redo log file 優化

redo log file 優化

本文主要介紹redo log file大小的優化。
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Oracle Environment=>11.2.0.4.0 rac on two nodes
OS Environment=>redhat 6.3 (64bit)
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總體思路如下：
1.redo log file現狀監控
2.redo log file切換總覽
3.redo log file優化
3.1 官方建議20分鐘切換一次
3.2 MTTR角度優化

1.redo log file現狀監控
#redo log files 現狀監控#

set linesize 300
column REDOLOG_FILE_NAME format a50
SELECT
a.GROUP#,
a.THREAD#,
a.SEQUENCE#,
a.ARCHIVED,
a.STATUS,
b.MEMBER AS REDOLOG_FILE_NAME,
(a.BYTES/1024/1024) AS SIZE_MB
FROM v$log a
JOIN v$logfile b ON a.Group#=b.Group#
ORDER BY a.GROUP# ASC;

GROUP# THREAD# SEQUENCE# ARC STATUS REDOLOG_FILE_NAME SIZE_MB
---------- ---------- ---------- --- ---------------- -------------------------------------------------- ----------
1 1 4965 YES ACTIVE +DATA/BMCTEST/redo01.log 50
2 1 4966 NO CURRENT +DATA/BMCTEST/redo02.log 50
3 2 3405 YES INACTIVE +DATA/BMCTEST/redo03.log 50
4 2 3406 NO CURRENT +DATA/BMCTEST/redo04.log 50

2.redo log file切換總覽
#redo log files檢視指令碼#
select
Start_Date,
Start_Time,
Num_Logs,
Round(Num_Logs * (Vl.Bytes / (1024 * 1024)), 2) AS Mbytes,
Vdb.NAME AS Dbname
FROM
(SELECT To_Char(Vlh.First_Time, 'YYYY-MM-DD') AS Start_Date, To_Char(Vlh.First_Time, 'HH24') || ':00' AS Start_Time,
COUNT(Vlh.Thread#) Num_Logs
FROM
V$log_History Vlh
GROUP BY
To_Char(Vlh.First_Time, 'YYYY-MM-DD'),
To_Char(Vlh.First_Time, 'HH24') || ':00') Log_Hist,
V$log Vl,
V$database Vdb
WHERE
Vl.Group# = 1
ORDER BY
Log_Hist.Start_Date,
Log_Hist.Start_Time;

...........
2015-05-29 10:00 88 44000 BMCTEST
2015-05-29 11:00 22 11000 BMCTEST
2015-05-29 12:00 1 500 BMCTEST
2015-05-30 00:00 1 500 BMCTEST
2015-06-01 02:00 1 500 BMCTEST
2015-06-01 22:00 1 500 BMCTEST
2015-06-03 11:00 64 32000 BMCTEST

START_DATE START NUM_LOGS MBYTES DBNAME
---------- ----- ---------- ---------- ---------
2015-06-03 12:00 157 78500 BMCTEST
2015-06-03 13:00 49 24500 BMCTEST
2015-06-03 14:00 9 4500 BMCTEST
2015-06-03 15:00 17 8500 BMCTEST

參考：http://www.dba-oracle.com/m_redo_size.htm

3.redo log file優化
3.1 官方建議20分鐘切換一次

一般優化指導方針：

當前 10分鐘/切換 200M =>優化目標 20分鐘/切換=>200M*2=400M

#從效能切換角度，10分鐘切換一次，估算redo log files大小#（從0點到23點59分）#

SELECT
(SELECT ROUND(AVG(BYTES) / 1024 / 1024, 2) FROM V$LOG) AS "Redo size (MB)",
ROUND((10 / AVERAGE_PERIOD) * (SELECT AVG(BYTES)
FROM V$LOG) / 1024 / 1024, 2) AS "Recommended Size (MB)"
FROM (SELECT AVG((NEXT_TIME - FIRST_TIME) * 24 * 60) AS AVERAGE_PERIOD
FROM V$ARCHIVED_LOG
WHERE FIRST_TIME > SYSDATE - 3
AND TO_CHAR(FIRST_TIME, 'HH24:MI') BETWEEN
'00:00' AND '23:59');

Redo size (MB) Recommended Size (MB)
-------------- ---------------------
500 514.53

3.2 MTTR角度優化

#從恢復時間角度，MTTR角度#

SQL> ALTER SYSTEM SET FAST_START_MTTR_TARGET=60; #秒

System altered.

SQL> SELECT OPTIMAL_LOGFILE_SIZE FROM V$INSTANCE_RECOVERY;

OPTIMAL_LOGFILE_SIZE
--------------------
880（M）

參考：http://www.gokhanatil.com/2009/08/optimum-size-of-the-online-redo-log-files.html

總結：效能優化，儘量“庫存”更多的監控，分析指令碼。

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redo log file 優化

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