* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.49 2007/01/05 22:19:24 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.50 2007/05/02 23:18:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* If "init" is true then the caller intends to rewrite the page fully
* using the info in the XLOG record. In this case we will extend the
* relation if needed to make the page exist, and we will not complain about
- * the page being "new" (all zeroes).
+ * the page being "new" (all zeroes); in fact, we usually will supply a
+ * zeroed buffer without reading the page at all, so as to avoid unnecessary
+ * failure if the page is present on disk but has corrupt headers.
*
* If "init" is false then the caller needs the page to be valid already.
* If the page doesn't exist or contains zeroes, we return InvalidBuffer.
if (blkno < lastblock)
{
/* page exists in file */
- buffer = ReadBuffer(reln, blkno);
+ if (init)
+ buffer = ReadOrZeroBuffer(reln, blkno);
+ else
+ buffer = ReadBuffer(reln, blkno);
}
else
{
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.216 2007/03/30 18:34:55 mha Exp $
+ * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.217 2007/05/02 23:18:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* and pin it so that no one can destroy it while this process
* is using it.
*
+ * ReadOrZeroBuffer() -- like ReadBuffer, but if the page is not already in
+ * cache we don't read it, but just return a zeroed-out buffer. Useful
+ * when the caller intends to fill the page from scratch, since this
+ * saves I/O and avoids unnecessary failure if the page-on-disk has
+ * corrupt page headers.
+ *
* ReleaseBuffer() -- unpin a buffer
*
* MarkBufferDirty() -- mark a pinned buffer's contents as "dirty".
extern PgStat_MsgBgWriter BgWriterStats;
+static Buffer ReadBuffer_common(Relation reln, BlockNumber blockNum,
+ bool zeroPage);
static bool PinBuffer(volatile BufferDesc *buf);
static void PinBuffer_Locked(volatile BufferDesc *buf);
static void UnpinBuffer(volatile BufferDesc *buf,
*/
Buffer
ReadBuffer(Relation reln, BlockNumber blockNum)
+{
+ return ReadBuffer_common(reln, blockNum, false);
+}
+
+/*
+ * ReadOrZeroBuffer -- like ReadBuffer, but if the page isn't in buffer
+ * cache already, it's filled with zeros instead of reading it from
+ * disk. The caller is expected to overwrite the whole buffer,
+ * so that the current page contents are not interesting.
+ */
+Buffer
+ReadOrZeroBuffer(Relation reln, BlockNumber blockNum)
+{
+ return ReadBuffer_common(reln, blockNum, true);
+}
+
+/*
+ * ReadBuffer_common -- common logic for ReadBuffer and ReadOrZeroBuffer
+ */
+static Buffer
+ReadBuffer_common(Relation reln, BlockNumber blockNum, bool zeroPage)
{
volatile BufferDesc *bufHdr;
Block bufBlock;
}
else
{
- smgrread(reln->rd_smgr, blockNum, (char *) bufBlock);
+ /*
+ * Read in the page, unless the caller intends to overwrite it
+ * and just wants us to allocate a buffer.
+ */
+ if (zeroPage)
+ MemSet((char *) bufBlock, 0, BLCKSZ);
+ else
+ smgrread(reln->rd_smgr, blockNum, (char *) bufBlock);
/* check for garbage data */
if (!PageHeaderIsValid((PageHeader) bufBlock))
{
- /*
- * During WAL recovery, the first access to any data page should
- * overwrite the whole page from the WAL; so a clobbered page
- * header is not reason to fail. Hence, when InRecovery we may
- * always act as though zero_damaged_pages is ON.
- */
- if (zero_damaged_pages || InRecovery)
+ if (zero_damaged_pages)
{
ereport(WARNING,
(errcode(ERRCODE_DATA_CORRUPTED),
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.102 2007/01/05 22:19:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.103 2007/05/02 23:18:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* prototypes for functions in bufmgr.c
*/
extern Buffer ReadBuffer(Relation reln, BlockNumber blockNum);
+extern Buffer ReadOrZeroBuffer(Relation reln, BlockNumber blockNum);
extern void ReleaseBuffer(Buffer buffer);
extern void UnlockReleaseBuffer(Buffer buffer);
extern void MarkBufferDirty(Buffer buffer);