Clean up the messy semantics (not to mention inefficiency) of PageGetTempPage

by splitting it into three functions with better-defined behaviors.

Zdenek Kotala

src/backend/access/gin/gindatapage.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/gindatapage.c,v 1.11 2008/06/19 00:46:03 alvherre Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/gindatapage.c,v 1.12 2008/11/03 20:47:48 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -445,7 +445,7 @@ dataSplitPage(GinBtree btree, Buffer lbuf, Buffer rbuf, OffsetNumber off, XLogRe
 	char	   *ptr;
 	OffsetNumber separator;
 	ItemPointer bound;
-	Page		lpage = GinPageGetCopyPage(BufferGetPage(lbuf));
+	Page		lpage = PageGetTempPageCopy(BufferGetPage(lbuf));
 	ItemPointerData oldbound = *GinDataPageGetRightBound(lpage);
 	int			sizeofitem = GinSizeOfItem(lpage);
 	OffsetNumber maxoff = GinPageGetOpaque(lpage)->maxoff;

src/backend/access/gin/ginentrypage.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginentrypage.c,v 1.17 2008/07/11 21:06:29 tgl Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginentrypage.c,v 1.18 2008/11/03 20:47:48 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -458,7 +458,7 @@ entrySplitPage(GinBtree btree, Buffer lbuf, Buffer rbuf, OffsetNumber off, XLogR
 				leftrightmost = NULL;
 	static ginxlogSplit data;
 	Page		page;
-	Page		lpage = GinPageGetCopyPage(BufferGetPage(lbuf));
+	Page		lpage = PageGetTempPageCopy(BufferGetPage(lbuf));
 	Page		rpage = BufferGetPage(rbuf);
 	Size		pageSize = PageGetPageSize(lpage);
 

src/backend/access/gin/ginutil.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginutil.c,v 1.17 2008/09/30 10:52:10 heikki Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginutil.c,v 1.18 2008/11/03 20:47:48 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -310,21 +310,6 @@ extractEntriesSU(GinState *ginstate, OffsetNumber attnum, Datum value, int32 *ne
 	return entries;
 }
 
-/*
- * It's analog of PageGetTempPage(), but copies whole page
- */
-Page
-GinPageGetCopyPage(Page page)
-{
-	Size		pageSize = PageGetPageSize(page);
-	Page		tmppage;
-
-	tmppage = (Page) palloc(pageSize);
-	memcpy(tmppage, page, pageSize);
-
-	return tmppage;
-}
-
 Datum
 ginoptions(PG_FUNCTION_ARGS)
 {

src/backend/access/gin/ginvacuum.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.24 2008/10/31 15:04:59 heikki Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.25 2008/11/03 20:47:48 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -546,7 +546,7 @@ ginVacuumEntryPage(GinVacuumState *gvs, Buffer buffer, BlockNumber *roots, uint3
 					 * On first difference we create temporary page in memory
 					 * and copies content in to it.
 					 */
-					tmppage = GinPageGetCopyPage(origpage);
+					tmppage = PageGetTempPageCopy(origpage);
 
 					if (newN > 0)
 					{

src/backend/access/gist/gist.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gist.c,v 1.152 2008/09/30 10:52:10 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gist.c,v 1.153 2008/11/03 20:47:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -343,7 +343,7 @@ gistplacetopage(GISTInsertState *state, GISTSTATE *giststate)
 			 * we must create temporary page to operate
 			 */
 			dist->buffer = state->stack->buffer;
-			dist->page = PageGetTempPage(BufferGetPage(dist->buffer), sizeof(GISTPageOpaqueData));
+			dist->page = PageGetTempPageCopySpecial(BufferGetPage(dist->buffer));
 
 			/* clean all flags except F_LEAF */
 			GistPageGetOpaque(dist->page)->flags = (is_leaf) ? F_LEAF : 0;

src/backend/access/gist/gistvacuum.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/gist/gistvacuum.c,v 1.39 2008/10/31 15:04:59 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/gist/gistvacuum.c,v 1.40 2008/11/03 20:47:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -144,18 +144,6 @@ gistDeleteSubtree(GistVacuum *gv, BlockNumber blkno)
 	UnlockReleaseBuffer(buffer);
 }
 
-static Page
-GistPageGetCopyPage(Page page)
-{
-	Size		pageSize = PageGetPageSize(page);
-	Page		tmppage;
-
-	tmppage = (Page) palloc(pageSize);
-	memcpy(tmppage, page, pageSize);
-
-	return tmppage;
-}
-
 static ArrayTuple
 vacuumSplitPage(GistVacuum *gv, Page tempPage, Buffer buffer, IndexTuple *addon, int curlenaddon)
 {
@@ -325,7 +313,7 @@ gistVacuumUpdate(GistVacuum *gv, BlockNumber blkno, bool needunion)
 		addon = (IndexTuple *) palloc(sizeof(IndexTuple) * lenaddon);
 
 		/* get copy of page to work */
-		tempPage = GistPageGetCopyPage(page);
+		tempPage = PageGetTempPageCopy(page);
 
 		for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
 		{

src/backend/access/nbtree/nbtinsert.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.167 2008/06/11 08:38:56 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.168 2008/11/03 20:47:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -793,7 +793,7 @@ _bt_split(Relation rel, Buffer buf, OffsetNumber firstright,
 
 	rbuf = _bt_getbuf(rel, P_NEW, BT_WRITE);
 	origpage = BufferGetPage(buf);
-	leftpage = PageGetTempPage(origpage, sizeof(BTPageOpaqueData));
+	leftpage = PageGetTempPage(origpage);
 	rightpage = BufferGetPage(rbuf);
 
 	_bt_pageinit(leftpage, BufferGetPageSize(buf));

src/backend/storage/page/bufpage.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.80 2008/07/13 21:50:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.81 2008/11/03 20:47:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -254,28 +254,59 @@ PageAddItem(Page page,
 
 /*
  * PageGetTempPage
- *		Get a temporary page in local memory for special processing
+ *		Get a temporary page in local memory for special processing.
+ *		The returned page is not initialized at all; caller must do that.
  */
 Page
-PageGetTempPage(Page page, Size specialSize)
+PageGetTempPage(Page page)
+{
+	Size		pageSize;
+	Page		temp;
+
+	pageSize = PageGetPageSize(page);
+	temp = (Page) palloc(pageSize);
+
+	return temp;
+}
+
+/*
+ * PageGetTempPageCopy
+ *		Get a temporary page in local memory for special processing.
+ *		The page is initialized by copying the contents of the given page.
+ */
+Page
+PageGetTempPageCopy(Page page)
 {
 	Size		pageSize;
 	Page		temp;
-	PageHeader	thdr;
 
 	pageSize = PageGetPageSize(page);
 	temp = (Page) palloc(pageSize);
-	thdr = (PageHeader) temp;
 
-	/* copy old page in */
 	memcpy(temp, page, pageSize);
 
-	/* set high, low water marks */
-	thdr->pd_lower = SizeOfPageHeaderData;
-	thdr->pd_upper = pageSize - MAXALIGN(specialSize);
+	return temp;
+}
+
+/*
+ * PageGetTempPageCopySpecial
+ *		Get a temporary page in local memory for special processing.
+ *		The page is PageInit'd with the same special-space size as the
+ *		given page, and the special space is copied from the given page.
+ */
+Page
+PageGetTempPageCopySpecial(Page page)
+{
+	Size		pageSize;
+	Page		temp;
+
+	pageSize = PageGetPageSize(page);
+	temp = (Page) palloc(pageSize);
 
-	/* clear out the middle */
-	MemSet((char *) temp + thdr->pd_lower, 0, thdr->pd_upper - thdr->pd_lower);
+	PageInit(temp, pageSize, PageGetSpecialSize(page));
+	memcpy(PageGetSpecialPointer(temp),
+		   PageGetSpecialPointer(page),
+		   PageGetSpecialSize(page));
 
 	return temp;
 }

src/include/access/gin.h

@@ -4,7 +4,7 @@
  *
  *	Copyright (c) 2006-2008, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.25 2008/10/20 13:39:44 teodor Exp $
+ *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.26 2008/11/03 20:47:49 tgl Exp $
  *--------------------------------------------------------------------------
  */
 
@@ -246,7 +246,6 @@ extern int	compareAttEntries(GinState *ginstate, OffsetNumber attnum_a, Datum a,
 extern Datum *extractEntriesS(GinState *ginstate, OffsetNumber attnum, Datum value,
 				int32 *nentries, bool *needUnique);
 extern Datum *extractEntriesSU(GinState *ginstate, OffsetNumber attnum, Datum value, int32 *nentries);
-extern Page GinPageGetCopyPage(Page page);
 
 extern Datum gin_index_getattr(GinState *ginstate, IndexTuple tuple);
 extern OffsetNumber gintuple_get_attrnum(GinState *ginstate, IndexTuple tuple);

src/include/storage/bufpage.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.83 2008/07/14 03:22:32 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.84 2008/11/03 20:47:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -362,7 +362,9 @@ extern void PageInit(Page page, Size pageSize, Size specialSize);
 extern bool PageHeaderIsValid(PageHeader page);
 extern OffsetNumber PageAddItem(Page page, Item item, Size size,
 			OffsetNumber offsetNumber, bool overwrite, bool is_heap);
-extern Page PageGetTempPage(Page page, Size specialSize);
+extern Page PageGetTempPage(Page page);
+extern Page PageGetTempPageCopy(Page page);
+extern Page PageGetTempPageCopySpecial(Page page);
 extern void PageRestoreTempPage(Page tempPage, Page oldPage);
 extern void PageRepairFragmentation(Page page);
 extern Size PageGetFreeSpace(Page page);