ORACLE DBA

Thursday, August 14, 2014

Non critical error ORA-48913 caught while writing to trace file "/oracle/saptrace/diag/rdbms/XXX/trace/XXX_lgwr_36503556.trc" Error message: ORA-48913: Writing into trace file failed, file size limit [10240000] reached End of report

Oracle 11g Recommendations are below.

SQL> show parameter max_dump_file

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
max_dump_file_size string 20000
SQL> alter system set max_dump_file_size=UNLIMITED scope=both;

System altered.

SQL> show parameter max_dump_file

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
max_dump_file_size string UNLIMITED

Wednesday, August 13, 2014

Statistics In Oracle

In this post I'll try to summarize all sorts of statistics in Oracle, I strongly recommend reading the full article, as it contains information you may find it valuable in understanding Oracle statistics.

################################

Database | Schema | Table | Index Statistics

################################

Gather Database Stats:

===================

SQL> EXEC DBMS_STATS.GATHER_DATABASE_STATS(

ESTIMATE_PERCENT=>100,METHOD_OPT=>'FOR ALL COLUMNS SIZE SKEWONLY',

CASCADE => TRUE,

degree => 4,

OPTIONS => 'GATHER STALE',

GATHER_SYS => TRUE,

STATTAB => PROD_STATS);

CASCADE => TRUE :Gather statistics on the indexes as well. If not used Oracle will determine whether to collected or not.

DEGREE => 4 :Degree of parallelism.

options:

=>'GATHER' :Gathers statistics on all objects in the schema.

=>'GATHER AUTO' :Oracle determines which objects need new statistics, and determines how to gather those statistics.

=>'GATHER STALE':Gathers statistics on stale objects. will return a list of stale objects.

=>'GATHER EMPTY':Gathers statistics on objects have no statistics.will return a list of no stats objects.

=>'LIST AUTO' : Returns a list of objects to be processed with GATHER AUTO.

=>'LIST STALE': Returns a list of stale objects as determined by looking at the *_tab_modifications views.

=>'LIST EMPTY': Returns a list of objects which currently have no statistics.

GATHER_SYS => TRUE :Gathers statistics on the objects owned by the 'SYS' user.

STATTAB => PROD_STATS :Table will save the current statistics. see SAVE & IMPORT STATISTICS section -last third in this post-.

Note: All above parameters are valid for all stats kind (schema,table,..) except Gather_SYS.

For faster execution:

------------------

SQL> EXEC DBMS_STATS.GATHER_DATABASE_STATS(

ESTIMATE_PERCENT=>DBMS_STATS.AUTO_SAMPLE_SIZE,degree => 8);

What's new?

ESTIMATE_PERCENT=>DBMS_STATS.AUTO_SAMPLE_SIZE => Let Oracle estimate skewed values always gives excellent results.(DEFAULT).

Removed "METHOD_OPT=>'FOR ALL COLUMNS SIZE SKEWONLY'" => As histograms is not recommended to be gathered on all columns.

Removed "cascade => TRUE" To let Oracle determine whether index statistics to be collected or not.

Doubled the "degree => 8" but this depends on the number of CPUs on the machine and accepted CPU overhead during gathering DB statistics.

This task became an automated task starting with 10g to gathers statistics on all objects in the database having stale or missing statistics, To check the status of that task:

SQL> select status from dba_autotask_client where client_name = 'auto optimizer stats collection';

To Enable automatic optimizer statistics task:

SQL> BEGIN

DBMS_AUTO_TASK_ADMIN.ENABLE(

client_name => 'auto optimizer stats collection',

operation => NULL,

window_name => NULL);

END;

In case you want to Disable automatic optimizer statistics task:

SQL> BEGIN

DBMS_AUTO_TASK_ADMIN.DISABLE(

client_name => 'auto optimizer stats collection',

operation => NULL,

window_name => NULL);

END;

To check the tables that have stale statistics:

SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES';

Gather SCHEMA Stats:

=====================

SQL> Exec DBMS_STATS.GATHER_SCHEMA_STATS (

ownname =>'SCOTT',

estimate_percent=>10,

degree=>1,

cascade=>TRUE,

options=>'GATHER STALE');

Gather TABLE Stats:

===================

Check table statistics date:

SQL> select table_name, last_analyzed from user_tables where table_name='T1';

SQL> Begin DBMS_STATS.GATHER_TABLE_STATS (

ownname => 'SCOTT',

tabname => 'EMP',

degree => 2,

cascade => TRUE,

METHOD_OPT => 'FOR COLUMNS SIZE AUTO',

estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE);

END;

CASCADE => TRUE : Gather statistics on the indexes as well. If not used Oracle will determine whether to collect it or not.

DEGREE => 2: Degree of parallelism.

ESTIMATE_PERCENT => DBMS_STATS.AUTO_SAMPLE_SIZE : (DEFAULT) Auto set the sample size % for skew(distinct) values (accurate and faster than setting a manual sample size).

METHOD_OPT=> : For gathering Histograms:

FOR COLUMNS SIZE AUTO : You can specify one column between "" instead of all columns.

FOR ALL COLUMNS SIZE REPEAT : Prevent deletion of histograms and collect it only for columns already have histograms.

FOR ALL COLUMNS : Collect histograms on all columns.

FOR ALL COLUMNS SIZE SKEWONLY : Collect histograms for columns have skewed value should test skewness first>.

FOR ALL INDEXED COLUMNS : Collect histograms for columns have indexes only.

Note: Truncating a table will not update table statistics, it will only reset the High Water Mark, you've to re-gather statistics on that table.

Inside "DBA BUNDLE", there is a script called "gather_stats.sh", it will help you easily & safely gather statistics on specific schema or table plus providing advanced features such as backing up/ restore new statistics in case of fallback.

To learn more about "DBA BUNDLE" please visit this post:

http://dba-tips.blogspot.com/2014/02/oracle-database-administration-scripts.html

Gather Index Stats:

==================

SQL> exec DBMS_STATS.GATHER_INDEX_STATS(ownname => 'SCOTT',indname => 'EMP_I',

estimate_percent =>DBMS_STATS.AUTO_SAMPLE_SIZE);

###################

Fixed OBJECTS Statistics

###################

What are Fixed objects:

---------------------

-Fixed objects are the x$ tables (been loaded in SGA during startup) on which V$ views are built (V$SQL etc.).

-If the statistics are not gathered on fixed objects, the Optimizer will use predefined default values for the statistics. These defaults may lead to inaccurate execution plans.

-Statistics on fixed objects are not being gathered automatically nor within gathering DB stats.

How frequent to gather stats on fixed objects?

------------------------------------------

Only one time for a representative workload unless you've one of these cases:

- After a major database or application upgrade.

- After implementing a new module.

- After changing the database configuration. e.g. changing the size of memory pools (sga,pga,..).

- Poor performance/Hang encountered while querying dynamic views e.g. V$ views.

Note:

- It's recommended to Gather the fixed object stats during peak hours (system is busy) or after the peak hours but the sessions are still connected (even if they idle), to guarantee that the fixed object tables been populated and the statistics well represent the DB activity.

- Also note that performance degradation may be experienced while the statistics are gathering.

- Having no statistics is better than having a non representative statistics.

How to gather stats on fixed objects:

----------------------------------

First Check the last analyzed date:

---- --------------------------

SQL> select OWNER, TABLE_NAME, LAST_ANALYZED

from dba_tab_statistics where table_name='X$KGLDP';

Second Export the current fixed stats in a table: (in case you need to revert back)

------- -----------------------------------

SQL> EXEC DBMS_STATS.CREATE_STAT_TABLE

('OWNER','STATS_TABLE_NAME','TABLESPACE_NAME');

SQL> EXEC dbms_stats.export_fixed_objects_stats

(stattab=>'STATS_TABLE_NAME',statown=>'OWNER');

Third Gather the fixed objects stats:

------ ------------------------

SQL> exec dbms_stats.gather_fixed_objects_stats;

Note:

In case you experienced a bad performance on fixed tables after gathering the new statistics:

SQL> exec dbms_stats.delete_fixed_objects_stats();

SQL> exec DBMS_STATS.import_fixed_objects_stats

(stattab =>'STATS_TABLE_NAME',STATOWN =>'OWNER');

#################

SYSTEM STATISTICS

#################

What is system statistics:

-----------------------

System statistics are statistics about CPU speed and IO performance, it enables the CBO to

effectively cost each operation in an execution plan. Introduced in Oracle 9i.

Why gathering system statistics:

------------------------------

Oracle highly recommends gathering system statistics during a representative workload,

ideally at peak workload time, in order to provide more accurate CPU/IO cost estimates to the optimizer.

You only have to gather system statistics once.

There are two types of system statistics (NOWORKLOAD statistics & WORKLOAD statistics):

NOWORKLOAD statistics:

--------------------------

This will simulates a workload -not the real one but a simulation- and will not collect full statistics, it's less accurate than "WORKLOAD statistics" but if you can't capture the statistics during a typical workload you can use noworkload statistics.

To gather noworkload statistics:

SQL> execute dbms_stats.gather_system_stats();

WORKLOAD statistics:

----------------------

This will gather statistics during the current workload [which supposed to be representative of actual system I/O and CPU workload on the DB].

To gather WORKLOAD statistics:

SQL> execute dbms_stats.gather_system_stats('start');

Once the workload window ends after 1,2,3.. hours or whatever, stop the system statistics gathering:

SQL> execute dbms_stats.gather_system_stats('stop');

You can use time interval (minutes) instead of issuing start/stop command manually:

SQL> execute dbms_stats.gather_system_stats('interval',60);

Check the system values collected:

-------------------------------

col pname format a20

col pval2 format a40

select * from sys.aux_stats$;

cpuspeedNW: Shows the noworkload CPU speed, (average number of CPU cycles per second).

ioseektim: The sum of seek time, latency time, and OS overhead time.

iotfrspeed: I/O transfer speed,tells optimizer how fast the DB can read data in a single read request.

cpuspeed: Stands for CPU speed during a workload statistics collection.

maxthr: The maximum I/O throughput.

slavethr: Average parallel slave I/O throughput.

sreadtim: The Single Block Read Time statistic shows the average time for a random single block read.

mreadtim: The average time (seconds) for a sequential multiblock read.

mbrc: The average multiblock read count in blocks.

Notes:

-When gathering NOWORKLOAD statistics it will gather (cpuspeedNW, ioseektim, iotfrspeed) system statistics only.

-Above values can be modified manually using DBMS_STATS.SET_SYSTEM_STATS procedure.

-According to Oracle, collecting workload statistics doesn't impose an additional overhead on your system.

Delete system statistics:

---------------------

SQL> execute dbms_stats.delete_system_stats();

####################

Data Dictionary Statistics

####################

Facts:

-----

> Dictionary tables are the tables owned by SYS and residing in the system tablespace.

> Normally data dictionary statistics in 9i is not required unless performance issues are detected.

> In 10g Statistics on the dictionary tables will be maintained via the automatic statistics gathering job run during the nightly maintenance window.

If you choose to switch off that job for application schema consider leaving it on for the dictionary tables. You can do this by changing the value of AUTOSTATS_TARGET from AUTO to ORACLE using the procedure:

SQL> Exec DBMS_STATS.SET_PARAM(AUTOSTATS_TARGET,'ORACLE');

When to gather Dictionary statistics:

---------------------------------

-After DB upgrades.

-After creation of a new big schema.

-Before and after big datapump operations.

Check last Dictionary statistics date:

----------------------------------

SQL> select table_name, last_analyzed from dba_tables

where owner='SYS' and table_name like '%$' order by 2;

Gather Dictionary Statistics:

-------------------------

SQL> EXEC DBMS_STATS.GATHER_DICTIONARY_STATS;

->Will gather stats on 20% of SYS schema tables.

or...

SQL> EXEC DBMS_STATS.GATHER_SCHEMA_STATS ('SYS');

->Will gather stats on 100% of SYS schema tables.

or...

SQL> EXEC DBMS_STATS.GATHER_DATABASE_STATS(gather_sys=>TRUE);

->Will gather stats on the whole DB+SYS schema.

#############

Extended Statistics "11g onwards"

#############

Extended statistics can be gathered on columns based on functions or column groups.

Gather extended stats on column function:

=====================================

If you run a query having in the WHERE statement a function like upper/lower the optimizer will be off and index on that column will not be used:

SQL> select count(*) from EMP where lower(ename) = 'scott';

In order to make optimizer work with function based terms you need to gather extended stats:

1-Create extended stats:

>>>>>>>>>>>>>>>>>>>>>

SQL> select dbms_stats.create_extended_stats('SCOTT','EMP','(lower(ENAME))') from dual;

2-Gather histograms:

>>>>>>>>>>>>>>>>>>

SQL> exec dbms_stats.gather_table_stats('SCOTT','EMP', method_opt=> 'for all columns size skewonly');

*You can do it also in one Step:

>>>>>>>>>>>>>>>>>>>>>>>>>

SQL> Begin dbms_stats.gather_table_stats

(ownname => 'SCOTT',tabname => 'EMP',

method_opt => 'for all columns size skewonly for

columns (lower(ENAME))');

end;

To check the Existance of extended statistics on a table:

---------------------------------------------------

SQL> select extension_name,extension from dba_stat_extensions where owner='SCOTT'and table_name = 'EMP';

SYS_STU2JLSDWQAFJHQST7$QK81_YB (LOWER("ENAME"))

Drop extended stats on column function:

-------------------------------------

SQL> exec dbms_stats.drop_extended_stats('SCOTT','EMP','(LOWER("ENAME"))');

Gather extended stats on column group: -related columns-

=================================

Certain columns in a table that are part of a join condition (where statement are correlated e.g.(country,state). You want to make the optimizer aware of this relationship between two columns and more instead of using separate statistics for each columns. By creating extended statistics on a group of columns, the Optimizer can determine a more accurate the relation between the columns are used together in a where clause of a SQL statement. e.g. columns like country_id and state_name the have a relationship, state like Texas can only be found in USA so the value of state_name are always influenced by country_id.

If there are extra columns are referenced in the "WHERE statement with the column group the optimizer will make use of column group statistics.

1- create a column group:

>>>>>>>>>>>>>>>>>>>>>

SQL> select dbms_stats.create_extended_stats('SH','CUSTOMERS', '(country_id,cust_state_province)')from dual;

2- Re-gather stats|histograms for table so optimizer can use the newly generated extended statistics:

>>>>>>>>>>>>>>>>>>>>>>>

SQL> exec dbms_stats.gather_table_stats ('SH','customers',method_opt=> 'for all columns size skewonly');

---

*You can do it also in one Step:

>>>>>>>>>>>>>>>>>>>>>>>>>

SQL> Begin dbms_stats.gather_table_stats

(ownname => 'SH',tabname => 'CUSTOMERS',

method_opt => 'for all columns size skewonly for

columns (country_id,cust_state_province)');

end;

Drop extended stats on column group:

--------------------------------------

SQL> exec dbms_stats.drop_extended_stats('SH','CUSTOMERS', '(country_id,cust_state_province)');

########

Histograms

########

What are Histograms?

-----------------------

> Holds data about values within a column in a table for number of occurrences for a specific value/range.

> Used by CBO to optimize a query to use whatever index Fast Full scan or table full scan.

> Usually being used against columns have data being repeated frequently like country or city column.

> gathering histograms on a column having distinct values (PK) is useless because values are not repeated.

> Two types of Histograms can be gathered:

-Frequency histograms: is when distinct values (buckets) in the column is less than 255 (e.g. the number of countries is always less than 254).

-Height balanced histograms: are similar to frequency histograms in their design, but distinct values > 254

See an Example: http://aseriesoftubes.com/articles/beauty-and-it/quick-guide-to-oracle-histograms

> Collected by DBMS_STATS (which by default doesn't collect histograms, it deletes them if you didn't use the parameter).

> Mainly being gathered on foreign key columns/columns in WHERE statement.

> Help in SQL multi-table joins.

> Column histograms like statistics are being stored in data dictionary.

> If application exclusively uses bind variables, Oracle recommends deleting any existing histograms and disabling Oracle histograms generation.

Cautions:

– Do not create them on Columns that are not being queried.

– Do not create them on every column of every table.

– Do not create them on the primary key column of a table.

Verify the existence of histograms:

--------------------------------------

SQL> select column_name,histogram from dba_tab_col_statistics

where owner='SCOTT' and table_name='EMP';

Creating Histograms:

-----------------------

e.g.

SQL> Exec dbms_stats.gather_schema_stats

(ownname => 'SCOTT',

estimate_percent => dbms_stats.auto_sample_size,

method_opt => 'for all columns size auto',

degree => 7);

method_opt:

FOR COLUMNS SIZE AUTO => Fastest. you can specify one column instead of all columns.

FOR ALL COLUMNS SIZE REPEAT => Prevent deletion of histograms and collect it only for columns already have histograms.

FOR ALL COLUMNS => collect histograms on all columns .

FOR ALL COLUMNS SIZE SKEWONLY => collect histograms for columns have skewed value .

FOR ALL INDEXES COLUMNS => collect histograms for columns have indexes.

Note: AUTO & SKEWONLY will let Oracle decide to create the Histograms or not.

Check the existence of Histograms:

SQL> select column_name, count(*) from dba_tab_histograms

where OWNER='SCOTT' table_name='EMP' group by column_name;

Drop Histograms: 11g

------------------

e.g.

SQL> Exec dbms_stats.delete_column_stats

(ownname=>'SH', tabname=>'SALES',

colname=>'PROD_ID', col_stat_type=> HISTOGRAM);

Stop gather Histograms: 11g

----------------------

[This will change the default table options]

e.g.

SQL> Exec dbms_stats.set_table_prefs

('SH', 'SALES','METHOD_OPT', 'FOR ALL COLUMNS SIZE AUTO,FOR COLUMNS SIZE 1 PROD_ID');

>Will continue to collect histograms as usual on all columns in the SALES table except for PROD_ID column.

Drop Histograms: 10g

------------------

e.g.

SQL> exec dbms_stats.delete_column_stats(user,'T','USERNAME');

##################################

Save/IMPORT & RESTORE STATISTICS:

##################################

===================

Export /Import Statistics:

===================

In this way statistics will be exported into table then imported later from that table.

1-Create STATS TABLE:

- -------------------------

SQL> Exec dbms_stats.create_stat_table(ownname => 'SYSTEM', stattab => 'prod_stats',tblspace => 'USERS');

2-Export the statistics to the STATS table:

---------------------------------------------

For Database stats:

SQL> Exec dbms_stats.export_database_stats(statown => 'SYSTEM', stattab => 'prod_stats');

For System stats:

SQL> Exec dbms_stats.export_SYSTEM_stats(statown => 'SYSTEM', stattab => 'prod_stats');

For Dictionary stats:

SQL> Exec dbms_stats.export_Dictionary_stats(statown => 'SYSTEM', stattab => 'prod_stats');

For Fixed Tables stats:

SQL> Exec dbms_stats.export_FIXED_OBJECTS_stats(statown => 'SYSTEM', stattab => 'prod_stats');

For Schema stas:

SQL> EXEC DBMS_STATS.EXPORT_SCHEMA_STATS('ORIGINAL_SCHEMA','STATS_TABLE',NULL,'STATS_TABLE_OWNER');

For Table:

SQL> Conn scott/tiger

SQL> Exec dbms_stats.export_TABLE_stats(ownname => 'SCOTT',tabname => 'EMP',stattab => 'prod_stats');

For Index:

SQL> Exec dbms_stats.export_INDEX_stats(ownname => 'SCOTT',indname => 'PK_EMP',stattab => 'prod_stats');

For Column:

SQL> Exec dbms_stats.export_COLUMN_stats (ownname=>'SCOTT',tabname=>'EMP',colname=>'EMPNO',stattab=>'prod_stats');

3-Import the statistics from PROD_STATS table to the dictionary:

--------------------------------------------------------------------

For Database stats:

SQL> Exec DBMS_STATS.IMPORT_DATABASE_STATS

(stattab => 'prod_stats',statown => 'SYSTEM');

For System stats:

SQL> Exec DBMS_STATS.IMPORT_SYSTEM_STATS

(stattab => 'prod_stats',statown => 'SYSTEM');

For Dictionary stats:

SQL> Exec DBMS_STATS.IMPORT_Dictionary_STATS

(stattab => 'prod_stats',statown => 'SYSTEM');

For Fixed Tables stats:

SQL> Exec DBMS_STATS.IMPORT_FIXED_OBJECTS_STATS

(stattab => 'prod_stats',statown => 'SYSTEM');

For Schema stats:

SQL> Exec DBMS_STATS.IMPORT_SCHEMA_STATS

(ownname => 'SCOTT',stattab => 'prod_stats', statown => 'SYSTEM');

For Table stats and it's indexes:

SQL> Exec dbms_stats.import_TABLE_stats

( ownname => 'SCOTT', stattab => 'prod_stats',tabname => 'EMP');

For Index:

SQL> Exec dbms_stats.import_INDEX_stats

( ownname => 'SCOTT', stattab => 'prod_stats', indname => 'PK_EMP');

For COLUMN:

SQL> Exec dbms_stats.import_COLUMN_stats

(ownname=>'SCOTT',tabname=>'EMP',colname=>'EMPNO',stattab=>'prod_stats');

4-Drop Stat Table:

-------------------

SQL> Exec dbms_stats.DROP_STAT_TABLE (stattab => 'prod_stats',ownname => 'SYSTEM');

===============

Restore statistics: -From Dictionary-

===============

Old statistics are saved automatically in SYSAUX for 31 day.

Restore Dictionary stats as of timestamp:

-----------------------------------------

SQL> Exec DBMS_STATS.RESTORE_DICTIONARY_STATS(sysdate-1);

Restore Database stats as of timestamp:

--------------------------------------

SQL> Exec DBMS_STATS.RESTORE_DATABASE_STATS(sysdate-1);

Restore SYSTEM stats as of timestamp:

--------------------------------------

SQL> Exec DBMS_STATS.RESTORE_SYSTEM_STATS(sysdate-1);

Restore FIXED OBJECTS stats as of timestamp:

-----------------------------------------------

SQL> Exec DBMS_STATS.RESTORE_FIXED_OBJECTS_STATS(sysdate-1);

Restore SCHEMA stats as of timestamp:

---------------------------------------

SQL> Exec dbms_stats.restore_SCHEMA_stats

(ownname=>'SYSADM',AS_OF_TIMESTAMP=>sysdate-1);

OR:

SQL> Exec dbms_stats.restore_schema_stats

(ownname=>'SYSADM',AS_OF_TIMESTAMP=>'20-JUL-2008 11:15:00AM');

Restore Table stats as of timestamp:

-----------------------------------

SQL> Exec DBMS_STATS.RESTORE_TABLE_STATS

(ownname=>'SYSADM', tabname=>'T01POHEAD',AS_OF_TIMESTAMP=>sysdate-1);

=========

Advanced:

=========

To Check current Stats history retention period (days):

-------------------------------------------------

SQL> select dbms_stats.get_stats_history_retention from dual;

SQL> select dbms_stats.get_stats_history_availability from dual;

To modify current Stats history retention period (days):

-------------------------------------------------

SQL> Exec dbms_stats.alter_stats_history_retention(60);

Purge statistics older than 10 days:

------------------------------

SQL> Exec DBMS_STATS.PURGE_STATS(SYSDATE-10);

Procedure To claim space after purging statstics:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Space will not be claimed automatically when you purge stats, you must claim it manually using this procedure:

Check Stats tables size:

>>>>>>

col Mb form 9,999,999

col SEGMENT_NAME form a40

col SEGMENT_TYPE form a6

set lines 120

select sum(bytes/1024/1024) Mb,

segment_name,segment_type from dba_segments

where tablespace_name = 'SYSAUX'

and segment_name like 'WRI$_OPTSTAT%'

and segment_type='TABLE'

group by segment_name,segment_type order by 1 asc

Check Stats indexes size:

>>>>>

col Mb form 9,999,999

col SEGMENT_NAME form a40

col SEGMENT_TYPE form a6

set lines 120

select sum(bytes/1024/1024) Mb, segment_name,segment_type

from dba_segments

where tablespace_name = 'SYSAUX'

and segment_name like '%OPT%'

and segment_type='INDEX'

group by segment_name,segment_type order by 1 asc

Move Stats tables in same tablespace:

>>>>>

select 'alter table '||segment_name||' move tablespace

SYSAUX;' from dba_segments

where tablespace_name = 'SYSAUX'

and segment_name like '%OPT%' and segment_type='TABLE'

Rebuild stats indexes:

>>>>>>

select 'alter index '||segment_name||' rebuild online;'

from dba_segments where tablespace_name = 'SYSAUX'

and segment_name like '%OPT%' and segment_type='INDEX'

Check for un-usable indexes:

>>>>>

select di.index_name,di.index_type,di.status from

dba_indexes di , dba_tables dt

where di.tablespace_name = 'SYSAUX'

and dt.table_name = di.table_name

and di.table_name like '%OPT%'

order by 1 asc

Delete Statistics:

===============

For Database stats:

SQL> Exec DBMS_STATS.DELETE_DATABASE_STATS ();

For System stats:

SQL> Exec DBMS_STATS.DELETE_SYSTEM_STATS ();

For Dictionary stats:

SQL> Exec DBMS_STATS.DELETE_DICTIONARY_STATS ();

For Fixed Tables stats:

SQL> Exec DBMS_STATS.DELETE_FIXED_OBJECTS_STATS ();

For Schema stats:

SQL> Exec DBMS_STATS.DELETE_SCHEMA_STATS ('SCOTT');

For Table stats and it's indexes:

SQL> Exec dbms_stats.DELETE_TABLE_stats(ownname=>'SCOTT',tabname=>'EMP');

For Index:

SQL> Exec dbms_stats.DELETE_INDEX_stats(ownname => 'SCOTT',indname => 'PK_EMP');

For Column:

SQL> Exec dbms_stats.DELETE_COLUMN_stats(ownname =>'SCOTT',tabname=>'EMP',colname=>'EMPNO');

Note: This procedure can be rollback by restoring STATS using DBMS_STATS.RESTORE_ procedure.

Pending Statistics: "11g onwards"

===============

What is Pending Statistics:

Pending statistics is a feature let you test the new gathered statistics without letting the CBO (Cost Based Optimizer) use them "system wide" unless you publish them.

How to use Pending Statistics:

Switch on pending statistics mode:

SQL> Exec DBMS_STATS.SET_GLOBAL_PREFS('PUBLISH','FALSE');

Note: Any new statistics will be gathered on the database will be marked PENDING unless you change back the previous parameter to true:

SQL> Exec DBMS_STATS.SET_GLOBAL_PREFS('PUBLISH','TRUE');

Gather statistics: "as you used to do"

SQL> Exec DBMS_STATS.GATHER_TABLE_STATS('sh','SALES');

Enable using pending statistics on your session only:

SQL> Alter session set optimizer_use_pending_statistics=TRUE;

Then any SQL statement you will run will use the new pending statistics...

When proven OK, publish the pending statistics:

SQL> Exec DBMS_STATS.PUBLISH_PENDING_STATS();

Once you finish don't forget to return the Global PUBLISH parameter to TRUE:

SQL> Exec DBMS_STATS.SET_GLOBAL_PREFS('PUBLISH','TRUE');

>If you didn't do so, all new gathered statistics on the database will be marked as PENDING, the thing may confuse you or any DBA working on this DB in case he is not aware of that parameter change.

Reference:

http://docs.oracle.com/cd/E18283_01/appdev.112/e16760/d_stats.htm

This task became an automated task starting from 10g, To check the status of that task:

SQL> select * from dba_autotask_client where client_name = "auto optimizer stats collection" ;

As per Oracle documentation, this task gathers statistics on all objects in the database which have stale or missing statistics.

Also you can:

Enable automatic optimizer statistics:

SQL> BEGIN

DBMS_AUTO_TASK_ADMIN.ENABLE(

client_name => 'auto optimizer stats collection',

operation => NULL,

window_name => NULL);

END;

Disable automatic optimizer statistics:

SQL> BEGIN

DBMS_AUTO_TASK_ADMIN.DISABLE(

client_name => 'auto optimizer stats collection',

operation => NULL,

window_name => NULL);

END;

To check the tables that have stale statistics:

SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES';

I've updated the post with these information, I recommend you to check this reference:

http://docs.oracle.com/cd/B28359_01/server.111/b28274/stats.htm#i41282

Wednesday, April 24, 2013

Handling Block Corruptions

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.

{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.
See note 144911.1 for an example.

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.

Script To Run DBV On All Datafiles Of the Database

This script will simplify the task of running DBV on the all datafiles of a database.

When user experiences ORA-01578 / ORA-08103 or any other kind of corrupt messages this utility can be used to scan the datafiles at OS level.

We need to have the database atleast in MOUNT stage to perform this operation.

Configuring the Script

mkdir /tmp/dbvlogs
cd /tmp/dbvlogs

Running the Script

As a first step run the following script from sqlplus which will generate the script for DBV

sqlplus /nolog
connect / as sysdba
set feedback off
set head off
set echo off
set linesize 200
set pagesize 2500
spool /tmp/dbvlogs/dbvchk.sh
select 'dbv file=' || name || ' blocksize='|| block_size || ' logfile=' ||
substr(name, instr(name, '/', -1, 1) +1) ||
'.' || file# ||  '.log'  from v$datafile
/
spool off

Incase if datafiles are in RAW devices, then we need to mention the END parameter in DBV.
You can use the following query incase if you are using RAW devices.

select 'dbv file=' || name || ' blocksize='|| block_size || ' end=' ||(bytes/block_size) ||' logfile=' ||
substr(name, instr(name, '/', -1, 1) +1) ||
'.' || file# ||  '.log'  from v$datafile
/

-- For Windows the following modification is required

select 'dbv file=' || name || ' blocksize='|| block_size ||
' logfile=' || substr(name, instr(name, '\', -1, 1) +1) ||
'.' || file# || '.log' from v$datafile
/

If ASM storage being used, we need to specify USERID to get authenticated on ASM Instance.
You can use following query if you are running in ASM storage.

select 'dbv file=' || name || ' blocksize='|| block_size || ' USERID=sys/&SYS_PASSWORD logfile=' ||
substr(name, instr(name, '/', -1, 1) +1) ||
'.' || file# || '.log' from v$datafile
/

Script

Now you need to run the dbv commands for all the datafiles, which is spooled to dbvchk.sh.

Please proof read this script before executing the same.

$ cd /tmp/dbvlogs
$ chmod 755 dbvchk.sh
$ ./dbvchk.sh

In case of Windows, just run the above file. Its more appropriate to have a .bat extention for windows.

If you have a tar logged then, compress the log files, upload the above compressed file to metalink.

$ tar cvf dbvlogs.tar *.log
$ compress dbvlogs.tar.Z

In case of Windows operating system, simply use the winzip utility to compress the files.

Script Output

As per the above script the dbv logs will be generated under /tmp/dbvlogs directory.
The files will have the name as follows.

For system datafile with the name /tmp/system.dbf and file# 1 the logfile will have the name like.

/tmp/dbvlogs/system.dbf.1.log

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