Refactor per-page logic common to all redo routines to a new function.

Every redo routine uses the same idiom to determine what to do to a page:
check if there's a backup block for it, and if not read, the buffer if the
block exists, and check its LSN. Refactor that into a common function,
XLogReadBufferForRedo, making all the redo routines shorter and more
readable.

This has no user-visible effect, and makes no changes to the WAL format.

Reviewed by Andres Freund, Alvaro Herrera, Michael Paquier.

1 files changed, 78 insertions, 101 deletions

diff --git a/src/backend/access/gist/gistxlog.c b/src/backend/access/gist/gistxlog.c
index 7d36b2ab6a3..ecc095671df 100644
--- a/src/backend/access/gist/gistxlog.c
+++ b/src/backend/access/gist/gistxlog.c
@@ -48,31 +48,26 @@ gistRedoClearFollowRight(XLogRecPtr lsn, XLogRecord *record, int block_index,
 {
 	Buffer		buffer;
 	Page		page;
-
-	if (record->xl_info & XLR_BKP_BLOCK(block_index))
-		buffer = RestoreBackupBlock(lsn, record, block_index, false, true);
-	else
-	{
-		buffer = XLogReadBuffer(node, childblkno, false);
-		if (!BufferIsValid(buffer))
-			return;				/* page was deleted, nothing to do */
-	}
-	page = (Page) BufferGetPage(buffer);
+	XLogRedoAction action;
 
 	/*
-	 * Note that we still update the page even if page LSN is equal to the LSN
-	 * of this record, because the updated NSN is not included in the full
-	 * page image.
+	 * Note that we still update the page even if it was restored from a full
+	 * page image, because the updated NSN is not included in the image.
 	 */
-	if (lsn >= PageGetLSN(page))
+	action = XLogReadBufferForRedo(lsn, record, block_index, node, childblkno,
+								   &buffer);
+	if (action == BLK_NEEDS_REDO || action == BLK_RESTORED)
 	{
+		page = BufferGetPage(buffer);
+
 		GistPageSetNSN(page, lsn);
 		GistClearFollowRight(page);
 
 		PageSetLSN(page, lsn);
 		MarkBufferDirty(buffer);
 	}
-	UnlockReleaseBuffer(buffer);
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
 }
 
 /*
@@ -87,104 +82,86 @@ gistRedoPageUpdateRecord(XLogRecPtr lsn, XLogRecord *record)
 	Page		page;
 	char	   *data;
 
-	/*
-	 * We need to acquire and hold lock on target page while updating the left
-	 * child page.  If we have a full-page image of target page, getting the
-	 * lock is a side-effect of restoring that image.  Note that even if the
-	 * target page no longer exists, we'll still attempt to replay the change
-	 * on the child page.
-	 */
-	if (record->xl_info & XLR_BKP_BLOCK(0))
-		buffer = RestoreBackupBlock(lsn, record, 0, false, true);
-	else
-		buffer = XLogReadBuffer(xldata->node, xldata->blkno, false);
-
-	/* Fix follow-right data on left child page */
-	if (BlockNumberIsValid(xldata->leftchild))
-		gistRedoClearFollowRight(lsn, record, 1,
-								 xldata->node, xldata->leftchild);
-
-	/* Done if target page no longer exists */
-	if (!BufferIsValid(buffer))
-		return;
-
-	/* nothing more to do if page was backed up (and no info to do it with) */
-	if (record->xl_info & XLR_BKP_BLOCK(0))
+	if (XLogReadBufferForRedo(lsn, record, 0, xldata->node, xldata->blkno,
+							  &buffer) == BLK_NEEDS_REDO)
 	{
-		UnlockReleaseBuffer(buffer);
-		return;
-	}
-
-	page = (Page) BufferGetPage(buffer);
-
-	/* nothing more to do if change already applied */
-	if (lsn <= PageGetLSN(page))
-	{
-		UnlockReleaseBuffer(buffer);
-		return;
-	}
-
-	data = begin + sizeof(gistxlogPageUpdate);
+		page = (Page) BufferGetPage(buffer);
 
-	/* Delete old tuples */
-	if (xldata->ntodelete > 0)
-	{
-		int			i;
-		OffsetNumber *todelete = (OffsetNumber *) data;
+		data = begin + sizeof(gistxlogPageUpdate);
 
-		data += sizeof(OffsetNumber) * xldata->ntodelete;
+		/* Delete old tuples */
+		if (xldata->ntodelete > 0)
+		{
+			int			i;
+			OffsetNumber *todelete = (OffsetNumber *) data;
 
-		for (i = 0; i < xldata->ntodelete; i++)
-			PageIndexTupleDelete(page, todelete[i]);
-		if (GistPageIsLeaf(page))
-			GistMarkTuplesDeleted(page);
-	}
+			data += sizeof(OffsetNumber) * xldata->ntodelete;
 
-	/* add tuples */
-	if (data - begin < record->xl_len)
-	{
-		OffsetNumber off = (PageIsEmpty(page)) ? FirstOffsetNumber :
-		OffsetNumberNext(PageGetMaxOffsetNumber(page));
+			for (i = 0; i < xldata->ntodelete; i++)
+				PageIndexTupleDelete(page, todelete[i]);
+			if (GistPageIsLeaf(page))
+				GistMarkTuplesDeleted(page);
+		}
 
-		while (data - begin < record->xl_len)
+		/* add tuples */
+		if (data - begin < record->xl_len)
 		{
-			IndexTuple	itup = (IndexTuple) data;
-			Size		sz = IndexTupleSize(itup);
-			OffsetNumber l;
-
-			data += sz;
+			OffsetNumber off = (PageIsEmpty(page)) ? FirstOffsetNumber :
+			OffsetNumberNext(PageGetMaxOffsetNumber(page));
+
+			while (data - begin < record->xl_len)
+			{
+				IndexTuple	itup = (IndexTuple) data;
+				Size		sz = IndexTupleSize(itup);
+				OffsetNumber l;
+
+				data += sz;
+
+				l = PageAddItem(page, (Item) itup, sz, off, false, false);
+				if (l == InvalidOffsetNumber)
+					elog(ERROR, "failed to add item to GiST index page, size %d bytes",
+						 (int) sz);
+				off++;
+			}
+		}
+		else
+		{
+			/*
+			 * special case: leafpage, nothing to insert, nothing to delete,
+			 * then vacuum marks page
+			 */
+			if (GistPageIsLeaf(page) && xldata->ntodelete == 0)
+				GistClearTuplesDeleted(page);
+		}
 
-			l = PageAddItem(page, (Item) itup, sz, off, false, false);
-			if (l == InvalidOffsetNumber)
-				elog(ERROR, "failed to add item to GiST index page, size %d bytes",
-					 (int) sz);
-			off++;
+		if (!GistPageIsLeaf(page) &&
+			PageGetMaxOffsetNumber(page) == InvalidOffsetNumber &&
+			xldata->blkno == GIST_ROOT_BLKNO)
+		{
+			/*
+			 * all links on non-leaf root page was deleted by vacuum full, so
+			 * root page becomes a leaf
+			 */
+			GistPageSetLeaf(page);
 		}
-	}
-	else
-	{
-		/*
-		 * special case: leafpage, nothing to insert, nothing to delete, then
-		 * vacuum marks page
-		 */
-		if (GistPageIsLeaf(page) && xldata->ntodelete == 0)
-			GistClearTuplesDeleted(page);
-	}
 
-	if (!GistPageIsLeaf(page) &&
-		PageGetMaxOffsetNumber(page) == InvalidOffsetNumber &&
-		xldata->blkno == GIST_ROOT_BLKNO)
-	{
-		/*
-		 * all links on non-leaf root page was deleted by vacuum full, so root
-		 * page becomes a leaf
-		 */
-		GistPageSetLeaf(page);
+		PageSetLSN(page, lsn);
+		MarkBufferDirty(buffer);
 	}
 
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(buffer);
-	UnlockReleaseBuffer(buffer);
+	/*
+	 * Fix follow-right data on left child page
+	 *
+	 * This must be done while still holding the lock on the target page. Note
+	 * that even if the target page no longer exists, we still attempt to
+	 * replay the change on the child page.
+	 */
+	if (BlockNumberIsValid(xldata->leftchild))
+		gistRedoClearFollowRight(lsn, record, 1,
+								 xldata->node, xldata->leftchild);
+
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
 }
 
 static void