v3-0005-Add-heapgettup-helpers.patch

From 2e63656e75b00b24d286533ae8c8ef291876d4a8 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Wed, 30 Nov 2022 14:18:08 -0500
Subject: [PATCH v3 5/7] Add heapgettup() helpers

Add heapgettup_start_page() and heapgettup_continue_page(), helper
functions for heapgettup().
---
 src/backend/access/heap/heapam.c | 93 +++++++++++++++++++++-----------
 1 file changed, 61 insertions(+), 32 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index a4365beee1..f9b2d5cadb 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -575,6 +575,65 @@ heapgettup_initial_page(HeapScanDesc scan, ScanDirection dir)
 	return scan->rs_nblocks - 1;
 }
 
+static inline Page
+heapgettup_start_page(HeapScanDesc scan, BlockNumber block, ScanDirection dir,
+		int *linesleft, OffsetNumber *lineoff)
+{
+	Page page;
+
+	Assert(scan->rs_inited);
+	Assert(BufferIsValid(scan->rs_cbuf));
+
+	/* Caller is responsible for ensuring buffer is locked if needed */
+	page = BufferGetPage(scan->rs_cbuf);
+
+	TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
+
+	*linesleft = PageGetMaxOffsetNumber((Page) page) - FirstOffsetNumber + 1;
+
+	if (ScanDirectionIsForward(dir))
+		*lineoff = FirstOffsetNumber;
+	else
+		*lineoff = (OffsetNumber) (*linesleft);
+
+	/* lineoff now references the physically previous or next tid */
+	return page;
+}
+
+static inline Page
+heapgettup_continue_page(HeapScanDesc scan, BlockNumber block, ScanDirection
+		dir, int *linesleft, OffsetNumber *lineoff)
+{
+	Page page;
+
+	Assert(scan->rs_inited);
+	Assert(BufferIsValid(scan->rs_cbuf));
+
+	/* Caller is responsible for ensuring buffer is locked if needed */
+	page = BufferGetPage(scan->rs_cbuf);
+
+	TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
+
+	if (ScanDirectionIsForward(dir))
+	{
+		*lineoff = OffsetNumberNext(scan->rs_cindex);
+		*linesleft = PageGetMaxOffsetNumber(page) - (*lineoff) + 1;
+	}
+	else
+	{
+		/*
+		* The previous returned tuple may have been vacuumed since the
+		* previous scan when we use a non-MVCC snapshot, so we must
+		* re-establish the lineoff <= PageGetMaxOffsetNumber(page)
+		* invariant
+		*/
+		*lineoff = Min(PageGetMaxOffsetNumber(page), OffsetNumberPrev(scan->rs_cindex));
+		*linesleft = *lineoff;
+	}
+	/* block and lineoff now reference the physically next tid */
+	return page;
+}
+
 /* ----------------
  *		heapgettup - fetch next heap tuple
  *
@@ -632,45 +691,15 @@ heapgettup(HeapScanDesc scan,
 		}
 
 		heapgetpage((TableScanDesc) scan, block);
-
 		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
-		page = BufferGetPage(scan->rs_cbuf);
-		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
-
-		linesleft = PageGetMaxOffsetNumber((Page) page) - FirstOffsetNumber + 1;
-
-		if (ScanDirectionIsForward(dir))
-			lineoff = FirstOffsetNumber;
-		else
-			lineoff = (OffsetNumber) linesleft;
+		page = heapgettup_start_page(scan, block, dir, &linesleft, &lineoff);
 	}
 	else
 	{
 		block = scan->rs_cblock; /* current page */
 
 		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
-
-		page = BufferGetPage(scan->rs_cbuf);
-		TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
-
-		if (ScanDirectionIsForward(dir))
-		{
-			lineoff = OffsetNumberNext(scan->rs_cindex);
-			/* block and lineoff now reference the physically next tid */
-			linesleft = PageGetMaxOffsetNumber(page) - lineoff + 1;
-		}
-		else
-		{
-			/*
-			 * The previous returned tuple may have been vacuumed since the
-			 * previous scan when we use a non-MVCC snapshot, so we must
-			 * re-establish the lineoff <= PageGetMaxOffsetNumber(page)
-			 * invariant
-			 */
-			lineoff = Min(PageGetMaxOffsetNumber(page), OffsetNumberPrev(scan->rs_cindex));
-			/* block and lineoff now reference the physically previous tid */
-			linesleft = lineoff;
-		}
+		page = heapgettup_continue_page(scan, block, dir, &linesleft, &lineoff);
 	}
 
 	/*
-- 
2.34.1