<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.147.2.6 2003/01/11 05:04:26 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.147.2.7 2003/04/04 00:32:57 tgl Exp $
-->
<Chapter Id="runtime">
</para>
<para>
- It should be noted that the performance penalty of doing
- <function>fsync</>s is considerably less in
+ It should be noted that the performance penalty of having
+ <function>fsync</> on is considerably less in
<productname>PostgreSQL</> version 7.1 and later. If you
- previously suppressed <function>fsync</>s for performance
+ previously suppressed <function>fsync</> for performance
reasons, you may wish to reconsider your choice.
</para>
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>ZERO_DAMAGED_PAGES</varname> (<type>boolean</type>)</term>
+ <listitem>
+ <para>
+ Detection of a damaged page header normally causes
+ <productname>PostgreSQL</> to report an error, aborting the current
+ transaction. Setting <varname>zero_damaged_pages</> to true causes
+ the system to instead report a warning, zero out the damaged page,
+ and continue processing. This behavior <emphasis>will destroy data</>,
+ namely all the rows on the damaged page. But it allows you to get
+ past the error and retrieve rows from any undamaged pages that may
+ be present in the table. So it is useful for recovering data if
+ corruption has occurred due to hardware or software error. You should
+ generally not set this true until you have given up hope of recovering
+ data from the damaged page(s) of a table. The
+ default setting is off, and it can only be changed by a superuser.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</para>
</sect2>
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.133 2002/09/14 19:59:20 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.133.2.1 2003/04/04 00:32:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "miscadmin.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
+#include "storage/bufpage.h"
#include "storage/proc.h"
#include "storage/smgr.h"
#include "utils/relcache.h"
(*((XLogRecPtr*) MAKE_PTR((bufHdr)->data)))
+/* GUC variable */
+bool zero_damaged_pages = false;
+
+
static void WaitIO(BufferDesc *buf);
static void StartBufferIO(BufferDesc *buf, bool forInput);
static void TerminateBufferIO(BufferDesc *buf);
{
status = smgrread(DEFAULT_SMGR, reln, blockNum,
(char *) MAKE_PTR(bufHdr->data));
+ /* check for garbage data */
+ if (status == SM_SUCCESS &&
+ !PageHeaderIsValid((PageHeader) MAKE_PTR(bufHdr->data)))
+ {
+ if (zero_damaged_pages)
+ {
+ elog(WARNING, "Invalid page header in block %u of %s; zeroing out page",
+ blockNum, RelationGetRelationName(reln));
+ MemSet((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
+ }
+ else
+ elog(ERROR, "Invalid page header in block %u of %s",
+ blockNum, RelationGetRelationName(reln));
+ }
}
if (isLocalBuf)
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/page/bufpage.c,v 1.50 2002/09/04 20:31:26 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/page/bufpage.c,v 1.50.2.1 2003/04/04 00:32:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
-#include <sys/file.h>
-
#include "storage/bufpage.h"
}
+/*
+ * PageHeaderIsValid
+ * Check that the header fields of a page appear valid.
+ *
+ * This is called when a page has just been read in from disk. The idea is
+ * to cheaply detect trashed pages before we go nuts following bogus item
+ * pointers, testing invalid transaction identifiers, etc.
+ *
+ * It turns out to be necessary to allow zeroed pages here too. Even though
+ * this routine is *not* called when deliberately adding a page to a relation,
+ * there are scenarios in which a zeroed page might be found in a table.
+ * (Example: a backend extends a relation, then crashes before it can write
+ * any WAL entry about the new page. The kernel will already have the
+ * zeroed page in the file, and it will stay that way after restart.) So we
+ * allow zeroed pages here, and are careful that the page access macros
+ * treat such a page as empty and without free space. Eventually, VACUUM
+ * will clean up such a page and make it usable.
+ */
+bool
+PageHeaderIsValid(PageHeader page)
+{
+ char *pagebytes;
+ int i;
+
+ /* Check normal case */
+ if (PageGetPageSize(page) == BLCKSZ &&
+ PageGetPageLayoutVersion(page) == PG_PAGE_LAYOUT_VERSION &&
+ page->pd_lower >= SizeOfPageHeaderData &&
+ page->pd_lower <= page->pd_upper &&
+ page->pd_upper <= page->pd_special &&
+ page->pd_special <= BLCKSZ &&
+ page->pd_special == MAXALIGN(page->pd_special))
+ return true;
+
+ /* Check all-zeroes case */
+ pagebytes = (char *) page;
+ for (i = 0; i < BLCKSZ; i++)
+ {
+ if (pagebytes[i] != 0)
+ return false;
+ }
+ return true;
+}
+
+
/* ----------------
* PageAddItem
*
* command, configuration file, and command line options.
* See src/backend/utils/misc/README for more information.
*
- * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.99.2.4 2003/01/28 18:04:13 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.99.2.5 2003/04/04 00:32:57 tgl Exp $
*
* Copyright 2000 by PostgreSQL Global Development Group
* Written by Peter Eisentraut <peter_e@gmx.net>.
{"fsync", PGC_SIGHUP}, &enableFsync,
true, NULL, NULL
},
+ {
+ {"zero_damaged_pages", PGC_SUSET}, &zero_damaged_pages,
+ false, NULL, NULL
+ },
{
{"silent_mode", PGC_POSTMASTER}, &SilentMode,
false, NULL, NULL
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: bufmgr.h,v 1.66 2002/10/22 20:00:48 petere Exp $
+ * $Id: bufmgr.h,v 1.66.2.1 2003/04/04 00:32:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/* in globals.c ... this duplicates miscadmin.h */
extern DLLIMPORT int NBuffers;
+/* in bufmgr.c */
+extern bool zero_damaged_pages;
+
/* in buf_init.c */
extern DLLIMPORT Block *BufferBlockPointers;
extern long *PrivateRefCount;
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: bufpage.h,v 1.53 2002/09/04 20:31:45 momjian Exp $
+ * $Id: bufpage.h,v 1.53.2.1 2003/04/04 00:32:57 tgl Exp $
*
*-------------------------------------------------------------------------
*/
*/
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, ItemIdFlags flags);
extern Page PageGetTempPage(Page page, Size specialSize);
projects / thirdparty / postgresql.git / commitdiff
