Return data from heap_page_prune via a struct.

Previously, one of the values in the struct was returned as the return
value, and another was returned via an output parameter. In
preparation for returning more stuff, consolidate both values into a
struct returned via an output parameter.

Melanie Plageman, reviewed by Andres Freund and by me.

Discussion: https://postgr.es/m/CAAKRu_br124qsGJieuYA0nGjywEukhK1dKBfRdby_4yY3E9SXA%40mail.gmail.com

Author: robertmhaas

src/backend/access/heap/pruneheap.c

@@ -155,15 +155,13 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
 		 */
 		if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
 		{
-			int			ndeleted,
-						nnewlpdead;
+			PruneResult presult;
 
-			ndeleted = heap_page_prune(relation, buffer, vistest,
-									   &nnewlpdead, NULL);
+			heap_page_prune(relation, buffer, vistest, &presult, NULL);
 
 			/*
 			 * Report the number of tuples reclaimed to pgstats.  This is
-			 * ndeleted minus the number of newly-LP_DEAD-set items.
+			 * presult.ndeleted minus the number of newly-LP_DEAD-set items.
 			 *
 			 * We derive the number of dead tuples like this to avoid totally
 			 * forgetting about items that were set to LP_DEAD, since they
@@ -175,9 +173,9 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
 			 * tracks ndeleted, since it will set the same LP_DEAD items to
 			 * LP_UNUSED separately.
 			 */
-			if (ndeleted > nnewlpdead)
+			if (presult.ndeleted > presult.nnewlpdead)
 				pgstat_update_heap_dead_tuples(relation,
-											   ndeleted - nnewlpdead);
+											   presult.ndeleted - presult.nnewlpdead);
 		}
 
 		/* And release buffer lock */
@@ -204,21 +202,19 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
  * (see heap_prune_satisfies_vacuum and
  * HeapTupleSatisfiesVacuum).
  *
- * Sets *nnewlpdead for caller, indicating the number of items that were
- * newly set LP_DEAD during prune operation.
- *
  * off_loc is the offset location required by the caller to use in error
  * callback.
  *
- * Returns the number of tuples deleted from the page during this call.
+ * presult contains output parameters needed by callers such as the number of
+ * tuples removed and the number of line pointers newly marked LP_DEAD.
+ * heap_page_prune() is responsible for initializing it.
  */
-int
+void
 heap_page_prune(Relation relation, Buffer buffer,
 				GlobalVisState *vistest,
-				int *nnewlpdead,
+				PruneResult *presult,
 				OffsetNumber *off_loc)
 {
-	int			ndeleted = 0;
 	Page		page = BufferGetPage(buffer);
 	BlockNumber blockno = BufferGetBlockNumber(buffer);
 	OffsetNumber offnum,
@@ -244,6 +240,9 @@ heap_page_prune(Relation relation, Buffer buffer,
 	prstate.nredirected = prstate.ndead = prstate.nunused = 0;
 	memset(prstate.marked, 0, sizeof(prstate.marked));
 
+	presult->ndeleted = 0;
+	presult->nnewlpdead = 0;
+
 	maxoff = PageGetMaxOffsetNumber(page);
 	tup.t_tableOid = RelationGetRelid(prstate.rel);
 
@@ -318,7 +317,7 @@ heap_page_prune(Relation relation, Buffer buffer,
 			continue;
 
 		/* Process this item or chain of items */
-		ndeleted += heap_prune_chain(buffer, offnum, &prstate);
+		presult->ndeleted += heap_prune_chain(buffer, offnum, &prstate);
 	}
 
 	/* Clear the offset information once we have processed the given page. */
@@ -419,9 +418,7 @@ heap_page_prune(Relation relation, Buffer buffer,
 	END_CRIT_SECTION();
 
 	/* Record number of newly-set-LP_DEAD items for caller */
-	*nnewlpdead = prstate.ndead;
-
-	return ndeleted;
+	presult->nnewlpdead = prstate.ndead;
 }
 
 

src/backend/access/heap/vacuumlazy.c

@@ -1544,12 +1544,11 @@ lazy_scan_prune(LVRelState *vacrel,
 	ItemId		itemid;
 	HeapTupleData tuple;
 	HTSV_Result res;
-	int			tuples_deleted,
-				tuples_frozen,
+	PruneResult presult;
+	int			tuples_frozen,
 				lpdead_items,
 				live_tuples,
 				recently_dead_tuples;
-	int			nnewlpdead;
 	HeapPageFreeze pagefrz;
 	int64		fpi_before = pgWalUsage.wal_fpi;
 	OffsetNumber deadoffsets[MaxHeapTuplesPerPage];
@@ -1572,7 +1571,6 @@ lazy_scan_prune(LVRelState *vacrel,
 	pagefrz.FreezePageRelminMxid = vacrel->NewRelminMxid;
 	pagefrz.NoFreezePageRelfrozenXid = vacrel->NewRelfrozenXid;
 	pagefrz.NoFreezePageRelminMxid = vacrel->NewRelminMxid;
-	tuples_deleted = 0;
 	tuples_frozen = 0;
 	lpdead_items = 0;
 	live_tuples = 0;
@@ -1581,15 +1579,12 @@ lazy_scan_prune(LVRelState *vacrel,
 	/*
 	 * Prune all HOT-update chains in this page.
 	 *
-	 * We count tuples removed by the pruning step as tuples_deleted.  Its
-	 * final value can be thought of as the number of tuples that have been
-	 * deleted from the table.  It should not be confused with lpdead_items;
+	 * We count the number of tuples removed from the page by the pruning step
+	 * in presult.ndeleted. It should not be confused with lpdead_items;
 	 * lpdead_items's final value can be thought of as the number of tuples
 	 * that were deleted from indexes.
 	 */
-	tuples_deleted = heap_page_prune(rel, buf, vacrel->vistest,
-									 &nnewlpdead,
-									 &vacrel->offnum);
+	heap_page_prune(rel, buf, vacrel->vistest, &presult, &vacrel->offnum);
 
 	/*
 	 * Now scan the page to collect LP_DEAD items and check for tuples
@@ -1929,7 +1924,7 @@ lazy_scan_prune(LVRelState *vacrel,
 	}
 
 	/* Finally, add page-local counts to whole-VACUUM counts */
-	vacrel->tuples_deleted += tuples_deleted;
+	vacrel->tuples_deleted += presult.ndeleted;
 	vacrel->tuples_frozen += tuples_frozen;
 	vacrel->lpdead_items += lpdead_items;
 	vacrel->live_tuples += live_tuples;

src/include/access/heapam.h

@@ -191,6 +191,15 @@ typedef struct HeapPageFreeze
 
 } HeapPageFreeze;
 
+/*
+ * Per-page state returned from pruning
+ */
+typedef struct PruneResult
+{
+	int			ndeleted;		/* Number of tuples deleted from the page */
+	int			nnewlpdead;		/* Number of newly LP_DEAD items */
+} PruneResult;
+
 /* ----------------
  *		function prototypes for heap access method
  *
@@ -284,9 +293,9 @@ extern TransactionId heap_index_delete_tuples(Relation rel,
 /* in heap/pruneheap.c */
 struct GlobalVisState;
 extern void heap_page_prune_opt(Relation relation, Buffer buffer);
-extern int	heap_page_prune(Relation relation, Buffer buffer,
+extern void heap_page_prune(Relation relation, Buffer buffer,
 							struct GlobalVisState *vistest,
-							int *nnewlpdead,
+							PruneResult *presult,
 							OffsetNumber *off_loc);
 extern void heap_page_prune_execute(Buffer buffer,
 									OffsetNumber *redirected, int nredirected,

src/tools/pgindent/typedefs.list

@@ -2151,6 +2151,7 @@ ProjectionPath
 PromptInterruptContext
 ProtocolVersion
 PrsStorage
+PruneResult
 PruneState
 PruneStepResult
 PsqlScanCallbacks