LOGGING or NOLOGGING, that is the question – Part VIII
By Francisco Munoz Alvarez 
How to find Sessions Generating Lots of Redo
To find sessions generating lots of redo, you can use either of the following methods. Both methods examine the amount of undo generated. When a transaction generates undo, it will automatically generate redo as well.
The methods are:
1) Query V$SESS_IO. This view contains the column BLOCK_CHANGES which indicates how much blocks have been changed by the session. High values indicate a session generating lots of redo.
The query you can use is:
SQL> SELECT s.sid, s.serial#, s.username, s.program,
2 i.block_changes
3 FROM v$session s, v$sess_io i
4 WHERE s.sid = i.sid
5 ORDER BY 5 desc, 1, 2, 3, 4;
Run the query multiple times and examine the delta between each occurrence of BLOCK_CHANGES. Large deltas indicate high redo generation by the session.
2) Query V$TRANSACTION. These view contains information about the amount of undo blocks and undo records accessed by the transaction (as found in the USED_UBLK and USED_UREC columns).
The query you can use is:
SQL> SELECT s.sid, s.serial#, s.username, s.program,
2 t.used_ublk, t.used_urec
3 FROM v$session s, v$transaction t
4 WHERE s.taddr = t.addr
5 ORDER BY 5 desc, 6 desc, 1, 2, 3, 4;
Run the query multiple times and examine the delta between each occurrence of USED_UBLK and USED_UREC. Large deltas indicate high redo generation by the session.
You use the first query when you need to check for programs generating lots of redo when these programs activate more than one transaction. The latter query can be used to find out which particular transactions are generating redo.
Useful Scripts
To see the redo generated since instance started:
col name format a30 heading ‘Statistic|Name’
col value heading ‘Statistic|Value’
start title80 “Redo Log Statistics”
spool rep_out\&db\red_stat
SELECT name, value
FROM v$sysstat
WHERE name like ‘%redo%’
order by name
/
spool off
pause Press enter to continue
ttitle off
The redo generated during my session since the session started:
select value redo_size
from v$mystat, v$statname
where v$mystat.STATISTIC# = v$statname.STATISTIC#
and name = ‘redo size’
/
The redo generated by current user sessions:
select v$session.sid, username, value redo_size
from v$sesstat, v$statname, v$session
where v$sesstat.STATISTIC# = v$statname.STATISTIC#
and v$session.sid = v$sesstat.sid
and name = ‘redo size’
and value > 0
and username is not null
order by value
/
Provide a current status for redo logs:
column first_change# format 999,999,999 heading Change#
column group# format 9,999 heading Grp#
column thread# format 999 heading Th#
column sequence# format 999,999 heading Seq#
column members format 999 heading Mem
column archived format a4 heading Arc?
column first_time format a25 heading First|Time
break on thread#
set pages 60 lines 132 feedback off
start title132 ‘Current Redo Log Status’
spool rep_out\&db\log_stat
select thread#, group#, sequence#,
bytes, members,archived,status,first_change#,
to_char(first_time,’dd-mon-yyyy hh24:mi’) first_time
from sys.v_$log
order by thread#, group#;
spool off
pause Press Enter to continue
set pages 22 lines 80 feedback on
clear breaks
clear columns
ttitle off
/
Provide redo log groups and log switch (archive generation) information:
set echo on
set linesize 150
set pagesize 500
column day format a16 heading ‘Dia’
column d_0 format a3 heading ‘00′
column d_1 format a3 heading ‘01′
column d_2 format a3 heading ‘02′
column d_3 format a3 heading ‘03′
column d_4 format a3 heading ‘04′
column d_5 format a3 heading ‘05′
column d_6 format a3 heading ‘06′
column d_7 format a3 heading ‘07′
column d_8 format a3 heading ‘08′
column d_9 format a3 heading ‘09′
column d_10 format a3 heading ‘10′
column d_11 format a3 heading ‘11′
column d_12 format a3 heading ‘12′
column d_13 format a3 heading ‘13′
column d_14 format a3 heading ‘14′
column d_15 format a3 heading ‘15′
column d_16 format a3 heading ‘16′
column d_17 format a3 heading ‘17′
column d_18 format a3 heading ‘18′
column d_19 format a3 heading ‘19′
column d_20 format a3 heading ‘20′
column d_21 format a3 heading ‘21′
column d_22 format a3 heading ‘22′
column d_23 format a3 heading ‘23′
column Total format 9999
column status format a8
column member format a40
column archived heading ‘Archived’ format a8
column bytes heading ‘Bytes|(MB)’ format 9999
Ttitle ‘Log Info’ skip 2
select l.group#,f.member,l.archived,l.bytes/1078576 bytes,l.status,f.type
from v$log l, v$logfile f
where l.group# = f.group#
/
Ttitle off
prompt =========================================================================================================================
Ttitle ‘Log Switch on hour basis’ skip 2
select to_char(FIRST_TIME,’DY, DD-MON-YYYY’) dia,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’00′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’00′,1,0))) d_0,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’01′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’01′,1,0))) d_1,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’02′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’02′,1,0))) d_2,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’03′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’03′,1,0))) d_3,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’04′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’04′,1,0))) d_4,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’05′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’05′,1,0))) d_5,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’06′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’06′,1,0))) d_6,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’07′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’07′,1,0))) d_7,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’08′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’08′,1,0))) d_5,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’09′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’09′,1,0))) d_9,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’10′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’10′,1,0))) d_10,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’11′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’11′,1,0))) d_11,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’12′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’12′,1,0))) d_12,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’13′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’13′,1,0))) d_13,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’14′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’14′,1,0))) d_14,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’15′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’15′,1,0))) d_15,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’16′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’16′,1,0))) d_16,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’17′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’17′,1,0))) d_17,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’18′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’18′,1,0))) d_18,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’19′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’19′,1,0))) d_19,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’20′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’20′,1,0))) d_20,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’21′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’21′,1,0))) d_21,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’22′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’22′,1,0))) d_22,
decode(sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’23′,1,0)),0,’-',sum(decode(substr(to_char(FIRST_TIME,’HH24′),1,2),’23′,1,0))) d_23,
count(trunc(FIRST_TIME)) Total
from v$log_history
group by to_char(FIRST_TIME,’DY, DD-MON-YYYY’)
order by to_date(substr(to_char(FIRST_TIME,’DY, DD-MON-YYYY’),5,15) )
/
Ttitle off
How to check for LOGGING/NOLOGGING objects in the DB:
Two example methods of querying the database for this information:
select owner , table_name, index_name
from dba_indexes
where logging=’NO’;
select tablespace_name, logging
from dba_tablespaces/
Kind Regards,
Francisco Munoz Alvarez
