- Add check of already changed page while replay WAL. This touches only

ginRedoInsert(), because other ginRedo* functions rewrite whole page or
make changes which could be applied several times without consistent's loss

- Remove check of identifying of corresponding split record:
it's possible that replaying of WAL starts after actual page split, but before
removing of that split from incomplete splits list. In this case, that check
cause FATAL error.

Per stress test which reproduces bug reported by Craig McElroy
<craig.mcelroy@contegix.com>

src/backend/access/gin/ginxlog.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			 $PostgreSQL: pgsql/src/backend/access/gin/ginxlog.c,v 1.9 2007/09/20 17:56:30 tgl Exp $
+ *			 $PostgreSQL: pgsql/src/backend/access/gin/ginxlog.c,v 1.10 2007/10/29 19:26:57 teodor Exp $
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
@@ -53,7 +53,6 @@ static void
 forgetIncompleteSplit(RelFileNode node, BlockNumber leftBlkno, BlockNumber updateBlkno)
 {
 	ListCell   *l;
-	bool		found = false;
 
 	foreach(l, incomplete_splits)
 	{
@@ -62,16 +61,9 @@ forgetIncompleteSplit(RelFileNode node, BlockNumber leftBlkno, BlockNumber updat
 		if (RelFileNodeEquals(node, split->node) && leftBlkno == split->leftBlkno && updateBlkno == split->rightBlkno)
 		{
 			incomplete_splits = list_delete_ptr(incomplete_splits, split);
-			found = true;
 			break;
 		}
 	}
-
-	if (!found)
-	{
-		elog(ERROR, "failed to identify corresponding split record for %u/%u/%u",
-					node.relNode, leftBlkno, updateBlkno);
-	}
 }
 
 static void
@@ -129,7 +121,7 @@ ginRedoInsert(XLogRecPtr lsn, XLogRecord *record)
 	Buffer		buffer;
 	Page		page;
 
-	/* nothing else to do if page was backed up (and no info to do it with) */
+	/* nothing else to do if page was backed up */
 	if (record->xl_info & XLR_BKP_BLOCK_1)
 		return;
 
@@ -143,37 +135,44 @@ ginRedoInsert(XLogRecPtr lsn, XLogRecord *record)
 		Assert(data->isDelete == FALSE);
 		Assert(GinPageIsData(page));
 
-		if (data->isLeaf)
+		if ( ! XLByteLE(lsn, PageGetLSN(page)) )
 		{
-			OffsetNumber i;
-			ItemPointerData *items = (ItemPointerData *) (XLogRecGetData(record) + sizeof(ginxlogInsert));
+			if (data->isLeaf)
+			{
+				OffsetNumber i;
+				ItemPointerData *items = (ItemPointerData *) (XLogRecGetData(record) + sizeof(ginxlogInsert));
 
-			Assert(GinPageIsLeaf(page));
-			Assert(data->updateBlkno == InvalidBlockNumber);
+				Assert(GinPageIsLeaf(page));
+				Assert(data->updateBlkno == InvalidBlockNumber);
 
-			for (i = 0; i < data->nitem; i++)
-				GinDataPageAddItem(page, items + i, data->offset + i);
-		}
-		else
-		{
-			PostingItem *pitem;
+				for (i = 0; i < data->nitem; i++)
+					GinDataPageAddItem(page, items + i, data->offset + i);
+			}
+			else
+			{
+				PostingItem *pitem;
 
-			Assert(!GinPageIsLeaf(page));
+				Assert(!GinPageIsLeaf(page));
 
-			if (data->updateBlkno != InvalidBlockNumber)
-			{
-				/* update link to right page after split */
-				pitem = (PostingItem *) GinDataPageGetItem(page, data->offset);
-				PostingItemSetBlockNumber(pitem, data->updateBlkno);
-			}
+				if (data->updateBlkno != InvalidBlockNumber)
+				{
+					/* update link to right page after split */
+					pitem = (PostingItem *) GinDataPageGetItem(page, data->offset);
+					PostingItemSetBlockNumber(pitem, data->updateBlkno);
+				}
 
-			pitem = (PostingItem *) (XLogRecGetData(record) + sizeof(ginxlogInsert));
+				pitem = (PostingItem *) (XLogRecGetData(record) + sizeof(ginxlogInsert));
 
-			GinDataPageAddItem(page, pitem, data->offset);
+				GinDataPageAddItem(page, pitem, data->offset);
+			}
+		}
 
-			if (data->updateBlkno != InvalidBlockNumber)
-				forgetIncompleteSplit(data->node, PostingItemGetBlockNumber(pitem), data->updateBlkno);
+		if (!data->isLeaf && data->updateBlkno != InvalidBlockNumber)
+		{
+			PostingItem *pitem = (PostingItem *) (XLogRecGetData(record) + sizeof(ginxlogInsert));
+			forgetIncompleteSplit(data->node, PostingItemGetBlockNumber(pitem), data->updateBlkno);
 		}
+
 	}
 	else
 	{
@@ -181,36 +180,45 @@ ginRedoInsert(XLogRecPtr lsn, XLogRecord *record)
 
 		Assert(!GinPageIsData(page));
 
-		if (data->updateBlkno != InvalidBlockNumber)
+		if ( ! XLByteLE(lsn, PageGetLSN(page)) )
 		{
-			/* update link to right page after split */
-			Assert(!GinPageIsLeaf(page));
-			Assert(data->offset >= FirstOffsetNumber && data->offset <= PageGetMaxOffsetNumber(page));
-			itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, data->offset));
-			ItemPointerSet(&itup->t_tid, data->updateBlkno, InvalidOffsetNumber);
-		}
+			if (data->updateBlkno != InvalidBlockNumber)
+			{
+				/* update link to right page after split */
+				Assert(!GinPageIsLeaf(page));
+				Assert(data->offset >= FirstOffsetNumber && data->offset <= PageGetMaxOffsetNumber(page));
+				itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, data->offset));
+				ItemPointerSet(&itup->t_tid, data->updateBlkno, InvalidOffsetNumber);
+			}
 
-		if (data->isDelete)
-		{
-			Assert(GinPageIsLeaf(page));
-			Assert(data->offset >= FirstOffsetNumber && data->offset <= PageGetMaxOffsetNumber(page));
-			PageIndexTupleDelete(page, data->offset);
-		}
+			if (data->isDelete)
+			{
+				Assert(GinPageIsLeaf(page));
+				Assert(data->offset >= FirstOffsetNumber && data->offset <= PageGetMaxOffsetNumber(page));
+				PageIndexTupleDelete(page, data->offset);
+			}
 
-		itup = (IndexTuple) (XLogRecGetData(record) + sizeof(ginxlogInsert));
+			itup = (IndexTuple) (XLogRecGetData(record) + sizeof(ginxlogInsert));
 
-		if (PageAddItem(page, (Item) itup, IndexTupleSize(itup), data->offset, false, false) == InvalidOffsetNumber)
-			elog(ERROR, "failed to add item to index page in %u/%u/%u",
-				 data->node.spcNode, data->node.dbNode, data->node.relNode);
+			if (PageAddItem(page, (Item) itup, IndexTupleSize(itup), data->offset, false, false) == InvalidOffsetNumber)
+				elog(ERROR, "failed to add item to index page in %u/%u/%u",
+					 data->node.spcNode, data->node.dbNode, data->node.relNode);
+		}
 
 		if (!data->isLeaf && data->updateBlkno != InvalidBlockNumber)
+		{
+			itup = (IndexTuple) (XLogRecGetData(record) + sizeof(ginxlogInsert));
 			forgetIncompleteSplit(data->node, GinItemPointerGetBlockNumber(&itup->t_tid), data->updateBlkno);
+		}
 	}
 
-	PageSetLSN(page, lsn);
-	PageSetTLI(page, ThisTimeLineID);
+	if ( ! XLByteLE(lsn, PageGetLSN(page)) ) 
+	{
+		PageSetLSN(page, lsn);
+		PageSetTLI(page, ThisTimeLineID);
 
-	MarkBufferDirty(buffer);
+		MarkBufferDirty(buffer);
+	}
 	UnlockReleaseBuffer(buffer);
 }