Working with Redo Logs

Script to View Online RedoLog Information :

SQL> SELECT * FROM V$LOGFILE;

OR

SQL > SELECT a.group#

,a.thread# ,a.status grp_status

,b.member member ,b.status mem_status

,a.bytes/1024/1024 mbytes FROM v$log a, v$logfile b

WHERE a.group# = b.group#

ORDER BY a.group#, b.member;

Status for Online Redo Log of V$LOG View  :

CURRENT The log group is currently being written to by the log writer.

ACTIVE The log group is required for crash recovery and may or may not have been archived.

CLEARING The log group is being cleared out by an ALTER DATABASE CLEAR LOGFILE command.

CLEARING_CURRENT The current log group is being cleared of a closed thread.

INACTIVE The log group isn’t required for crash recovery and may or may not have been archived.

UNUSED The log group has never been written to; it was recently created.

Status of Online Redo Log File Members in V$LOGFILE View

INVALID The log file member is inaccessible or has been recently created.

DELETED The log file member is no longer in use.

STALE The log file member’s contents aren’t complete.

NULL The log file member is being used by the database.

How to Rename the Redolog files:

1 . Shut down the DB

2. Rename the redolog files on OS level (using ‘mv’ command in UNIX)

3. Startup mount

SQL> alter database rename file ‘<loc with prev file name> to <loc with current file name>;

Do the same for all renamed redolog files

SQL> alter database open;

How to Multiplex the redolog files:

To protect against a failure involving the redo log itself, Oracle Database allows a multiplexed redo log, meaning that two or more identical copies of the redo log can be automatically maintained in separate locations. For the most benefit, these locations should be on separate disks. Even if all copies of the redo log are on the same disk, however, the redundancy can help protect against I/O errors, file corruption, and so on. When redo log files are multiplexed, LGWR concurrently writes the same redo log information to multiple identical redo log files, thereby eliminating a single point of redo log failure.

Multiplexing is implemented by creating groups of redo log files. A group consists of a redo log file and its multiplexed copies. Each identical copy is said to be a member of the group. Each redo log group is defined by a number, such as group 1, group 2, and so on.

FOR EXAMPLE:

In group 1 all memebers will have same type of data, if one member is corrupted then another member is user for recovery

SQL> SELECT MEMBER FROM V$LOGFILE WHERE GROUP# = ‘1’;

SQL>ALTER DATABASE ADD LOGFILE MEMBER ‘<>loc with redolog file name> TO GROUP <group_num>;

Decommission of Oracle Database

Decommission : A process to remove, Retire or making it inactive

Every organization has their own documents (SOP – Standard Operation Procedure) maintain for  removing or decommissioning the active  databases

I am presenting some general steps below.

1.      Requirement : Business/Customer to proceed for database decommissioning.

2.    Notifying Business/Customer / Application team that  “we are going to decommission the database at _ _ specific time” .

3.      Making the fresh backup :  Raise a ticket and assign it to Storage / Backup team and Co-ordinate with storage / backup team to take required backup. And to keep the backup for specified time(retention period).

4.      Make a list of parameter file, datafiles, controlfiles, redolog files.

-          Details of DB links using query: select * from dba_db_links;

-          List of all the data files using query: select * from dba_data_files;

-          List of log files using query: select * from v$logfile;

-          List of control files using query: select * from v$controlfile;

5.      Bring down the database and stop the listener.

6.      Take whole database backup and make sure backup is completed without any errors/warnings.

7.    Make sure Storage team has taken the backup as specified in the raised ticket against them and has set the retention period correctly. You can take a Signoff mail from Storage/Backup team in case it is required.

8.   Remove the monitoring jobs entry from crontab and also remove the monitoring jobs (if any) running from third party tool(s) in the database and comment out the entry from oratab file located in /etc directory.

9.   Mark in your database repository/inventory or your DB records , that this specific Database is going to Decom under this specific request at this specific time. (This will help to notify other DBA in your team).

10.   Startup the database in restrict mode and give drop database command.

                        SQL> startup restrict mount ;

                        SQL> drop database;

11.  Check if the instance is still running or not. Shutdown the instance if it is still running. Check and verify Alertlog for the list of files deleted.

12. Now remove the tracefiles, archive log files, dump files, old backup files and respective Database directories.

13.  Be careful before deleting the physical files. Crosscheck and verify before deleting these file.

14.  Now remove the backup “entry” through which backup was getting triggered.

15.  Notify the customer/Application team about the backup ticket , backup information such as retention period and location of backup.

Note : Retention Period may be varied based on your business needs and SLA

See Also :

- Dataguard Creation

- Pre-Check for Dataguard SwitchOver  

- Common Wait events in AWR and Solutions 

- Most Common Daily Datapump Scenarios

Health check for DB

This Script is obviously NOT written by me. One of my best buddy shared this with me.

So im sharing this with you.

                                                                                                    

Step 1. Make a sql script-file using VI editor.

SQL> exit

 [oracle@oracleasm1 u01]$

 [oracle@oracleasm1 u01]$ vi hc_script.sql

 

Step 2. Paste the below Content.

title 'SYSTEM STATISTICS' 

select 'LIBRARY CACHE STATISTICS:' from dual; 

ttitle off 

select 'PINS - # of times an item in the library cache was executed - '|| 
        sum(pins), 
       'RELOADS - # of library cache misses on execution steps - '||
        sum (reloads), 
       'RELOADS / PINS * 100 = '||round((sum(reloads) / sum(pins) * 
100),2)||'%'
from    v$librarycache 
/ 

prompt Increase memory until RELOADS is near 0 but watch out for 
prompt Paging/swapping
prompt To increase library cache, increase SHARED_POOL_SIZE 
prompt 
prompt ** NOTE: Increasing SHARED_POOL_SIZE will increase the SGA size. 
prompt 
prompt Library Cache Misses indicate that the Shared Pool is not big 
prompt enough to hold the shared SQL area for all concurrently open cursors. 
prompt If you have no Library Cache misses (PINS = 0), you may get a small 
prompt increase in performance by setting CURSOR_SPACE_FOR_TIME = TRUE which 
prompt prevents ORACLE from deallocating a shared SQL area while an 
prompt application 
prompt cursor associated with it is open. 
prompt 
prompt For Multi-threaded server, add 1K to SHARED_POOL_SIZE per user. 
prompt 
prompt------------------------------------------------------------------------ 

column xn1 format a50 
column xn2 format a50 
column xn3 format a50 
column xv1 new_value xxv1 noprint 
column xv2 new_value xxv2 noprint 
column xv3 new_value xxv3 noprint 
column d1  format a50 
column d2  format a50 

prompt HIT RATIO: 
prompt 
prompt Values Hit Ratio is calculated against: 
prompt 

select lpad(name,20,' ')||'  =  '||value xn1, value xv1 
from   v$sysstat 
where  name = 'db block gets' 
/ 

select lpad(name,20,' ')||'  =  '||value xn2, value xv2 
from   v$sysstat 
where  name = 'consistent gets' 
/ 

select lpad(name,20,' ')||'  =  '||value xn3, value xv3 
from   v$sysstat b 
where  name = 'physical reads' 
/ 

set pages 60 

select 'Logical reads = db block gets + consistent gets ', 
        lpad ('Logical Reads = ',24,' ')||to_char(&xxv1+&xxv2) d1 
from    dual 
/ 

select 'Hit Ratio = (logical reads - physical reads) / logical reads', 
        lpad('Hit Ratio = ',24,' ')|| 
        round( (((&xxv2+&xxv1) - &xxv3) / (&xxv2+&xxv1))*100,2 )||'%' d2 
from    dual 
/ 

prompt If the hit ratio is less than 60%-70%, increase the initialization 
prompt parameter DB_BLOCK_BUFFERS.  ** NOTE:  Increasing this parameter will 
prompt increase the SGA size. 
prompt 
prompt------------------------------------------------------------------------ 

col name format a30 
col gets format 9,999,999,999,999 
col waits format 9,999,999,999,999 

prompt ROLLBACK CONTENTION STATISTICS: 
prompt 

prompt GETS - # of gets on the rollback segment header
prompt WAITS - # of waits for the rollback segment header 

set head on; 

select name, waits, gets 
from   v$rollstat, v$rollname 
where  v$rollstat.usn = v$rollname.usn 
/ 

set head off 

select 'The average of waits/gets is '|| 
   round((sum(waits) / sum(gets)) * 100,2)||'%' 
From    v$rollstat 
/ 

prompt 
prompt If the ratio of waits to gets is more than 1% or 2%, consider 
prompt creating more rollback segments 
prompt 
prompt Another way to gauge rollback contention is: 
prompt 

column xn1 format 9999999999 
column xv1 new_value xxv1 noprint 

set head on 

select class, count 
from   v$waitstat 
where  class in ('system undo header', 'system undo block',
                 'undo header',        'undo block'          ) 
/ 

set head off 

select 'Total requests = '||sum(count) xn1, sum(count) xv1 
from    v$waitstat 
/ 

select 'Contention for system undo header = '|| 
       (round(count/(&xxv1+0.00000000001),4)) * 100||'%' 
from  v$waitstat 
where   class = 'system undo header' 
/ 

select 'Contention for system undo block = '|| 
       (round(count/(&xxv1+0.00000000001),4)) * 100||'%' 
from    v$waitstat 
where   class = 'system undo block' 
/ 

select 'Contention for undo header = '|| 
       (round(count/(&xxv1+0.00000000001),4)) * 100||'%' 
from    v$waitstat 
where   class = 'undo header' 
/ 

select 'Contention for undo block = '|| 
       (round(count/(&xxv1+0.00000000001),4)) * 100||'%' 
from    v$waitstat 
where   class = 'undo block' 
/ 

prompt 
prompt If the percentage for an area is more than 1% or 2%, consider 
prompt creating more rollback segments.  Note:  This value is usually very 
prompt small
prompt and has been rounded to 4 places. 
prompt 
prompt------------------------------------------------------------------------ 

prompt REDO CONTENTION STATISTICS: 
prompt 
prompt The following shows how often user processes had to wait for space in 
prompt the redo log buffer: 

select name||' = '||value 
from   v$sysstat 
where  name = 'redo log space requests' 
/ 

prompt 
prompt This value should be near 0.  If this value increments consistently, 
prompt processes have had to wait for space in the redo buffer.  If this 
prompt condition exists over time, increase the size of LOG_BUFFER in the 
prompt init.ora file in increments of 5% until the value nears 0. 
prompt ** NOTE: increasing the LOG_BUFFER value will increase total SGA size. 
prompt 
prompt ----------------------------------------------------------------------- 


col name format a15 
col gets format 99999999999 
col misses format 999999999999 
col immediate_gets heading 'IMMED GETS' format 999999999999 
col immediate_misses heading 'IMMED MISS' format 999999999999 
col sleeps format 999999 

prompt LATCH CONTENTION: 
prompt 
prompt GETS - # of successful willing-to-wait requests for a latch 
prompt MISSES - # of times an initial willing-to-wait request was unsuccessful 
prompt IMMEDIATE_GETS - # of successful immediate requests for each latch 
prompt IMMEDIATE_MISSES = # of unsuccessful immediate requests for each latch 
prompt SLEEPS - # of times a process waited and requests a latch after an 
prompt          initial willing-to-wait request 
prompt 
prompt If the latch requested with a willing-to-wait request is not 
prompt available, the requesting process waits a short time and requests 
prompt again. 
prompt If the latch requested with an immediate request is not available, 
prompt the requesting process does not wait, but continues processing 
prompt 

set head on 

select name,          gets,              misses, 
       immediate_gets,  immediate_misses,  sleeps 
from   v$latch 
where  name in ('redo allocation',  'redo copy') 
/ 

set head off 

select 'Ratio of MISSES to GETS: '|| 
        round((sum(misses)/(sum(gets)+0.00000000001) * 100),2)||'%' 
from    v$latch 
where   name in ('redo allocation',  'redo copy') 
/ 

select 'Ratio of IMMEDIATE_MISSES to IMMEDIATE_GETS: '|| 
        round((sum(immediate_misses)/ 
       (sum(immediate_misses+immediate_gets)+0.00000000001) * 100),2)||'%' 
from    v$latch 
where   name in ('redo allocation',  'redo copy') 
/ 

prompt 
prompt If either ratio exceeds 1%, performance will be affected. 
prompt 
prompt Decreasing the size of LOG_SMALL_ENTRY_MAX_SIZE reduces the number of 
prompt processes copying information on the redo allocation latch. 
prompt 
prompt Increasing the size of LOG_SIMULTANEOUS_COPIES will reduce contention 
prompt for redo copy latches. 

rem 
rem This shows the library cache reloads 
rem 

set head on 

prompt 
prompt------------------------------------------------------------------------ 

prompt 
prompt Look at gethitratio and pinhit ratio 
prompt 
prompt GETHITRATIO is number of GETHTS/GETS 
prompt PINHIT RATIO is number of PINHITS/PINS - number close to 1 indicates 
prompt that most objects requested for pinning have been cached.  Pay close 
prompt attention to PINHIT RATIO. 
prompt 

column namespace    format a20   heading 'NAME' 
column gets         format 99999999999 heading 'GETS' 
column gethits      format 99999999999 heading 'GETHITS' 
column gethitratio  format 999.99   heading 'GET HIT|RATIO' 
column pins         format 99999999999  heading 'PINHITS' 
column pinhitratio  format 999.99   heading 'PIN HIT|RATIO' 

select namespace,    gets,  gethits, 
       gethitratio,  pins,  pinhitratio 
from   v$librarycache 
/ 

rem 
rem 
rem This looks at the dictionary cache miss rate 
rem 

prompt 
prompt------------------------------------------------------------------------ 

prompt THE DATA DICTIONARY CACHE: 
prompt 
prompt 
prompt Consider keeping this below 5% to keep the data dictionary cache in 
prompt the SGA.  Up the SHARED_POOL_SIZE to improve this statistic. **NOTE: 
prompt increasing the SHARED_POOL_SIZE will increase the SGA. 
prompt 

column dictcache format 999.99 heading 'Dictionary Cache | Ratio %' 

select sum(getmisses) / (sum(gets)+0.00000000001) * 100 dictcache 
from   v$rowcache 
/ 

prompt 
prompt------------------------------------------------------------------------ 

prompt 
prompt SYSTEM EVENTS: 
prompt 
prompt Not sure of the value of this section yet but it looks interesting. 
prompt 

col event format a37 heading 'Event' 
col total_waits format 999999999999 heading 'Total|Waits' 
col time_waited format 99999999999999 heading 'Time Wait|In Hndrds' 
col total_timeouts format 9999999999 heading 'Timeout' 
col average_wait heading 'Average|Time' format 999999999.999 

set pages 999 

select * 
from   v$system_event 
/ 

prompt 
prompt------------------------------------------------------------------------ 

rem 
rem 
rem This looks at the sga area breakdown 
rem 

prompt THE SGA AREA ALLOCATION: 
prompt 
prompt 
prompt This shows the allocation of SGA storage.  Examine this before and 
prompt after making changes in the INIT.ORA file which will impact the SGA. 
prompt 

col name format a40 

select name, bytes 
from   v$sgastat 
/ 

set head off 

select 'total of SGA                            '||sum(bytes) 
from    v$sgastat 
/

prompt 
prompt------------------------------------------------------------------------ 

rem 
rem Displays all the base session statistics 
rem 

set head on 
set pagesize 110 

column name        format a55            heading 'Statistic Name' 
column value       format 9,999,999,999,999,999  heading 'Result' 
column statistic#  format 999999999           heading 'Stat#'

ttitle center 'Instance Statistics' skip 2 

prompt 
prompt Below is a dump of the core Instance Statistics that are greater than0. 
prompt Although there are a great many statistics listed, the ones of greatest 
prompt value are displayed in other formats throughout this report.  Of 
prompt interest here are the values for: 
prompt 
prompt  cumulative logons 
prompt(# of actual connections to the DB since last startup - good 
prompt  volume-of-use statistic) 
prompt 
prompt  #93  table fetch continued row 
prompt  (# of chained rows - will be higher if there are a lot of long fields 
prompt  if the value goes up over time, it is a good signaller of general 
prompt  database fragmentation) 
prompt 

select statistic#,  name,  value 
from   v$sysstat 
where  value > 0 
/ 

prompt 
prompt ----------------------------------------------------------------------- 

set pages 66; 
set space 3; 
set heading on; 

prompt 
prompt Parse Ratio usually falls between 1.15 and 1.45.  If it is higher, then 
prompt it is usually a sign of poorly written Pro* programs or unoptimized 
prompt SQL*Forms applications. 
prompt 
prompt Recursive Call Ratio will usually be between 
prompt 
prompt   7.0 - 10.0 for tuned production systems 
prompt  10.0 - 14.5 for tuned development systems 
prompt 
prompt Buffer Hit Ratio is dependent upon RDBMS size, SGA size and 
prompt the types of applications being processed.  This shows the %-age 
prompt of logical reads from the SGA as opposed to total reads - the 
prompt figure should be as high as possible.  The hit ratio can be raised 
prompt by increasing DB_BUFFERS, which increases SGA size.  By turning on 
prompt the "Virtual Buffer Manager" (db_block_lru_statistics = TRUE and 
prompt db_block_lru_extended_statistics = TRUE in the init.ora parameters), 
prompt you can determine how many extra hits you would get from memory as 
prompt opposed to physical I/O from disk.  **NOTE:  Turning these on will 
prompt impact performance.  One shift of statistics gathering should be enough 
prompt to get the required information. 
prompt 

ttitle left 'Ratios for this Instance' skip 2 

column pcc   heading 'Parse|Ratio'       format 99.99 
column rcc   heading 'Recsv|Cursr'       format 99.99 
column hr    heading 'Buffer|Ratio'      format 999,999,999,999,999.999 
column rwr   heading 'Rd/Wr|Ratio'       format 999,999,999.9 
column bpfts heading 'Blks per|Full TS'  format 999,999,999

REM Modified for O7.1 to reverse 'cumulative opened cursors' to 
REM 'opened cursors cumulative' 
REM was:sum(decode(a.name,'cumulative opened cursors',value, .00000000001)) 
REM pcc, 
REM and:sum(decode(a.name,'cumulative opened cursors',value,.00000000001)) 
REM rcc, 

select sum(decode(a.name,'parse count',value,0)) / 
       sum(decode(a.name,'opened cursors cumulative',value,.00000000001)) pcc, 
       sum(decode(a.name,'recursive calls',value,0)) / 
       sum(decode(a.name,'opened cursors cumulative',value,.00000000001)) rcc, 
       (1-(sum(decode(a.name,'physical reads',value,0)) / 
       sum(decode(a.name,'db block gets',value,.00000000001)) + 
  sum(decode(a.name,'consistent gets',value,0))) * (-1)) hr, 
       sum(decode(a.name,'physical reads',value,0)) / 
       sum(decode(a.name,'physical writes',value,.00000000001)) rwr, 
       (sum(decode(a.name,'table scan blocks gotten',value,0)) - 
       sum(decode(a.name,'table scans (short tables)',value,0)) * 4) / 
       sum(decode(a.name,'table scans (long tables)',value,.00000000001)) 
bpfts 
from   v$sysstat a 
/ 

prompt 
prompt ----------------------------------------------------------------- 
prompt This looks at overall i/o activity against individual 
prompt files within a tablespace 
prompt 
prompt Look for a mismatch across disk drives in terms of I/O 
prompt 
prompt Also, examine the Blocks per Read Ratio for heavily accessed 
prompt TSs - if this value is significantly above 1 then you may have 
prompt full tablescans occurring (with multi-block I/O) 
prompt 
prompt If activity on the files is unbalanced, move files around to balance 
prompt the load.  Should see an approximately even set of numbers across files 
prompt 

set pagesize 100; 
set space 1 

column pbr       format 999999999999  heading 'Physical|Blk Read' 
column pbw       format 9999999999    heading 'Physical|Blks Wrtn' 
column pyr       format 9999999999    heading 'Physical|Reads' 
column readtim   format 999999999999  heading 'Read|Time' 
column name      format a40       heading 'DataFile Name' 
column writetim  format 999999999999  heading 'Write|Time' 

ttitle center 'Tablespace Report' skip 2 

compute sum of f.phyblkrd, f.phyblkwrt on report 

select fs.name name,  f.phyblkrd pbr,  f.phyblkwrt pbw,
       f.readtim,     f.writetim 
from   v$filestat f, v$datafile fs 
where  f.file#  =  fs.file# 
order  by fs.name 
/ 

prompt 
prompt ----------------------------------------------------------------- 

prompt GENERATING WAIT STATISTICS: 
prompt 
prompt This will show wait stats for certain kernel instances.  This 
prompt may show the need for additional rbs, wait lists, db_buffers 
prompt 
 ttitle center 'Wait Statistics for the Instance' skip 2 

column class  heading 'Class Type' 
column count  heading 'Times Waited'  format 99,999,999,999,999
column time   heading 'Total Times'   format 99,999,999,999,999 

select class,  count,  time 
from   v$waitstat 
where  count > 0 
order  by class 
/ 

prompt 
prompt Look at the wait statistics generated above (if any). They will 
prompt tell you where there is contention in the system.  There will 
prompt usually be some contention in any system - but if the ratio of 
prompt waits for a particular operation starts to rise, you may need to 
prompt add additional resource, such as more database buffers, log buffers, 
prompt or rollback segments 
prompt 
prompt ----------------------------------------------------------------- 

prompt ROLLBACK STATISTICS: 
prompt 

ttitle off; 

set linesize 80 

column extents    format 999,999        heading 'Extents' 
column rssize     format 999,999,999,999  heading 'Size in|Bytes' 
column optsize    format 999,999,999,999  heading 'Optimal|Size' 
column hwmsize    format 99,999,999,999   heading 'High Water|Mark' 
column shrinks    format 999,999        heading 'Num of|Shrinks' 
column wraps      format 999,999        heading 'Num of|Wraps' 
column extends    format 999,999,999      heading 'Num of|Extends' 
column aveactive  format 999,999,999,999  heading 'Average size|Active Extents' 
column rownum noprint 

select rssize,    optsize,  hwmsize, 
       shrinks,   wraps,    extends,  aveactive 
from   v$rollstat 
order  by rownum 
/ 

prompt 
prompt ----------------------------------------------------------------- 

set linesize 80 

break on report 

compute sum of gets waits writes on report 

ttitle center 'Rollback Statistics' skip 2 

select rownum,  extents,  rssize, 
       xacts,   gets,     waits,   writes 
from   v$rollstat 
order  by rownum 
/ 

ttitle off 

set heading off 

prompt 
prompt ----------------------------------------------------------------- 

prompt 
prompt SORT AREA SIZE VALUES: 
prompt 
prompt To make best use of sort memory, the initial extent of your Users 
prompt sort-work Tablespace should be sufficient to hold at least one sort 
prompt run from memory to reduce dynamic space allocation.  If you are getting 
prompt a high ratio of disk sorts as opposed to memory sorts, setting 
prompt sort_area_retained_size = 0 in init.ora will force the sort area to be 
prompt released immediately after a sort finishes. 
prompt 

column value format 999,999,999,999 

select 'INIT.ORA sort_area_size: '||value 
from    v$parameter 
where   name like 'sort_area_size'
/

select a.name,  value 
from   v$statname a,  v$sysstat 
where  a.statistic#  =   v$sysstat.statistic# 
and    a.name        in ('sorts (disk)', 'sorts (memory)', 'sorts (rows)') 
/ 

prompt 
prompt ----------------------------------------------------------------- 

set heading on 
set space 2 

prompt 
prompt This looks at Tablespace Sizing - Total bytes and free bytes 
prompt 

ttitle center 'Tablespace Sizing Information' Skip 2 

column tablespace_name  format a30            heading 'TS Name' 
column sbytes           format 9,999,999,999,999  heading 'Total Bytes' 
column fbytes           format 9,999,999,999,9999  heading 'Free Bytes' 
column kount            format 999,999            heading 'Ext' 

compute sum of fbytes on tablespace_name 
compute sum of sbytes on tablespace_name 
compute sum of sbytes on report 
compute sum of fbytes on report 

break on report 

select a.tablespace_name,    a.bytes sbytes, 
       sum(b.bytes) fbytes,  count(*) kount 
from   dba_data_files a,  dba_free_space b 
where  a.file_id  =  b.file_id 
group  by a.tablespace_name, a.bytes 
order  by a.tablespace_name 
/ 

set linesize 80 

prompt 
prompt A large number of Free Chunks indicates that the tablespace may need 
prompt to be defragmented and compressed. 
prompt 
prompt ----------------------------------------------------------------- 

set heading off 

ttitle off 

column value format 99,999,999,999,999 

select 'Total Physical Reads', value 
from    v$sysstat 
where   statistic# = 39 
/ 

prompt 
prompt If you can significantly reduce physical reads by adding incremental 
prompt data buffers...do it.  To determine whether adding data buffers will 
prompt help, set db_block_lru_statistics = TRUE and 
prompt db_block_lru_extended_statistics = TRUE in the init.ora parameters. 
prompt You can determine how many extra hits you would get from memory as 
prompt opposed to physical I/O from disk.  **NOTE:  Turning these on will 
prompt impact performance.  One shift of statistics gathering should be enough 
prompt to get the required information. 
prompt 

set heading on 

clear computes 

ttitle off 

prompt 
prompt ----------------------------------------------------------------- 
prompt CHECKING FOR FRAGMENTED DATABASE OBJECTS: 
prompt 
prompt Fragmentation report - If number of extents is approaching Maxextents, 
prompt it is time to defragment the table. 
prompt 

column owner  noprint  new_value  owner_var 
column segment_name  format a30          heading 'Object Name' 
column segment_type  format a9           heading 'Table/Indx' 
column sum(bytes)    format 999,999,999,999  heading 'Bytes Used' 
column count(*)      format 999,999          heading 'No.' 

break on owner skip page 2 

ttitle center 'Table Fragmentation Report' skip 2 - 
       left 'creator: ' owner_var skip 2 

select a.owner,     segment_name,  segment_type, 
    sum(bytes),  max_extents,   count(*) 
from   dba_extents a,  dba_tables b 
where  segment_name  =  b.table_name 
having count(*) > 3 
group  by a.owner, segment_name, segment_type, max_extents 
order  by a.owner, segment_name, segment_type, max_extents 
/ 

ttitle center 'Index Fragmentation Report' skip 2 - 
  left 'creator: ' owner_var skip 2 

select a.owner,     segment_name,  segment_type,
       sum(bytes),  max_extents,   count(*) 
from   dba_extents a, dba_indexes b 
where  segment_name = index_name 
having count(*) > 3 
group  by a.owner, segment_name, segment_type, max_extents 
order  by a.owner, segment_name, segment_type, max_extents 
/ 

prompt 
prompt ----------------------------------------------------------------- 

spool off

Step 3. Execute the script.

SQL > @/u01/hc_script.sql  

See Also  :  Health Check – When the Application Users complaints for an issue