Find the cause of High redo generation in Oracle

Check the high redo generation timing and cause in Oracle

We can also check from the current scenario which session or transaction is generating more logs from currently connected sessions:

-- Check the session caused high block change from the following query:
SELECT s.sid, s.serial#, s.username, s.program,
 i.block_changes
FROM v$session s, v$sess_io i
WHERE s.sid = i.sid
ORDER BY 5 desc;

--Check the transaction which caused high block change:
SELECT s.sid, s.serial#, s.username, s.program, 
t.used_ublk, t.used_urec
FROM v$session s, v$transaction t
WHERE s.taddr = t.addr
ORDER BY 5 desc, 6 desc;

From history we need to take help form AWR repository tables:

Check the timing for high redo generation in Oracle

SELECT * FROM (
SELECT * FROM (
SELECT TO_CHAR(FIRST_TIME, 'DD/MM') AS "DAY"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '00', 1, 0)), '999') "00:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '01', 1, 0)), '999') "01:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '02', 1, 0)), '999') "02:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '03', 1, 0)), '999') "03:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '04', 1, 0)), '999') "04:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '05', 1, 0)), '999') "05:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '06', 1, 0)), '999') "06:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '07', 1, 0)), '999') "07:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '08', 1, 0)), '999') "08:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '09', 1, 0)), '999') "09:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '10', 1, 0)), '999') "10:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '11', 1, 0)), '999') "11:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '12', 1, 0)), '999') "12:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '13', 1, 0)), '999') "13:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '14', 1, 0)), '999') "14:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '15', 1, 0)), '999') "15:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '16', 1, 0)), '999') "16:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '17', 1, 0)), '999') "17:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '18', 1, 0)), '999') "18:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '19', 1, 0)), '999') "19:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '20', 1, 0)), '999') "20:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '21', 1, 0)), '999') "21:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '22', 1, 0)), '999') "22:00"
, TO_NUMBER(SUM(DECODE(TO_CHAR(FIRST_TIME, 'HH24'), '23', 1, 0)), '999') "23:00"
FROM V$LOG_HISTORY
WHERE extract(year FROM FIRST_TIME) = extract(year FROM sysdate)
GROUP BY TO_CHAR(FIRST_TIME, 'DD/MM')
) ORDER BY TO_DATE(extract(year FROM sysdate) || DAY, 'YYYY DD/MM') DESC
) WHERE ROWNUM < 8

From the above query, we find the timing at which the archive log is generated more. By using AWR tables, We find the object name which caused a high archive during that time.

SELECT to_char(begin_interval_time,'YY-MM-DD HH24') snap_time,
dhso.object_name,
sum(db_block_changes_delta) BLOCK_CHANGED
FROM dba_hist_seg_stat dhss,
dba_hist_seg_stat_obj dhso,
dba_hist_snapshot dhs
WHERE dhs.snap_id = dhss.snap_id
AND dhs.instance_number = dhss.instance_number
AND dhss.obj# = dhso.obj#
AND dhss.dataobj# = dhso.dataobj#
AND begin_interval_time BETWEEN to_date('22-11-18 11:00','YY-MM-DD HH24:MI') AND to_date('12-11-18 12:00','YY-MM-DD HH24:MI')
GROUP BY to_char(begin_interval_time,'YY-MM-DD HH24'),
dhso.object_name
HAVING sum(db_block_changes_delta) > 0
ORDER BY sum(db_block_changes_delta) desc ;

Find the SQL query which causing more archives with help of AWR tables as below:

You need to use the segment name from the above query and the timing from the first query.

SELECT to_char(begin_interval_time,'YYYY_MM_DD HH24') WHEN,
dbms_lob.substr(sql_text,4000,1) SQL,
dhss.instance_number INST_ID,
dhss.sql_id,
executions_delta exec_delta,
rows_processed_delta rows_proc_delta
FROM dba_hist_sqlstat dhss,
dba_hist_snapshot dhs,
dba_hist_sqltext dhst
WHERE upper(dhst.sql_text) LIKE '%<segment_name>%'
AND ltrim(upper(dhst.sql_text)) NOT LIKE 'SELECT%'
AND dhss.snap_id=dhs.snap_id
AND dhss.instance_number=dhs.instance_number
AND dhss.sql_id=dhst.sql_id
AND begin_interval_time BETWEEN to_date('22-11-18 11:00','YY-MM-DD HH24:MI') 
AND to_date('22-11-18 12:00','YY-MM-DD HH24:MI') 

Note: You need to have a license for AWR for using these tables.

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