Subject: [PATCH v6 11/14] heapam: Add batch mode mvcc check and use it in page mode

From: Andres Freund <[email-masked]>
Date: Thu, 17 Oct 2024 13:16:36 -0400

There are two reasons for doing so:

1) It is generally faster to perform checks in a batched fashion and making
   sequential scans faster is nice.

2) We would like to stop setting hint bits while pages are being written
   out. The necessary locking becomes visible for page mode scans if done for
   every tuple. With batching the overhead can be amortized to only happen
   once per page.

There are substantial further optimization opportunities along these
lines:

- Right now HeapTupleSatisfiesMVCCBatch() simply uses the single-tuple
  HeapTupleSatisfiesMVCC(), relying on the compiler to inline it. We could
  instead write an explicitly optimized version that avoids repeated xid
  tests.

- Introduce batched version of the serializability test

- Introduce batched version of HeapTupleSatisfiesVacuum

Author:
Reviewed-by:
Discussion: https://postgr.es/m/
Backpatch:
---
 src/include/access/heapam.h                 | 28 +++++++
 src/backend/access/heap/heapam.c            | 91 ++++++++++++++++-----
 src/backend/access/heap/heapam_visibility.c | 47 +++++++++++
 src/tools/pgindent/typedefs.list            |  1 +
 4 files changed, 147 insertions(+), 20 deletions(-)

diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 909db73b7bb..13e4a4096c3 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -410,6 +410,34 @@ extern bool HeapTupleHeaderIsOnlyLocked(HeapTupleHeader tuple);
 extern bool HeapTupleIsSurelyDead(HeapTuple htup,
 								  GlobalVisState *vistest);
 
+/*
+ * FIXME: define to be removed
+ *
+ * Without this I see worse performance. But it's a bit ugly, so I thought
+ * it'd be useful to leave a way in for others to experiment with this.
+ */
+#define BATCHMVCC_FEWER_ARGS
+
+#ifdef BATCHMVCC_FEWER_ARGS
+typedef struct BatchMVCCState
+{
+	HeapTupleData tuples[MaxHeapTuplesPerPage];
+	bool		visible[MaxHeapTuplesPerPage];
+} BatchMVCCState;
+#endif
+
+extern int	HeapTupleSatisfiesMVCCBatch(Snapshot snapshot, Buffer buffer,
+										int ntups,
+#ifdef BATCHMVCC_FEWER_ARGS
+										BatchMVCCState *batchmvcc,
+#else
+										HeapTupleData *tuples,
+										bool *visible,
+#endif
+										OffsetNumber *vistuples_dense);
+
+
+
 /*
  * To avoid leaking too much knowledge about reorderbuffer implementation
  * details this is implemented in reorderbuffer.c not heapam_visibility.c
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 4b0c49f4bb0..ddabd1a3ec3 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -504,42 +504,93 @@ page_collect_tuples(HeapScanDesc scan, Snapshot snapshot,
 					BlockNumber block, int lines,
 					bool all_visible, bool check_serializable)
 {
+	Oid			relid = RelationGetRelid(scan->rs_base.rs_rd);
+#ifdef BATCHMVCC_FEWER_ARGS
+	BatchMVCCState batchmvcc;
+	HeapTupleData *tuples = batchmvcc.tuples;
+	bool	   *visible = batchmvcc.visible;
+#else
+	HeapTupleData tuples[MaxHeapTuplesPerPage];
+	bool		visible[MaxHeapTuplesPerPage];
+#endif
 	int			ntup = 0;
-	OffsetNumber lineoff;
+	int			nvis = 0;
 
-	for (lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++)
+	/* page at a time should have been disabled otherwise */
+	Assert(IsMVCCSnapshot(snapshot));
+
+	/* first find all tuples on the page */
+	for (OffsetNumber lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++)
 	{
 		ItemId		lpp = PageGetItemId(page, lineoff);
-		HeapTupleData loctup;
-		bool		valid;
+		HeapTuple	tup;
 
-		if (!ItemIdIsNormal(lpp))
+		if (unlikely(!ItemIdIsNormal(lpp)))
 			continue;
 
-		loctup.t_data = (HeapTupleHeader) PageGetItem(page, lpp);
-		loctup.t_len = ItemIdGetLength(lpp);
-		loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd);
-		ItemPointerSet(&(loctup.t_self), block, lineoff);
+		/*
+		 * If the page is not all-visible or we need to check serializability,
+		 * maintain enough state to be able to refind the tuple efficiently,
+		 * without again needing to extract it from the page.
+		 */
+		if (!all_visible || check_serializable)
+		{
+			tup = &tuples[ntup];
 
+			tup->t_data = (HeapTupleHeader) PageGetItem(page, lpp);
+			tup->t_len = ItemIdGetLength(lpp);
+			tup->t_tableOid = relid;
+			ItemPointerSet(&(tup->t_self), block, lineoff);
+		}
+
+		/*
+		 * If the page is all visible, these fields won'otherwise wont be
+		 * populated in loop below.
+		 */
 		if (all_visible)
-			valid = true;
-		else
-			valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
-
-		if (check_serializable)
-			HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
-												&loctup, buffer, snapshot);
-
-		if (valid)
 		{
+			if (check_serializable)
+			{
+				visible[ntup] = true;
+			}
 			scan->rs_vistuples[ntup] = lineoff;
-			ntup++;
 		}
+
+		ntup++;
 	}
 
 	Assert(ntup <= MaxHeapTuplesPerPage);
 
-	return ntup;
+	/* unless the page is all visible, test visibility for all tuples one go */
+	if (all_visible)
+		nvis = ntup;
+	else
+		nvis = HeapTupleSatisfiesMVCCBatch(snapshot, buffer,
+										   ntup,
+#ifdef BATCHMVCC_FEWER_ARGS
+										   &batchmvcc,
+#else
+										   tuples, visible,
+#endif
+										   scan->rs_vistuples
+			);
+
+	/*
+	 * So far we don't have batch API for testing serializabilty, so do so
+	 * one-by-one.
+	 */
+	if (check_serializable)
+	{
+		for (int i = 0; i < ntup; i++)
+		{
+			HeapCheckForSerializableConflictOut(visible[i],
+												scan->rs_base.rs_rd,
+												&tuples[i],
+												buffer, snapshot);
+		}
+	}
+
+	return nvis;
 }
 
 /*
diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c
index 762538a2040..5645cfd8a49 100644
--- a/src/backend/access/heap/heapam_visibility.c
+++ b/src/backend/access/heap/heapam_visibility.c
@@ -1584,6 +1584,53 @@ HeapTupleSatisfiesHistoricMVCC(HeapTuple htup, Snapshot snapshot,
 		return true;
 }
 
+/*
+ * Perform HeaptupleSatisfiesMVCC() on each passed in tuple. This is more
+ * efficient than doing HeapTupleSatisfiesMVCC() one-by-one.
+ *
+ * To be checked tuples are passed via BatchMVCCState->tuples. Each tuple's
+ * visibility is set in batchmvcc->visible[]. In addition, ->vistuples_dense
+ * is set to contain the offsets of visible tuples.
+ *
+ * Returns the number of visible tuples.
+ */
+int
+HeapTupleSatisfiesMVCCBatch(Snapshot snapshot, Buffer buffer,
+							int ntups,
+#ifdef BATCHMVCC_FEWER_ARGS
+							BatchMVCCState *batchmvcc,
+#else
+							HeapTupleData *tuples,
+							bool *visible,
+#endif
+							OffsetNumber *vistuples_dense)
+{
+	int			nvis = 0;
+#ifdef BATCHMVCC_FEWER_ARGS
+	HeapTupleData *tuples = batchmvcc->tuples;
+	bool	   *visible = batchmvcc->visible;
+#endif
+
+	Assert(IsMVCCSnapshot(snapshot));
+
+	for (int i = 0; i < ntups; i++)
+	{
+		bool		valid;
+		HeapTuple	tup = &tuples[i];
+
+		valid = HeapTupleSatisfiesMVCC(tup, snapshot, buffer);
+		visible[i] = valid;
+
+		if (likely(valid))
+		{
+			vistuples_dense[nvis] = tup->t_self.ip_posid;
+			nvis++;
+		}
+	}
+
+	return nvis;
+}
+
 /*
  * HeapTupleSatisfiesVisibility
  *		True iff heap tuple satisfies a time qual.
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 9a89e68c59c..9d14239b4c4 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -249,6 +249,7 @@ Barrier
 BaseBackupCmd
 BaseBackupTargetHandle
 BaseBackupTargetType
+BatchMVCCState
 BeginDirectModify_function
 BeginForeignInsert_function
 BeginForeignModify_function
-- 
2.48.1.76.g4e746b1a31.dirty

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