From 622620a7875ae8c1626e9cd118156e0c734d44ed Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Sun, 17 Mar 2024 22:52:28 +0200
Subject: [PATCH v3heikki 1/4] Inline heap_frz_conflict_horizon() to the
 caller.

FIXME: This frz_conflict_horizon business looks fishy to me. We have:
- local frz_conflict_horizon variable,
- presult->frz_conflict_horizon, and
- prstate.snapshotConflictHorizon

should we really have all three, and what are the differences?
---
 src/backend/access/heap/pruneheap.c  | 17 ++++++++++++++---
 src/backend/access/heap/vacuumlazy.c | 27 ---------------------------
 src/include/access/heapam.h          |  2 --
 3 files changed, 14 insertions(+), 32 deletions(-)

diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
index d3643b1ecc6..f4f5468e144 100644
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -21,6 +21,7 @@
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "access/xloginsert.h"
+#include "commands/vacuum.h"
 #include "executor/instrument.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -275,7 +276,6 @@ heap_page_prune_and_freeze(Relation relation, Buffer buffer,
 	bool		hint_bit_fpi;
 	bool		prune_fpi = false;
 	int64		fpi_before = pgWalUsage.wal_fpi;
-	TransactionId frz_conflict_horizon = InvalidTransactionId;
 
 	/*
 	 * One entry for every tuple that we may freeze.
@@ -691,7 +691,18 @@ heap_page_prune_and_freeze(Relation relation, Buffer buffer,
 
 	if (do_freeze)
 	{
-		frz_conflict_horizon = heap_frz_conflict_horizon(presult, pagefrz);
+		/*
+		 * We can use frz_conflict_horizon as our cutoff for conflicts when
+		 * the whole page is eligible to become all-frozen in the VM once
+		 * we're done with it.  Otherwise we generate a conservative cutoff by
+		 * stepping back from OldestXmin.
+		 */
+		if (!(presult->all_visible_except_removable && presult->all_frozen))
+		{
+			/* Avoids false conflicts when hot_standby_feedback in use */
+			presult->frz_conflict_horizon = pagefrz->cutoffs->OldestXmin;
+			TransactionIdRetreat(presult->frz_conflict_horizon);
+		}
 		heap_freeze_prepared_tuples(buffer, frozen, presult->nfrozen);
 	}
 	else if ((!pagefrz || !presult->all_frozen || presult->nfrozen > 0))
@@ -740,7 +751,7 @@ heap_page_prune_and_freeze(Relation relation, Buffer buffer,
 		 */
 		if (do_freeze)
 			xlrec.snapshotConflictHorizon = Max(prstate.snapshotConflictHorizon,
-												frz_conflict_horizon);
+												presult->frz_conflict_horizon);
 		else
 			xlrec.snapshotConflictHorizon = prstate.snapshotConflictHorizon;
 
diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 4b45e8be1ad..8d3723faf3a 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -1373,33 +1373,6 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno,
 	return false;
 }
 
-/*
- * Determine the snapshotConflictHorizon for freezing. Must only be called
- * after pruning and determining if the page is freezable.
- */
-TransactionId
-heap_frz_conflict_horizon(PruneFreezeResult *presult, HeapPageFreeze *pagefrz)
-{
-	TransactionId result;
-
-	/*
-	 * We can use frz_conflict_horizon as our cutoff for conflicts when the
-	 * whole page is eligible to become all-frozen in the VM once we're done
-	 * with it.  Otherwise we generate a conservative cutoff by stepping back
-	 * from OldestXmin.
-	 */
-	if (presult->all_visible_except_removable && presult->all_frozen)
-		result = presult->frz_conflict_horizon;
-	else
-	{
-		/* Avoids false conflicts when hot_standby_feedback in use */
-		result = pagefrz->cutoffs->OldestXmin;
-		TransactionIdRetreat(result);
-	}
-
-	return result;
-}
-
 /*
  *	lazy_scan_prune() -- lazy_scan_heap() pruning and freezing.
  *
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index c36623f53bd..4e17347e625 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -290,8 +290,6 @@ extern TM_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
 
 extern void heap_inplace_update(Relation relation, HeapTuple tuple);
 
-extern TransactionId heap_frz_conflict_horizon(PruneFreezeResult *presult,
-											   HeapPageFreeze *pagefrz);
 extern bool heap_prepare_freeze_tuple(HeapTupleHeader tuple,
 									  HeapPageFreeze *pagefrz,
 									  HeapTupleFreeze *frz, bool *totally_frozen);
-- 
2.39.2