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Handling Oracle Block Corruptions in Oracle7/8/8i/9i/10g/11g [ID 28814.1]

原创 Linux操作系统 作者:rongshiyuan 时间:2012-07-16 14:53:48 0 删除 编辑
https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&doctype=BULLETIN&id=28814.1
 
Handling Oracle Block Corruptions in Oracle7/8/8i/9i/10g/11g [ID 28814.1]

修改时间 11-JUL-2012 类型 BULLETIN 状态 PUBLISHED

Handling Block Corruptions in Oracle7 / 8 / 8i / 9i / 10g / 11g

Contents

Introduction Overview of Steps to handle a Corruption Corruption due to NOLOGGING or UNRECOVERABLE (1) Determine the Extent of the Corruption Problem (2) Replace or Move Away from Suspect Hardware (3) Which Objects are Affected ? Options for various Segment Types: CACHE CLUSTER INDEX PARTITION INDEX LOBINDEX LOBSEGMENT ROLLBACK TABLE PARTITION TABLE TEMPORARY IOT TYPE2 UNDO Other Segment Types No Segment (4) Choosing a Recovery Option (4A) Complete Recovery Block Level Recovery , Datafile Recovery , Database Recovery , After Complete Recovery (4B) Recreating Indexes (4C) Salvaging Data from Tables Methods of extracting data from a corrupt table AROUND a corrupt block Methods of extracting data from a table with a corrupt LOBSEGMENT block Extracting data from the corrupt block itself (4D) Leaving the Corruption in Place Warnings when Leaving a Corruption in Place (4E) Last Options Document History All SQL statements here are for use in SQL*Plus (in 8.1 or higher) or Server Manager (Oracle7 / 8.0) when connected as a SYSDBA user. (Eg: "connect / as sysdba" or "connect internal")

Introduction

This article discusses how to handle one or more block corruptions on an Oracle datafile and describes the main actions to take to deal with them. Please read the complete article before taking any action. This note does not cover memory corruption issues (typically ORA-600 [17xxx] type errors). Note: If the problem is an ORA-1578 on STARTUP then please contact your local support center for advice referencing Note:106638.1 - this note is not visible to customers but the relevant steps from it can be supplied by an experienced support analyst.

You may be referred to this article from many places for many forms of error - it is important that you have the following information for each corrupt block:

  • An absolute FILE NUMBER of the file containing the corrupt block. Referred to as "&AFN" in this article.
  • The file name of the file containing the corrupt block. Referred to as "&FILENAME" in this article. ( If you know the FILE NUMBER but not its name then V$DATAFILE can be used to get the file name: SELECT name FROM v$datafile WHERE file#=&AFN; If the file number does not appear in V$DATAFILE in Oracle8i AND &AFN is greater than the DB_FILES parameter value then it is probably a TEMPFILE. In this case the filename can be found using: SELECT name FROM v$tempfile WHERE file#=(&AFN - &DB_FILES_value); )
  • The BLOCK NUMBER of the corrupt block in that file. Referred to as "&BL" in this article.
  • The tablespace number and name containing the affected block. Referred to as "&TSN" (tablespace number) and "&TABLESPACE_NAME" in this article. If you do not know these then you can find them using: SELECT ts# "TSN" FROM v$datafile WHERE file#=&AFN; SELECT tablespace_name FROM dba_data_files WHERE file_id=&AFN;
  • The block size of the tablespace where the corruption lies. Referred to as "&TS_BLOCK_SIZE" in this article. For Oracle 9i+, run the following query to determine the appropriate block size: SELECT block_size FROM dba_tablespaces WHERE tablespace_name = (SELECT tablespace_name FROM dba_data_files WHERE file_id=&AFN); For Oracle 7, 8.0 and 8.1: Every tablespace in the database has the same block size. For these versions, issue "SHOW PARAMETER DB_BLOCK_SIZE" and use this value as your &TS_BLOCK_SIZE.
Eg: For the ORA-1578 error: ORA-01578: ORACLE data block corrupted (file # 7, block # 12698) ORA-01110: data file 22: '/oracle1/oradata/V816/oradata/V816/users01.dbf' then: &AFN is "22" (from the ORA-1110 portion of the error) &RFN is "7" (from the "file #" in the ORA-1578) &BL is "12698" (from the "block #" in the ORA-1578) &FILENAME is '/oracle1/oradata/V816/oradata/V816/users01.dbf' &TSN etc.. should be determined from the above SQL For other errors (ORA-600 , ORA-1498 etc...) the above values should either be given to you by Oracle Support, or be given to you from the article which covers the relevant error. Some errors, such as ORA-1410 "invalid ROWID" , ORA-12899 "value too large for column" etc.., do not give details of the corrupt file / block. For such cases Note:869305.1 may help in locating the corrupt row.

Overview of Steps to handle a Corruption

There are many possible causes of a block corruption including: - Bad IO hardware / firmware - OS problems - Oracle problems - Recovering through "UNRECOVERABLE" or "NOLOGGING" database actions (in which case ORA-1578 is expected behaviour - see below) The point in time when an Oracle error is raised may be much later than when any corruption initially occurred. As the root cause is not usually known at the time the corruption is encountered, and as in most cases the key requirement is to get up and running again, then the steps used tackle corruption problems in this article are: 1) Determine the extent of the corruption problems and also determine if the problems are permanent or transient. If the problem is widespread or the errors move about then focus on identifying the cause first (check hardware etc..). This is important as there is no point recovering a system if the underlying hardware is faulty. 2) Replace or move away from any faulty or suspect hardware. 3) Determine which database objects are affected. 4) Choose the most appropriate database recovery / data salvage option. For all steps above it is sensible to collect evidence and document exactly what actions are being taken. The 'Evidence>>' tags in this article list the information which should be collected to assist with identifying the root cause of the problem. Corruption due to NOLOGGING or UNRECOVERABLE If a NOLOGGING (or UNRECOVERABLE) operation is performed on an object and the datafile containing that object is subsequently recovered then the data blocks affected by the NOLOGGING operation are marked as corrupt and will signal an ORA-1578 error when accessed. In Oracle8i an ORA-26040 is also signalled ("ORA-26040: Data block was loaded using the NOLOGGING option" ) which makes the cause fairly obvious, but earlier releases have no additional error message. If a block is corrupt due to recovery through a NOLOGGING operation then you can use this article from Section 3 "Which Objects are Affected ?" onwards but note that: (a) Recovery cannot retrieve the NOLOGGING data (b) No data is salvagable from inside the block

(1) Determine the Extent of the Corruption Problem

Whenever a corruption error occurs note down the FULL error message/s and look in the instance's alert log and trace files for any associated errors. It is important to do this first to assess whether this is a single block corruption, an error due to an UNRECOVERABLE operation or a more severe issue. It is a good idea to scan affected files (and any important files) with DBVERIFY to check for other corruptions in order to determine the extent of the problem. For details of using DBVERIFY see Note:35512.1 Once you have determined a list of corrupt file/block combinations then the steps below can be used to help determine what action can be taken. Evidence>> - Record the original error in full, along with details of the application which encountered the error. - Save an extract from the alert log from a few hours before the FIRST recorded problem up to the current point in time. - Save any tracefiles mentioned in the alert log. - Record any recent OS problems you have encountered. - Note if you are using any special features - Eg: ASYNC IO, fast write disk options etc.. - Record your current BACKUP position (Dates, Type etc...) - Note if your database is in ARCHIVELOG mode or not Eg: Issue "ARCHIVE LOG LIST" in SQL*Plus (or Server Manager)

(2) Replace or Move Away from Suspect Hardware

The vast majority of corruption problems are caused by faulty hardware. If there is a hardware fault or a suspect component then it is sensible to either repair the problem, or make disk space available on a separate disk sub-system prior to proceeding with a recovery option. You can move datafiles about using the following steps: 1. Make sure the file to be relocated is either OFFLINE or the instance is in the MOUNT state (not open) 2. Physically restore (or copy) the datafile to its new location eg: /newlocation/myfile.dbf 3. Tell Oracle the new location of the file. eg: ALTER DATABASE RENAME FILE '/oldlocation/myfile.dbf' TO '/newlocation/myfile.dbf'; (Note that you cannot RENAME a TEMPFILE - TEMPFILEs should be dropped and recreated at the new location) 4. Online the relevant file / tablespace (if database is open) IMPORTANT: If there are multiple errors (which are NOT due to NOLOGGING) OR You have OS level errors against the affected file OR The errors are transient and keep moving about then there is little point proceeding until the underlying problem has been addressed or space is available on alternative disks. Get your hardware vendor to check the system over and contact Oracle Support with details of all errors. Please note: Whilst a failed hardware check is a good indication that there is a hardware issue, a successful hardware check should not be taken as proof that there is no hardware related issue - it is very common for hardware tests to report success when there really is some underlying fault. If using any special IO options such as direct IO , async IO or similar it may be worth disabling them in order to eliminate such options as a potential source of problems.

(3) Which Objects are Affected ?

It is best to determine which objects are affected BEFORE making any decisions about how to recover - this is because the corruption/s may be on object/s which can easily be re-created. Eg: For a corruption on a 5 row lookup table it may be far quicker to drop and recreate the table than to perform. a recovery. For each corruption collect the information in the following table. The steps to do this are explained below.
  • Information to Record for each Corruption
    Original
    Error
    Absolute
    File#
    &AFN
    Relative
    File#
    &RFN
    Block#

    &BL
    Tablespace Segment
    Type
    Segment
    Owner.Name
    Related
    Objects
    Recovery
    Options


















  The notes below will help you fill in this table for each corruption.

 "Original Error"
  This is the error as initially reported. 
  Eg: ORA-1578 / ORA-1110 , ORA-600 with all arguments etc..
 
 "Absolute File#", "Relative File#" and "Block#"
  The File# and Block# should have been given to you either by the
  error, by Oracle Support, or by the steps in an error article which
  directed you to this article. 

  In Oracle8/8i/9i/10g:  
		The absolute and relative file numbers are often the
               same but can differ (especially if the database has 
	       been migrated from Oracle7). It is important to get 
	       the correct numbers for &AFN and &RFN
               or you may end up salvaging the wrong object !!

	       An ORA-1578 reports the RELATIVE file number, with the
               ABSOLUTE file number given in the accompanying ORA-1110
               error. For ORA-600 errors you should be told an absolute
	       file number.

	       The following query will show the absolute and relative
	       file numbers for datafiles in the database:

                SELECT tablespace_name, file_id "AFN", relative_fno "RFN"
		  FROM dba_data_files;

  In Oracle8i/9i/10g: 
	       In addition to the notes above about Oracle8, Oracle8i onwards
	       can have TEMPFILES.  The following query will show the 
	       absolute and relative file numbers for tempfiles in the 
	       database:

		SELECT tablespace_name, file_id+value "AFN", relative_fno "RFN"
		  FROM dba_temp_files, v$parameter
		 WHERE name='db_files';

  In Oracle7:  Use the same file number for both the "Absolute File#"
               and the "Relative File#"


 
 "Segment Type", "Owner", "Name" and "Tablespace"
  The following query will tell you the object TYPE , OWNER and NAME of
  a segment given the absolute file number "&AFN" and block number "&BL" of the
  corrupt block - the database must be open in order to use this query:

        SELECT tablespace_name, segment_type, owner, segment_name
          FROM dba_extents
         WHERE file_id = &AFN
           and &BL between block_id AND block_id + blocks - 1
         ;

  If the block is in a TEMPFILE the above query will return no data.
  For TEMPFILES the "Segment Type" will be "TEMPORARY".

  If the above query does not return rows, it can also be that the corrupted block is a segment header
  in a Locally Managed Tablespace (LMT).  When the corrupted block is a segment 
  header block in a LMT,  the above query produces a corruption message in the alert.log 
  but the query does not not fail.  In that case use this query:

       SELECT owner, segment_name, segment_type, partition_name 
         FROM dba_segments
        WHERE header_file = &AFN
          and header_block = &BL
        ;
   
   Reference Note 819533.1

 
 "Related Objects" and Possible "Recovery Options" by SEGMENT_TYPE:
  The related objects and recovery options which can be used depend on the
  SEGMENT_TYPE. The additional queries and possible recovery options are 
  listed below for each of the most common segment types. 

	CACHE		
	CLUSTER 	
	INDEX PARTITION 	INDEX 		
	LOBINDEX 		LOBSEGMENT
	ROLLBACK 	        
        TABLE PARTITION		TABLE
	TEMPORARY 	
	TYPE2 UNDO 	
  	Some other Segment Type
	"no rows" from the query

  CACHE
	- If the segment type is CACHE recheck you have entered the SQL 
          and parameters correctly.
	  If you get the same result contact Oracle support with all 
	  information you have. 

	Options:
   	  The database is likely to require recovery.

	{Continue}  {Back to Segment List}

  CLUSTER	
	- If the segment is a CLUSTER determine which tables it contains.
	  Eg: 
		SELECT owner, table_name 
		  FROM dba_tables 
		 WHERE wner='&OWNER'
		   AND cluster_name='&SEGMENT_NAME' 
		;

	Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary clusters possible options include:
		Recovery
	    OR  Salvage data from all tables in the cluster
	   	THEN Recreate the cluster and all its tables
		
	  As the cluster may contain a number of tables, it is best to
	  collect information for each table in the cluster before making a
          decision. 

	{Collect TABLE information}  {Back to Segment List}

  INDEX PARTITION
 	- If the segment is an INDEX PARTITION note the NAME and OWNER 
	  and then determine which partition is affected thus:

		SELECT partition_name 
       		  FROM dba_extents
         	 WHERE file_id = &AFN
           	   AND &BL BETWEEN block_id AND block_id + blocks - 1
		;

	  then continue below as if the segment was an INDEX segment.

	Options:
	  Index partitions can be rebuilt using:
	    ALTER INDEX xxx REBUILD PARTITION ppp;    
	  (take care with the REBUILD option as described in
	    "Recreating Indexes" below)

		
  INDEX 
	- If the segment is an INDEX then if the OWNER is "SYS" contact 
	  Oracle support with all details.

          For a non-dictionary INDEX or INDEX PARTITIONs find out which table 
	  the INDEX is on:
	  Eg: 
	   	SELECT table_owner, table_name
		  FROM dba_indexes 
		 WHERE wner='&OWNER'
	    	   AND index_name='&SEGMENT_NAME'
		;

	  and determine if the index supports a CONSTRAINT:

	  Eg: 	SELECT owner, constraint_name, constraint_type, table_name 
		  FROM dba_constraints
		 WHERE wner='&TABLE_OWNER' 
		   AND constraint_name='&INDEX_NAME'
		;

	  Possible values for CONSTRAINT_TYPE are:

		P	The index supports a primary key constraint.
		U	The index supports a unique constraint.


	  If the INDEX supports a PRIMARY KEY constraint (type "P") then
	  check if the primary key is referenced by any foreign key constraints:
	  Eg: 
		SELECT owner, constraint_name, constraint_type, table_name 
		  FROM dba_constraints
		 WHERE r_owner='&TABLE_OWNER' 
		   AND r_constraint_name='&INDEX_NAME'
		;

	Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary indexes possible options include:
		Recovery
	    OR  Recreate the index (with any associated constraint
		  disables/enables)
		(take care with the REBUILD option as described in
		 "Recreating Indexes" below)

	{Continue}  {Back to Segment List}

  ROLLBACK
	- If the segment is a ROLLBACK segment contact Oracle support as
	  rollback segment corruptions require special handling. 

	Options:
	  The database is likely to require recovery.

	{Continue}  {Back to Segment List}

  TYPE2 UNDO
	- TYPE2 UNDO is a system managed undo segment which is a special
	  form. of rollback segment. Corruptions in these segments require
	  special handling.

	Options:
	  The database is likely to require recovery.

	{Continue}  {Back to Segment List}

  TABLE PARTITION	
 	- If the segment is a TABLE PARTITION note the NAME and OWNER 
	  and then determine which partition is affected thus:

		SELECT partition_name 
       		  FROM dba_extents
         	 WHERE file_id = &AFN
           	   AND &BL BETWEEN block_id AND block_id + blocks - 1
		;

	  then continue below as if the segment was a TABLE segment.

	Options:
	  If all corruptions are in the same partition then one option
	  at this point is to EXCHANGE the corrupt partition with an
	  empty TABLE - this can allow the application to continue (without
	  access to the data in the corrupt partition) whilst any good 
	  data can then be extracted from the table.

	  For other options see the TABLE options below.
	

  TABLE	
	- If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

          For a non-dictionary TABLE or TABLE PARTITIONs find out which 
	  INDEXES exist on the TABLE:
	  Eg: 
	   	SELECT owner, index_name, index_type
		  FROM dba_indexes 
		 WHERE table_owner='&OWNER'
	    	   AND table_name='&SEGMENT_NAME'
		;

	  and determine if there is any PRIMARY key on the table:

	  Eg: 	SELECT owner, constraint_name, constraint_type, table_name 
		  FROM dba_constraints
		 WHERE wner='&OWNER' 
		   AND table_name='&SEGMENT_NAME'
		   AND constraint_type='P'
		;

	  If there is a primary key then check if this is referenced by any 
	  foreign key constraints:
	  Eg: 
		SELECT owner, constraint_name, constraint_type, table_name 
		  FROM dba_constraints
		 WHERE r_owner='&OWNER' 
		   AND r_constraint_name='&CONSTRAINT_NAME'
		;

	Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary tables possible options include:
		Recovery
	    OR  Salvage data from the table (or partition)
	   	THEN Recreate the table (or partition)
	    OR  Leave the corruption in place
		(eg: Use DBMS_REPAIR to mark the problem blocks to be skipped)

	{Continue}  {Back to Segment List}


  IOT (Index Organized Table)
         The corruption in IOT table should be handled in the same way as in a heap or partitioned table.
         The only exception is if the PK is corrupted.
         PK of an IOT table is the table itself and can't be dropped and recreated.

        Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary tables possible options include:
		Recovery
	    OR  Salvage data from the table (or partition)
	   	THEN Recreate the table (or partition)
	    OR  Leave the corruption in place
		(DBMS_REPAIR cannot be used with IOTs)

{Continue}  {Back to Segment List}

  LOBINDEX	
        - Find out which table the LOB belongs to:

	 	SELECT table_name, column_name 
		  FROM dba_lobs 
		 WHERE wner='&OWNER'
		   AND index_name='&SEGMENT_NAME';

	- If the table is owned by "SYS" then contact Oracle support with all 
	  details.  The database is likely to require recovery.

	- It is not possible to rebuild LOB indexes and so you have to
	  treat the problem as a corruption on the LOB column of the
	  affected table.

	  Get index and constraint information for the table which has
	  the corrupt LOB index using the SQL in the TABLE
	  section, then return here.

	Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary tables possible options include:
		Recovery
	    OR  Salvage data from the table (and its LOB column/s)
	   	THEN Recreate the table 
	  It is not generally sensible just to leave the corruption in 
	  place unless the table is unlikely to have any further DML on 
	  the problem column.


	{Continue}  {Back to Segment List}
	

  LOBSEGMENT	

        - Find out which table the LOB belongs to:
	  Eg: 
	 	SELECT table_name, column_name 
		  FROM dba_lobs 
		 WHERE wner='&OWNER'
		   AND segment_name='&SEGMENT_NAME';

	- If the table is owned by "SYS" then contact Oracle support with all 
	  details.  The database is likely to require recovery.

	- For non-dictionary tables ...

	  Get index and constraint information for the table which has
	  the corrupt LOB data using the SQL in the TABLE
	  section, then return here to find details of the exact rows 
	  affected.

	  Finding the exact row which references the corrupt LOB block
	  can be a challenge as the errors reported do not show any
	  detail about which table row owns the lob entry which is corrupt.

	  Typically one can refer to application logs or any SQL_TRACE
	  or 10046 trace of a session hitting the error (if available) or
	  see if having event "1578 trace name errorstack level 3" 
	  set in the session helps identify the current SQL/binds/row.
	  eg:
		ALTER SYSTEM SET EVENTS '1578 trace name errorstack level 3';
		
		Then wait for the error to be hit by the application
		and find the trace file. 

	  If there are no clues then you can construct a PLSQL block
	  to scan the problem table row by row extracting the LOB
	  column data which loops until it hits an error. Such a technique
	  may take a while but it should be possible to get a primary key
	  or rowid of any row which references a corrupt LOB block.

	  eg: 
		set serverout on
		exec dbms_output.enable(100000);
		declare
		 error_1578 exception;
		 pragma exception_init(error_1578,-1578);
		 n number;
		 cnt number:=0;
		 badcnt number:=0;
		begin
		  for cursor_lob in
		        (select rowid r, &LOB_COLUMN_NAME L from &OWNER..&TABLE_NAME)
		  loop
		    begin
		      n:=dbms_lob.instr(cursor_lob.L,hextoraw('AA25889911'),1,999999) ;
		    exception
		     when error_1578 then
		       dbms_output.put_line('Got ORA-1578 reading LOB at '||cursor_lob.R);
		       badcnt:=badcnt+1;
		    end;
		    cnt:=cnt+1;
		  end loop;
		  dbms_output.put_line('Scanned '||cnt||' rows - saw '||badcnt||' errors');
		end;
		/


  	  It is possible to have a corrupt LOB block which is only 
	  present as an old version (for consistent read) and which has
	  not yet been re-used in which case all table rows will be
	  accessible but it may not be possible to insert / update
	  the LOB columns once that block is reclaimed for reuse.


	Options:
	  If the OWNER is "SYS" then contact Oracle support with all details.
   	  The database is likely to require recovery.

	  For non dictionary tables possible options include:
		Recovery
	    OR  Salvage data from the table (and its LOB column/s)
	   	THEN Recreate the table 
	    OR  Leave the corruption in place 
	  	(It is not possible to use DBMS_REPAIR on LOB segments)


	{Continue}  {Back to Segment List}

  TEMPORARY	
	- If the segment type is TEMPORARY then the corruption does not
	  affect a permanent object. Check if the tablespace where the
	  problem occurred is being used as a TEMPORARY tablespace thus:

		SELECT count(*) FROM dba_users
		 WHERE temporary_tablespace='&TABLESPACE_NAME'
		;

	Options:
	  If this is a TEMPORARY_TABLESPACE then it may be possible
	  to create a NEW temporary tablespace and switch all users
	  to that tablespace then DROP the problem tablespace.

	  If this is not a temporary tablespace then the block should
	  not be read again and should get re-formatted next time the
	  block is used - the error should not repeat PROVIDED any 
  	  underlying cause has been cured.

	  No restore is normally required, although if the disk is
	  suspect and the tablespace contains useful data then a 
	  database recovery of the affected file/s may be wise.


	{Continue}  {Back to Segment List}

  Some other SEGMENT_TYPE
	- If the segment type returned is not covered above then contact
	  Oracle support for advice with all information collected so far.

	{Continue}  {Back to Segment List}

  "no rows returned"
	- If there appears to be no extent containing the corrupt block
	  then first double check the figures used in the query. If you 
	  are sure the file and block are correct and do not appear as
	  belonging to an object in DBA_EXTENTS then:

		- Double check if the file involved is a TEMPFILE.
		  Note that TEMPFILE file numbers depend on the init.ora
		  parameter DB_FILES so any changes to this parameter
		  change the absolute file number reported in errors.

	        - DBA_EXTENTS does not include blocks which are used
		  for local space management in locally managed tablespaces.

		- If the database you are now querying is from a different
		  point in time to the datafile with the error then the
		  problem object may have been dropped and so queries against
		  DBA_EXTENTS may show no rows.

		- If the error you are investigating was reported by DBVERIFY
		  then DBV checks all blocks regardless of whether they 
		  belong to an object or not. This it is possible for a
	  	  corrupt block to exist in the datafile but in a block
		  not in use by any object.

	Options:
	  An error on an UNUSED Oracle block can be ignored as Oracle will
	  create a new block image should the block need to be used so any
	  existing problem on the block will never get read.

	  If you suspect that the block may be a space management
	  block then you can use DBMS_SPACE_ADMIN to help check
	  this by running:
			
	    exec DBMS_SPACE_ADMIN.TABLESPACE_VERIFY('&TABLESPACE_NAME');

	  This should write inconsistencies to the trace file but
	  if it encounters a fatally corrupt block it will report an
	  error like:
	    ORA-03216: Tablespace/Segment Verification cannot proceed
        
	  An error on a bitmap space management block can often be corrected
	  by running:

	   exec DBMS_SPACE_ADMIN.TABLESPACE_REBUILD_BITMAPS('&TABLESPACE_NAME');

	{Continue}  {Back to Segment List}

  Evidence>> 	
  	- For each corrupt block it is also a good idea to collect 
	  the following physical evidence if there is a need to try 
	  and identify the actual cause of the corruption:

	  i)  An operating system HEX dump of the bad block and the block 
	      either side of it.
	      On UNIX:  
	        dd if=&FILENAME bs=&TS_BLOCK_SIZE skip=&BL-1 count=3 f=BL.dd
		       ^^^^^^^^      ^^^^^^^^^^^^^^         ^^^
	      Eg: For BL=1224:
	        dd if=ts11.dbf bs=4k skip=1223 count=3 f=1223_1225.dd 

	      On VMS:    
		DUMP/BLOCKS=(start:XXXX,end:YYYY)/out=dump.out &FILENAME

		Where XXXX=Operating system block number (in 512 byte chunks)
		To calculate this multiply the block number reported by
		'&TS_BLOCK_SIZE/512'. 

	  ii) If you are in ARCHIVELOG mode make a safe copy of the archived 
	      log files around the time of the error, and preferably for a few 
	      hours before the error was reported. Also secure any backup/s
	      of the problem datafile from before the errors as the before
	      image PLUS redo can help point towards a cause.
	      (DBV can often be used to check if the problem exists in a
	       backup copy of a file). The ideal scenario is to have a 
	      datafile backup image which does not have any corruption
	      and all the redo from that point in time up to and just past
	      the time when the corruption is first reported.

	  iii) Obtain an Oracle dump of the problem block/s:

		ALTER SYSTEM DUMP DATAFILE '&FILENAME' 
		  BLOCK &BL
		;

	      (The output will go to a tracefile in the USER_DUMP_DEST).

	{Continue}  {Back to Segment List}

(4) Choosing a Recovery Option

The best recovery option now depends on the objects affected. The notes in Section (3) above should have highlighted the main options available for each affected object. The actual recovery method chosen may include a mix or one or more methods thus: Is any Recovery Required ? If the error is in a TEMPORARY tablespace, or is in a block which is no longer part of any database object then no action is required, although it may be wise to relocate the problem tablespace to a different storage device. See Warnings. Is Complete Recovery an option ? In order for complete recovery to be an option the following must be true: - The database is in ARCHIVELOG mode (The "ARCHIVE LOG LIST" command shows Archivelog Mode) - You have a good backup of affected files. Note that in some cases, the corruption may have been present, but undetected, for a long period of time. If the most recent datafile backup still contains the corruption, you can try an earlier backup as long as you have all the necessary ARCHIVELOGS. (You can often use the DBV START= / END= options to check if specific block/s in a restored copy of a backup file are corrupt) - All ARCHIVELOGS are available from the time of the backup to the current point in time - The current online log/s are available and intact - The errors are NOT due to recovery through a NOLOGGING operation When the above criteria are satisfied then complete recovery is usually the preferred option *BUT NOTE* (a) If the rollback of a transaction has seen a corrupt block on an object other than the rollback segment itself then UNDO may have been discarded. In this case you may need to rebuild indexes / check data integrity AFTER the recovery completes. (b) If the files to be recovered contain data from NOLOGGING operations performed since the last backup then those blocks will be marked corrupt if datafile or database recovery is used. In some cases this can put you in a worse scenario than the current position. If database recovery has already been performed and the corruption is still there then either all of your backups contain the corruption, the underlying fault is still present or the problem is replaying through redo. In these cases you will need to choose some other recovery option. See "(4A) Complete Recovery" for complete recovery steps. Can the object be Dropped or Re-created without needing to extract any data from the object itself ? It may be possible to lose the object, or to recreate it from a script. / recent export. Once an object is dropped then blocks in that object are marked as "free" and will be re-formatted when the block gets allocated to a new object. It is advisable to RENAME rather than DROP a table unless you are absolutely sure that you do not need any data in it. In the case of a table partition then only the affected partition needs to be dropped. eg: ALTER TABLE ... DROP PARTITION ... If the corruption affects the partition segment header, or the file containing the partition header is offline, then DROP PARTITION may fail. In this case it may still be possible to drop the partition by first exchanging it with a table of the same definition. eg: ALTER TABLE .. EXCHANGE PARTITION .. WITH TABLE ..; The most common object which can be re-created is an index. Always address TABLE corruptions before INDEX problems on a table. See "(4B) Recreating Indexes" for more details. For any segment, a quick way to extract the DDL for an object, when you have the absolute file number and block number of the corrupt block, is: set long 64000 select dbms_metadata.get_ddl(segment_type, segment_name, owner) FROM dba_extents WHERE file_id=&AFN AND &BL BETWEEN block_id AND block_id + blocks -1; Is it required to salvage data before recreating the object ? If the problem is on a critical application table which is regularly updated then it may be required to salvage as much data from the table as possible, then recreate the table. See "(4C) Salvaging Data from Tables" for more details. Is it acceptable to leave the corruption in place for the moment? In some cases the best immediate option may be to leave the corruption in place and isolate it from application access. See "(4D) Leaving the Corruption In Place" for more details. Last Options Are any of the following possible ? Recovery to an old point-in-time (via point in time recovery) of either the database or tablespace point in time recovery OR Restore of a COLD backup from before the corruption OR Use of an existing export file See "(4E) Last Options" for more details.

(4A) Complete Recovery

If the database is in ARCHIVELOG mode and you have a good backup of the affected files then recovery is usually the preferred option. This is not GUARANTEED to clear a problem, but is effective for the majority of corruption issues. If recovery re-introduces the problem then return to the list of options above and choose another method. If you are using Oracle9i (or higher) then it may be possible to perform. block level recovery using the RMAN BLOCKRECOVER command. If using an earlier Oracle release then you can either perform. datafile recovery (which can be done while the rest of the database is still up and running), or database recovery (which requires the database to be taken down) . If you are using Oracle 11g (or higher) then it may be possible to use Data Recovery Advisor (see Note 1317849.1) Block Level Recovery ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ As of Oracle9i RMAN allows individual blocks to be recovered whilst the rest of the database (including other blocks in the datafile) are available for normal access. Note that block level recovery can only be used to recover a block fully to the current point in time. It is not necessary to be using RMAN for backups to be able to use this option for recovery of individual blocks. eg: Consider that you have an ORA-1578 on file #6 block #30 which is likely due to a media corruption problem and there is a good cold backup image of that file which has been restored to '.../RESTORE/filename.dbf'. Provided all archivelogs exist (in the default location) then you can use RMAN to perform. a block level recovery using a command sequence like: rman nocatalog connect target catalog datafilecopy '.../RESTORE/filename.dbf'; run {blockrecover datafile 6 block 30;} This will use the registered datafile backup image and any required archivelogs to perform. block recovery of just the one problem block to current point in time. Please see the documentation for full details of the RMAN BLOCKRECOVER command and limitations. Datafile Recovery ~~~~~~~~~~~~~~~~~~ Datafile recovery of a file involves the following steps. If there are several files repeat the steps for each file or see "Database Recovery" below. These steps can be used if the database is either OPEN or MOUNTED. OFFLINE the affected data file eg: ALTER DATABASE DATAFILE 'name_of_file' OFFLINE; Copy it to a safe location (in case the backup is bad) Restore the latest backup of the file onto a GOOD disk Check the restored file for obvious corruptions with DBVERIFY For details of using DBVERIFY see Note:35512.1 Assuming the restored file is OK, then RENAME the datafile to the NEW location (if different from the old location) eg: ALTER DATABASE RENAME FILE 'old_name' TO 'new_name'; Recover the datafile eg: RECOVER DATAFILE 'name_of_file'; Online the file/s eg: ALTER DATABASE DATAFILE 'name_of_file' ONLINE; {Continue} Database Recovery ~~~~~~~~~~~~~~~~~ Database recovery generally involves the following steps: Shutdown (Immediate or Abort) Copy the current copy of all files to be recovered to a safe location Restore the backup files to a GOOD disk location DO NOT RESTORE THE CONTROL FILES or ONLINE REDO LOG FILES Check restored files with DBVERIFY For details of using DBVERIFY see Note:35512.1 Startup MOUNT Rename any relocated files eg: ALTER DATABASE RENAME FILE 'old_name' TO 'new_name'; Ensure all required files are online eg: ALTER DATABASE DATAFILE 'name_of_file' ONLINE; Recover the database eg: RECOVER DATABASE Open the database eg: ALTER DATABASE OPEN; After a Complete Recovery ~~~~~~~~~~~~~~~~~~~~~~~~~~ Once a complete recovery has been performed it is advisable to check the database before allowing it to be used: - Run "ANALYZE VALIDATE STRUCTURE CASCADE" against each problem object to check for table/index mis-matches. If there has been any UNDO discarded this may show a mismatch requiring indexes to be re-created. - Check the logical integrity of data in the table at the application level.

(4B) Recreating Indexes

If the corrupt object is a user INDEX you can simply drop and re-create it PROVIDED the underlying table is not also corrupt. If the underlying table is also corrupt it is advisable to sort out the TABLE before recreating any indexes. If the information collected shows that the index has dependent FOREIGN KEY constraints then you will need to do something like this: - ALTER TABLE DISABLE CONSTRAINT ; for each foreign key - Rebuild the primary key using ALTER TABLE DISABLE CONSTRAINT ; DROP INDEX ; CREATE INDEX .. with appropriate storage clause ALTER TABLE
ENABLE CONSTRAINT ; - Enable the foreign key constraints ALTER TABLE ENABLE CONSTRAINT ; For an index partition you can: ALTER INDEX ... REBUILD PARTITION ...; Notes: (1) It is important not to REBUILD a non-partitioned corrupt index using an "ALTER INDEX .. REBUILD" command as this will usually try to build the new index from the existing index segment, which contains a corrupt block. "ALTER INDEX ... REBUILD ONLINE" and "ALTER INDEX ... REBUILD PARTITION ..." do not build the new index from the old index segment and so can be used. (2) Create INDEX can use the data from an existing index if the new index is a sub-set of the columns in the existing index. Hence if you have 2 corrupt indexes drop them BOTH before re-creating them. (3) Be sure to use the correct storage details when recreating indexes.

(4C) Salvaging Data from Tables

If the corrupt object is a TABLE or CLUSTER or LOBSEGMENT then it must be understood that the data within the corrupt block is lost. Some of the data may be salvageable from a HEX dump of the block, or from columns covered by indexes. Important: As it may be required to salvage data in the corrupt block from the indexes it is a good idea NOT to drop any existing index until any required data has been extracted. There are many ways to get data out of a table which contains a corrupt block. Choose the most appropriate method as detailed below. The aim of these methods is to extract as much data as possible from the table blocks which can be accessed. It is usually a good idea to RENAME the corrupt table so that the new object can be created with the correct name. Eg: RENAME TO ; Methods of extracting data from a corrupt table AROUND a corrupt block (1) From Oracle 7.2 onwards, including Oracle 8.0, 8.1, and 9i, it is possible to SKIP over corrupt blocks in a table. This is by far the simplest option to extract table data and is discussed in: Extracting data using DBMS_REPAIR.SKIP_CORRUPT_BLOCKS or Event 10231 Note:33405.1 If the corruption is in an IOT overflow segment then the same method should be followed, but using event 10233 together with a full index scan. Note that this method can only be used if the block "wrapper" is marked corrupt. Eg: If the block reports ORA-1578. If the problem is an ORA-600 or other error which does not report and ORA-1578 error then it is often possible to use DBMS_REPAIR to mark the problem blocks in a table as "soft corrupt" such that they will then signal ORA-1578 when accessed which then allows you to use DBMS_REPAIR.SKIP_CORRUPT_BLOCKS. Note: Any blocks which are marked corrupt by the "FIX_CORRUPT_BLOCKS" procedure will also be marked corrupt following any restore / recover operation through the time of the FIX_CORRUPT_BLOCKS. Full details of using DBMS_REPAIR for this can be found in the documentation but in summary the steps are: - Use DBMS_REPAIR.ADMIN_TABLES to create the admin tables - Use DBMS_REPAIR.CHECK_OBJECT to find problem blocks - Get any good data out of problem blocks before corrupting them. - Use DBMS_REPAIR.FIX_CORRUPT_BLOCKS to mark the found problem blocks as corrupt so that they will then signal ORA-1578 - If required use DBMS_REPAIR.SKIP_CORRUPT_BLOCKS to skip corrupt blocks on the table. (2) From Oracle 7.1 onwards you can use a ROWID range scan. The syntax for this is a little tricky but it is possible to select around a corrupt block using a ROWID hint. As the format of ROWIDs changed between Oracle7 and Oracle8 there are 2 articles which discuss this: Using ROWID Range Scans to extract data in Oracle8 and higher Note:61685.1 Using ROWID Range Scans to extract data in Oracle7 Note:34371.1 (3) If there is a primary key you can select table data via this index. It may also be possible to select some of data via any other index. This can be slow and time consuming and is only normally needed for Oracle 7.0 releases. This method is described in Note:34371.1 (which also describes the ROWID range scans) (4) There are various salvage programs / PLSQL scripts which can be used to salvage data from a table. These can take longer to set up and use than the above methods but can often cope with various kinds of corruption besides an ORA-1578. As these methods typically require much hand-holding from support then some of these articles may not be visible to customers.These require Pro*C to be available and an understanding of how to build Pro*C executables: SALVAGE.PC for Oracle7 Note:2077307.6These requires manual interaction: SALVAGE.SQL for Oracle7/8 Note:2064553.4Methods of extracting data from a table with a corrupt LOBSEGMENT block It is not possible to used DBMS_REPAIR on LOB segments. If the corrupt LOB block is NOT referenced by any row in the table then it should be possible to CREATE TABLE as SELECT (CTAS) or export / drop / import the table as is. If the corrupt LOB block is referenced by a row then it should be possible to select or export with a WHERE predicate that excludes the problem row/s. WARNING: It is possible to update the LOB column value of a problem row to NULL which will then clear ORA-1578 on SELECT operations *BUT* the corrupt block will then be waiting to be reclaimed and will eventually signal an ORA-1578 on attempts to get a new LOB for INSERT or UPDATE operations on any row which can be a worse situation than having a corruption on a known row. Hence you should only really set the LOB column to NULL if you intend to immediately recreate the table. Extracting data from the corrupt block itself As the corrupt block itself is "corrupt" then any data extracted from the block should be treated as suspect. The main methods of getting the rows from the corrupt block itself are: - For TABLE blocks Oracle Support can use a tool which attempts to interpret the block contents. - Use any existing indexes on the table to extract data for columns covered by the index where the ROWID falls inside the corrupt block. This is described towards the end of the ROWID range scan articles mentioned above: For Oracle8/8i see Note:61685.1 For Oracle7 see Note:34371.1 - It may be possible to use LogMiner on the redo stream to find the original inserts/updates which loaded the data to the problem block. The main factor here is WHEN the data was actually put in the block. eg; row 2 may have been inserted yesterday but row 1 may have been inserted 5 years ago.

(4D) Leaving A Corruption In Place

It is possible to leave a corruption in place and just accept the errors reported, or prevent access to the problem rows at an application level. eg: If the problem block / row is in a child table then it may be possible at application level to prevent access via the parent row/s such that the child rows are never accessed. (Be wary of cascade type constraints though) This may not help with reports and other jobs which access data in bulk so it may also be desirable to use the DBMS_REPAIR options shown in 4C above to prevent the block/s erroring when accessed. Marking a corruption like this and leaving it around may give a short term solution allowing full data salvage and/or recovery to be attempted at scheduled outage, or allowing time to check other recovery options on a second (clone) database. Note though that marking a block corrupt with DBMS_REPAIR.FIX_CORRUPT_BLOCKS will cause the marked block/s to also be corrupt after recovery through the time that FIX_CORRUPT_BLOCKS was executed. Leaving a corruption may be sensible for data which rapidly ages and is subsequently purged (eg: In a date partitioned table where older partitions are dropped at some point). Leaving Corruptions in LOB segments At application level it can be possible to leave a corrupt LOB column in place until such time as the table can be rebuilt. One way to ensure you do not hit the "WARNING" scenario above is to ensure that the table is only ever accessed via a view which includes a WHERE predicate to prevent the problem row/s from being seen. eg: Consider table MYTAB( a number primary key, b clob ) has one or more rows pointing at corrupt LOB data. ALTER TABLE MYTAB ADD ( BAD VARCHAR2(1) ); CREATE VIEW MYVIEW AS SELECT a,b FROM MYTAB WHERE BAD is null; Set BAD='Y' for any problem row/s If you only access MYTAB via MYVIEW and the row will never be visible and so cannot be updated keeping the corrupt entry isolated until it can be dealt with. Clearly this example is more of a design time solution but some applications may already have similar mechanisms and may only access data via a view (or via an RLS policy) giving some option/s to hide the problem row/s. Warnings when Leaving a Corruption in Place Whilst it is possible to leave a corruption in place it should be noted that the corrupt blocks will still show up in runs of DBVERIFY, in RMAN backup warnings / errors etc.. It is important to make a careful record of any corruption you expect to see from these tools, particularly any blocks you expect to skip with RMAN (eg: having MAX_CORRUPT set) and be sure to remove any "acceptance" of the errors once the corruptions have been cleared. eg: Consider that a corrupt block has been handled by leaving the corruption in place and avoiding the problem row/s at application level. RMAN may be configured to allow the corruptions during backup. The table is then recreated at a later date during some table reorganisation. If RMAN is not updated to reflect that no errors should now be expected then RMAN may ignore some other corruption which occurs at a later time. It is also important to note that leaving corrupt blocks around in table segments can lead to mismatched results from queries eg: different results can occur for tables with SKIP_CORRUPT set depending on whether an index scan or table access occurs. Other reports may just error . Note that leaving a corruption in place but marking the block with DBMS_REPAIR.FIX_CORRUPT_BLOCKS writes redo to corrupt the block which may limit subsequent recovery options.

(4E) Last Options

If you have a standby setup (physical or logical) then check that first. Whatever sort of block the problem occurred on, one possible option is to recover the database, or problem tablespace, to a point in time BEFORE the corruption appeared. The difficulty with this option is that it is not always possible to know when the problem first appeared. DBVERIFY can be often be used to check a restored file for corruptions. For details of using DBVERIFY see Note:35512.1 . In particular the START= / END= DBV options can be used to give a quick first test of whether the problem block itself is bad on a restored backup image. This section outlines some final options available for recovering. If you have come here then one or more of the following have happened: - You have lost a "vital" datafile (or have a corruption on it) and have no good backup of the problem file/s (without the corruption) - Are either not in ARCHIVELOG mode OR do not have all archivelogs since the file was first created - Complete recovery keeps reintroducing the problem Last chance: Please note if you have lost all copies of a datafile but DO still have the ARCHIVE logs from when the file was first created it is still possible to recover the file. Eg: ALTER DATABASE CREATE DATAFILE '....' [as '...'] ; RECOVER DATAFILE '....' ALTER DATABASE DATAFILE '....' ONLINE; If you are in this scenario try to recover the datafile using these steps before proceeding below. If you have reached this line there are no options left to recover to the current point in time. It is advisable to shutdown the instance and take a BACKUP of the current database NOW in order to provide a fall-back position if the chosen course of action fails. (Eg: if you find your backup is bad). Some outline options available are: Revert to an old COLD backup - eg: If in NOARCHIVELOG mode Set up a clone database from a COLD backup - and extract (export) the problem table/s or transport the problem tablespace Point in time recovery to an older point in time that is consistent - requires a good backup and any necessary archive logs - ALL files have to be restored and the whole DB rolled forward to a suitable point in time. - It may be possible to do the point in time recovery in a clone database and then transport the problem tablespace to the problem database, or export / import the problem table from the clone to the problem database . Tablespace point in time recovery - It may be possible to perform. a point in time recovery of the affected tablespace only. There are many notes describing tablespace point in time recovery such as Note:223543.1. Rebuild of DB from some logical export / copy - Requires there to already be a good logical backup of the database - NB: You have to RE-CREATE the database for this option. - As with other options the rebuild could be in a clone database just to get a good image of the problem table/s. If you have a good backup then rolling forwards with DB_BLOCK_CHECKING=TRUE can help find the first point in time where something started to go wrong. It is not generally necessary to take the problem database down while investigating the recovery options. eg: You can restore the system tablespace and problem tablespace datafiles only to a totally different location and/or machine as a different instance to investigate how far you can roll forwards etc.. As of Oracle9i you can also use "Trial Recovery" options to save having to keep restoring a backup while looking into your options.
Document History 29-APR-2011 Add reference to Note 1317849.1 18-Aug-2009 Add reference to Note 869305.1 15-Oct-2008 Minor addition of script. to get_ddl 24-Feb-2006 Major additions for LOBs, BLOCKRECOVER, TSPITR, further DBMS_REPAIR options 03-Mar-2005 Minor change to "dd" command to use 22-Nov-2001 Include 9i and multiple block sizes 13-Sep-2001 Add TEMPFILE details 12-Sep-2000 Major rewrite / merge

References

NOTE:1088018.1 - Master Note for Handling Oracle Database Corruption Issues
NOTE:1317849.1 - Data Recovery Advisor - Corruption Reference Guide

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