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

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

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  수정 날짜 11-JUL-2012     유형 BULLETIN     상태 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 owner='&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 owner='&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 owner='&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 owner='&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 owner='&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 owner='&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 of=BL.dd
         ^^^^^^^^      ^^^^^^^^^^^^^^         ^^^
       Eg: For BL=1224:
         dd if=ts11.dbf bs=4k skip=1223 count=3 of=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 <table_name> 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 <child_table> DISABLE CONSTRAINT <fk_constraint>;
   for each foreign key

 - Rebuild the primary key using
     ALTER TABLE <table> DISABLE CONSTRAINT <pk_constraint>;
     DROP INDEX <index_name>;
     CREATE INDEX <index_name> .. with appropriate storage clause
     ALTER TABLE <table> ENABLE CONSTRAINT <pk_constraint>;

 - Enable the foreign key constraints
     ALTER TABLE <child_table> ENABLE CONSTRAINT <fk_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 <emp> TO <emp_corrupt>;

  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:2077307.6

   These requires manual interaction:
     SALVAGE.SQL for Oracle7/8    Note:2064553.4

 

  Methods 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

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

    
    
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