From 78f16c5cc57c1d8f60f69d583411ab403f6dba36 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sun, 7 Jan 2024 17:03:17 -0500
Subject: [PATCH v2 10/17] Inline heap_freeze_execute_prepared()

In order to merge freeze and prune records, the execution of tuple
freezing and the WAL logging of the changes to the page must be
separated so that the WAL logging can be combined with prune WAL
logging. This commit makes a helper for the tuple freezing and then
inlines the contents of heap_freeze_execute_prepared() where it is
called in heap_page_prune(). The original function,
heap_freeze_execute_prepared() is retained because the "no prune" case
in heap_page_prune() must still be able to emit a freeze record.
---
 src/backend/access/heap/heapam.c    | 61 +++++++++++++++++------------
 src/backend/access/heap/pruneheap.c | 51 ++++++++++++++++++++++--
 src/include/access/heapam.h         |  8 ++++
 3 files changed, 90 insertions(+), 30 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 16e3f2520a4..a3691584c55 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -91,9 +91,6 @@ static void compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
 static TM_Result heap_lock_updated_tuple(Relation rel, HeapTuple tuple,
 										 ItemPointer ctid, TransactionId xid,
 										 LockTupleMode mode);
-static int	heap_log_freeze_plan(HeapTupleFreeze *tuples, int ntuples,
-								 xl_heap_freeze_plan *plans_out,
-								 OffsetNumber *offsets_out);
 static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
 								   uint16 *new_infomask2);
 static TransactionId MultiXactIdGetUpdateXid(TransactionId xmax,
@@ -6713,30 +6710,17 @@ heap_pre_freeze_checks(Buffer buffer,
 }
 
 /*
- * heap_freeze_execute_prepared
- *
- * Executes freezing of one or more heap tuples on a page on behalf of caller.
- * Caller passes an array of tuple plans from heap_prepare_freeze_tuple.
- * Caller must set 'offset' in each plan for us.  Note that we destructively
- * sort caller's tuples array in-place, so caller had better be done with it.
- *
- * WAL-logs the changes so that VACUUM can advance the rel's relfrozenxid
- * later on without any risk of unsafe pg_xact lookups, even following a hard
- * crash (or when querying from a standby).  We represent freezing by setting
- * infomask bits in tuple headers, but this shouldn't be thought of as a hint.
- * See section on buffer access rules in src/backend/storage/buffer/README.
+ * Helper which executes freezing of one or more heap tuples on a page on
+ * behalf of caller. Caller passes an array of tuple plans from
+ * heap_prepare_freeze_tuple. Caller must set 'offset' in each plan for us.
+ * Must be called in a critical section that also marks the buffer dirty and,
+ * if needed, emits WAL.
  */
 void
-heap_freeze_execute_prepared(Relation rel, Buffer buffer,
-							 TransactionId snapshotConflictHorizon,
-							 HeapTupleFreeze *tuples, int ntuples)
+heap_freeze_prepared_tuples(Buffer buffer, HeapTupleFreeze *tuples, int ntuples)
 {
 	Page		page = BufferGetPage(buffer);
 
-	Assert(ntuples > 0);
-
-	START_CRIT_SECTION();
-
 	for (int i = 0; i < ntuples; i++)
 	{
 		HeapTupleFreeze *frz = tuples + i;
@@ -6746,6 +6730,29 @@ heap_freeze_execute_prepared(Relation rel, Buffer buffer,
 		htup = (HeapTupleHeader) PageGetItem(page, itemid);
 		heap_execute_freeze_tuple(htup, frz);
 	}
+}
+
+/*
+ * heap_freeze_execute_prepared
+ *
+ * Execute freezing of prepared tuples and WAL-logs the changes so that VACUUM
+ * can advance the rel's relfrozenxid later on without any risk of unsafe
+ * pg_xact lookups, even following a hard crash (or when querying from a
+ * standby).  We represent freezing by setting infomask bits in tuple headers,
+ * but this shouldn't be thought of as a hint. See section on buffer access
+ * rules in src/backend/storage/buffer/README. Must be called from within a
+ * critical section.
+ */
+void
+heap_freeze_execute_prepared(Relation rel, Buffer buffer,
+							 TransactionId snapshotConflictHorizon,
+							 HeapTupleFreeze *tuples, int ntuples)
+{
+	Page		page = BufferGetPage(buffer);
+
+	Assert(ntuples > 0);
+
+	heap_freeze_prepared_tuples(buffer, tuples, ntuples);
 
 	MarkBufferDirty(buffer);
 
@@ -6758,7 +6765,11 @@ heap_freeze_execute_prepared(Relation rel, Buffer buffer,
 		xl_heap_freeze_page xlrec;
 		XLogRecPtr	recptr;
 
-		/* Prepare deduplicated representation for use in WAL record */
+		/*
+		 * Prepare deduplicated representation for use in WAL record
+		 * Destructively sorts tuples array in-place, so caller had better be
+		 * done with it.
+		 */
 		nplans = heap_log_freeze_plan(tuples, ntuples, plans, offsets);
 
 		xlrec.snapshotConflictHorizon = snapshotConflictHorizon;
@@ -6783,8 +6794,6 @@ heap_freeze_execute_prepared(Relation rel, Buffer buffer,
 
 		PageSetLSN(page, recptr);
 	}
-
-	END_CRIT_SECTION();
 }
 
 /*
@@ -6874,7 +6883,7 @@ heap_log_freeze_new_plan(xl_heap_freeze_plan *plan, HeapTupleFreeze *frz)
  * (actually there is one array per freeze plan, but that's not of immediate
  * concern to our caller).
  */
-static int
+int
 heap_log_freeze_plan(HeapTupleFreeze *tuples, int ntuples,
 					 xl_heap_freeze_plan *plans_out,
 					 OffsetNumber *offsets_out)
diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
index bac461940de..d8b7eea5c21 100644
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -613,10 +613,53 @@ heap_page_prune_and_freeze(Relation relation, Buffer buffer,
 
 	if (do_freeze)
 	{
-		/* Execute all freeze plans for page as a single atomic action */
-		heap_freeze_execute_prepared(relation, buffer,
-									 frz_conflict_horizon,
-									 frozen, presult->nfrozen);
+		START_CRIT_SECTION();
+
+		Assert(presult->nfrozen > 0);
+
+		heap_freeze_prepared_tuples(buffer, frozen, presult->nfrozen);
+
+		MarkBufferDirty(buffer);
+
+		/* Now WAL-log freezing if necessary */
+		if (RelationNeedsWAL(relation))
+		{
+			xl_heap_freeze_plan plans[MaxHeapTuplesPerPage];
+			OffsetNumber offsets[MaxHeapTuplesPerPage];
+			int			nplans;
+			xl_heap_freeze_page xlrec;
+			XLogRecPtr	recptr;
+
+			/*
+			 * Prepare deduplicated representation for use in WAL record
+			 * Destructively sorts tuples array in-place.
+			 */
+			nplans = heap_log_freeze_plan(frozen, presult->nfrozen, plans, offsets);
+
+			xlrec.snapshotConflictHorizon = frz_conflict_horizon;
+			xlrec.isCatalogRel = RelationIsAccessibleInLogicalDecoding(relation);
+			xlrec.nplans = nplans;
+
+			XLogBeginInsert();
+			XLogRegisterData((char *) &xlrec, SizeOfHeapFreezePage);
+
+			/*
+			 * The freeze plan array and offset array are not actually in the
+			 * buffer, but pretend that they are.  When XLogInsert stores the
+			 * whole buffer, the arrays need not be stored too.
+			 */
+			XLogRegisterBuffer(0, buffer, REGBUF_STANDARD);
+			XLogRegisterBufData(0, (char *) plans,
+								nplans * sizeof(xl_heap_freeze_plan));
+			XLogRegisterBufData(0, (char *) offsets,
+								presult->nfrozen * sizeof(OffsetNumber));
+
+			recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE_PAGE);
+
+			PageSetLSN(page, recptr);
+		}
+
+		END_CRIT_SECTION();
 	}
 	else if (!pagefrz || !presult->all_frozen || presult->nfrozen > 0)
 	{
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index d14f36d9ce7..41ebbb9f931 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -14,6 +14,7 @@
 #ifndef HEAPAM_H
 #define HEAPAM_H
 
+#include "access/heapam_xlog.h"
 #include "access/relation.h"	/* for backward compatibility */
 #include "access/relscan.h"
 #include "access/sdir.h"
@@ -321,9 +322,16 @@ extern void heap_pre_freeze_checks(Buffer buffer,
 extern void heap_freeze_execute_prepared(Relation rel, Buffer buffer,
 										 TransactionId snapshotConflictHorizon,
 										 HeapTupleFreeze *tuples, int ntuples);
+
+extern void heap_freeze_prepared_tuples(Buffer buffer,
+										HeapTupleFreeze *tuples, int ntuples);
 extern bool heap_freeze_tuple(HeapTupleHeader tuple,
 							  TransactionId relfrozenxid, TransactionId relminmxid,
 							  TransactionId FreezeLimit, TransactionId MultiXactCutoff);
+
+extern int	heap_log_freeze_plan(HeapTupleFreeze *tuples, int ntuples,
+								 xl_heap_freeze_plan *plans_out,
+								 OffsetNumber *offsets_out);
 extern bool heap_tuple_should_freeze(HeapTupleHeader tuple,
 									 const struct VacuumCutoffs *cutoffs,
 									 TransactionId *NoFreezePageRelfrozenXid,
-- 
2.40.1

