<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.174 2003/03/25 16:15:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.175 2003/03/28 20:17:13 tgl Exp $
-->
<Chapter Id="runtime">
<para>
It should be noted that the performance penalty of having
- <varname>fsync</> on considerably less in
+ <varname>fsync</> on is considerably less in
<productname>PostgreSQL</> version 7.1 and later. If you
previously suppressed <function>fsync</> for performance
reasons, you may wish to reconsider your choice.
</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 lose 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. The
+ default setting is off, and it can only be changed by a superuser.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</sect2>
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.134 2003/02/13 05:35:11 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.135 2003/03/28 20:17:13 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 1.51 2003/01/11 05:01:03 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/page/bufpage.c,v 1.52 2003/03/28 20:17:13 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 1.117 2003/03/20 04:51:44 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc.c,v 1.118 2003/03/28 20:17:13 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
#sql_inheritance = true
#transform_null_equals = false
#statement_timeout = 0 # 0 is disabled, in milliseconds
+#zero_damaged_pages = false # set this true only for disaster recovery
#db_user_namespace = false
#preload_libraries = ''
-
* 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 1.67 2003/03/28 20:17:13 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 1.54 2003/03/28 20:17:13 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "storage/item.h"
#include "storage/itemid.h"
#include "storage/off.h"
-#include "storage/page.h"
#include "access/xlog.h"
/*
* fields.
*/
-/*
- * PageIsValid
- * True iff page is valid.
- */
-#define PageIsValid(page) PointerIsValid(page)
+typedef Pointer Page;
/*
* page support macros
* ----------------------------------------------------------------
*/
-/*
- * PageIsValid -- This is defined in page.h.
- */
/*
- * PageIsUsed
- * True iff the page size is used.
- *
- * Note:
- * Assumes page is valid.
+ * PageIsValid
+ * True iff page is valid.
*/
-#define PageIsUsed(page) \
-( \
- AssertMacro(PageIsValid(page)), \
- ((bool) (((PageHeader) (page))->pd_lower != 0)) \
-)
+#define PageIsValid(page) PointerIsValid(page)
/*
* line pointer does not count as part of header
/*
* PageIsNew
- * returns true iff page is not initialized (by PageInit)
+ * returns true iff page has not been initialized (by PageInit)
*/
-
#define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0)
/*
/*
* PageSizeIsValid
* True iff the page size is valid.
- *
- * XXX currently all page sizes are "valid" but we only actually
- * use BLCKSZ.
- *
- * 01/06/98 Now does something useful. darrenk
- *
*/
#define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ)
*
* this can only be called on a formatted page (unlike
* BufferGetPageSize, which can be called on an unformatted page).
- * however, it can be called on a page for which there is no buffer.
+ * however, it can be called on a page that is not stored in a buffer.
*/
#define PageGetPageSize(page) \
((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00))
/*
* PageGetPageLayoutVersion
* Returns the page layout version of a page.
- *
- * this can only be called on a formatted page (unlike
- * BufferGetPageSize, which can be called on an unformatted page).
- * however, it can be called on a page for which there is no buffer.
*/
#define PageGetPageLayoutVersion(page) \
(((PageHeader) (page))->pd_pagesize_version & 0x00FF)
/*
* PageGetSpecialSize
* Returns size of special space on a page.
- *
- * Note:
- * Assumes page is locked.
*/
#define PageGetSpecialSize(page) \
((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special))
/*
* PageGetSpecialPointer
* Returns pointer to special space on a page.
- *
- * Note:
- * Assumes page is locked.
*/
#define PageGetSpecialPointer(page) \
( \
*/
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);
+++ /dev/null
-/*-------------------------------------------------------------------------
- *
- * page.h
- * POSTGRES buffer page abstraction definitions.
- *
- *
- * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * $Id: page.h,v 1.12 2002/06/20 20:29:52 momjian Exp $
- *
- *-------------------------------------------------------------------------
- */
-#ifndef PAGE_H
-#define PAGE_H
-
-typedef Pointer Page;
-
-/*
- * PageIsValid
- * True iff page is valid.
- */
-#define PageIsValid(page) PointerIsValid(page)
-
-#endif /* PAGE_H */
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