From 3ae5aa0401fc5028cc916d55c4b18e53bf6aa9fb Mon Sep 17 00:00:00 2001
From: Sokolov Yura <funny.falcon@postgrespro.ru>
Date: Mon, 15 May 2017 16:04:14 +0300
Subject: [PATCH 2/2] Simplify PageRepairFragmentation

In assumption that page usually doesn't become empty, merge second loop
body (collecting items with storage) into first (counting kinds of
items).
---
 src/backend/storage/page/bufpage.c | 47 +++++++++++++++-----------------------
 1 file changed, 19 insertions(+), 28 deletions(-)

diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index f28f18cff3..77cef51d02 100644
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -497,6 +497,7 @@ sort_itemIds(itemIdSort itemidbase, int nitems)
 
 	if (max == 1)
 		goto end;
+
 	/*
 	 * count[k+2] is start of bucket k, count[k+1] is end of bucket k, and
 	 * count[k+1]-count[k+2] is length of bucket k.
@@ -563,10 +564,11 @@ PageRepairFragmentation(Page page)
 	Offset		pd_special = ((PageHeader) page)->pd_special;
 	ItemId		lp;
 	int			nline,
-				nstorage,
 				nunused;
 	int			i;
 	Size		totallen;
+	itemIdSortData itemidbase[MaxHeapTuplesPerPage];
+	itemIdSort	itemidptr = itemidbase;
 
 	/*
 	 * It's worth the trouble to be more paranoid here than in most places,
@@ -586,14 +588,26 @@ PageRepairFragmentation(Page page)
 						pd_lower, pd_upper, pd_special)));
 
 	nline = PageGetMaxOffsetNumber(page);
-	nunused = nstorage = 0;
+	nunused = totallen = 0;
 	for (i = FirstOffsetNumber; i <= nline; i++)
 	{
 		lp = PageGetItemId(page, i);
 		if (ItemIdIsUsed(lp))
 		{
 			if (ItemIdHasStorage(lp))
-				nstorage++;
+			{
+				itemidptr->offsetindex = i - 1;
+				itemidptr->itemoff = ItemIdGetOffset(lp);
+				if (unlikely(itemidptr->itemoff < (int) pd_upper ||
+							 itemidptr->itemoff >= (int) pd_special))
+					ereport(ERROR,
+							(errcode(ERRCODE_DATA_CORRUPTED),
+							 errmsg("corrupted item pointer: %u",
+									itemidptr->itemoff)));
+				itemidptr->alignedlen = MAXALIGN(ItemIdGetLength(lp));
+				totallen += itemidptr->alignedlen;
+				itemidptr++;
+			}
 		}
 		else
 		{
@@ -603,7 +617,7 @@ PageRepairFragmentation(Page page)
 		}
 	}
 
-	if (nstorage == 0)
+	if (itemidptr == itemidbase)
 	{
 		/* Page is completely empty, so just reset it quickly */
 		((PageHeader) page)->pd_upper = pd_special;
@@ -611,36 +625,13 @@ PageRepairFragmentation(Page page)
 	else
 	{
 		/* Need to compact the page the hard way */
-		itemIdSortData itemidbase[MaxHeapTuplesPerPage];
-		itemIdSort	itemidptr = itemidbase;
-
-		totallen = 0;
-		for (i = 0; i < nline; i++)
-		{
-			lp = PageGetItemId(page, i + 1);
-			if (ItemIdHasStorage(lp))
-			{
-				itemidptr->offsetindex = i;
-				itemidptr->itemoff = ItemIdGetOffset(lp);
-				if (itemidptr->itemoff < (int) pd_upper ||
-					itemidptr->itemoff >= (int) pd_special)
-					ereport(ERROR,
-							(errcode(ERRCODE_DATA_CORRUPTED),
-							 errmsg("corrupted item pointer: %u",
-									itemidptr->itemoff)));
-				itemidptr->alignedlen = MAXALIGN(ItemIdGetLength(lp));
-				totallen += itemidptr->alignedlen;
-				itemidptr++;
-			}
-		}
-
 		if (totallen > (Size) (pd_special - pd_lower))
 			ereport(ERROR,
 					(errcode(ERRCODE_DATA_CORRUPTED),
 					 errmsg("corrupted item lengths: total %u, available space %u",
 							(unsigned int) totallen, pd_special - pd_lower)));
 
-		compactify_tuples(itemidbase, nstorage, page);
+		compactify_tuples(itemidbase, (int) (itemidptr - itemidbase), page);
 	}
 
 	/* Set hint bit for PageAddItem */
-- 
2.11.0