head->count > 0);
+
+	return (dlist_node *) dlist_tail_element_off(&head->dlist, 0);
+}
+
+/*
+ * dclist_count
+ *		Returns the stored number of entries in 'head'
+ */
+static inline uint32
+dclist_count(dclist_head *head)
+{
+	Assert(dlist_is_empty(&head->dlist) == (head->count == 0));
+
+	return head->count;
+}
+
+/*
+ * Return the containing struct of 'type' where 'membername' is the dlist_node
+ * pointed at by 'ptr'.
+ *
+ * This is used to convert a dlist_node * back to its containing struct.
+ *
+ * Note: This is effectively just the same as dlist_container, so reuse that.
+ */
+#define dclist_container(type, membername, ptr) \
+		dlist_container(type, membername, ptr)
+
+ /*
+  * Return the address of the first element in the list.
+  *
+  * The list must not be empty.
+  */
+#define dclist_head_element(type, membername, lhead)							\
+	(AssertVariableIsOfTypeMacro(((type *) NULL)->membername, dlist_node),	\
+	 (type *) dclist_head_element_off(lhead, offsetof(type, membername)))
+
+ /*
+  * Return the address of the last element in the list.
+  *
+  * The list must not be empty.
+  */
+#define dclist_tail_element(type, membername, lhead)							\
+	(AssertVariableIsOfTypeMacro(((type *) NULL)->membername, dlist_node),	\
+	 ((type *) dclist_tail_element_off(lhead, offsetof(type, membername))))
+
+
+/* Iterators for dclists */
+#define dclist_foreach(iter, lhead) \
+	dlist_foreach(iter, &((lhead)->dlist))
+
+#define dclist_foreach_modify(iter, lhead) \
+	dlist_foreach_modify(iter, &((lhead)->dlist))
+
+#define dclist_reverse_foreach(iter, lhead) \
+	dlist_reverse_foreach(iter, &((lhead)->dlist))
 
 /* singly linked list implementation */
 
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 02b59a1931..b23d8cc4f9 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -534,8 +534,7 @@ struct ReorderBuffer
 	/*
 	 * Transactions and subtransactions that have modified system catalogs.
 	 */
-	dlist_head	catchange_txns;
-	int			catchange_ntxns;
+	dclist_head catchange_txns;
 
 	/*
 	 * one-entry sized cache for by_txn. Very frequently the same txn gets
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index c869533b28..e2c7b59324 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -162,8 +162,7 @@ typedef struct PgStat_SubXactStatus
 	 * if the transaction commits/aborts. To handle replicas and crashes,
 	 * stats drops are included in commit / abort records.
 	 */
-	dlist_head	pending_drops;
-	int			pending_drops_count;
+	dclist_head pending_drops;
 
 	/*
 	 * Tuple insertion/deletion counts for an open transaction can't be
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 2f02cc8f42..c15f990cbb 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -3194,6 +3194,7 @@ datapagemap_t
 dateKEY
 datetkn
 dce_uuid_t
+dclist_head
 decimal
 deparse_columns
 deparse_context