Enabling Redo Log Transport Compression with active dataguard

0racle 11g release 1后提供了redo 日志传输压缩的功能，可以快速的解决归档日志gap的问题，可以在ASYNC/MaxPerformance redo transport模式下启用压缩，11.2.0.1版本以后也可以扩展到MaxProtection, MaxAvailability模式；本文介绍oracle 11g active data guard环境下(MAXIMUM AVAILABILITY)对redo传输的压缩； redo 日志传输压缩适用于redo切换快，带宽小且CPU强劲的data guard环境下！

一：查看日志传输的延时情况

[root@db1 ~]# su - oracle
[oracle@db1 ~]$ sqlplus /nolog
SQL*Plus: Release 11.2.0.3.0 Production on Wed Nov 28 09:42:48 2012
Copyright (c) 1982, 2011, Oracle.  All rights reserved.

SQL> conn /as sysdba
Connected.

SQL> select protection_mode,protection_level,database_role from v$database;

PROTECTION_MODE      PROTECTION_LEVEL     DATABASE_ROLE
-------------------- -------------------- ----------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY PRIMARY

SQL> SELECT max(DURATION) FROM V$REDO_DEST_RESP_HISTOGRAM WHERE DEST_ID=2 AND FREQUENCY>1;

MAX(DURATION)
-------------
            7

SQL> SELECT min(DURATION) FROM V$REDO_DEST_RESP_HISTOGRAM WHERE DEST_ID=2 AND FREQUENCY>1;

MIN(DURATION)
-------------
            1

SQL>  SELECT FREQUENCY, DURATION FROM V$REDO_DEST_RESP_HISTOGRAM WHERE DEST_ID=2 AND FREQUENCY>1;
 FREQUENCY   DURATION
---------- ----------
      4018          1
        13          2
        11          3
        11          4
         3          5
         2          6
         2          7
7 rows selected.

二：修改隐含参数_REDO_TRANSPORT_COMPRESS_ALL，重启实例

SQL> col  parameter for a20
SQL> col value for a20

SQL> select * from v$option where parameter ='Advanced Compression';

PARAMETER            VALUE
-------------------- --------------------
Advanced Compression TRUE

SQL> alter system set "_REDO_TRANSPORT_COMPRESS_ALL"=TRUE SCOPE=SPFILE;
System altered.

SQL> show parameter COMPRESS;

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1536602112 bytes
Fixed Size                  2228624 bytes
Variable Size            1174408816 bytes
Database Buffers          352321536 bytes
Redo Buffers                7643136 bytes
Database mounted.
Database opened.

SQL> show parameter COMPRESS;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------
_redo_transport_compress_all         boolean     TRUE

三：修改log_archive_dest_2参数

SQL> show parameter log_archive_dest_2;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2                   string      SERVICE=db2 lgwr sync valid_fo
                                                 r=(online_logfiles,primary_role
                                                 ) db_unique_name=db2

SQL> alter system set log_archive_dest_2='SERVICE=db2 lgwr sync valid_for=(online_logfiles,primary_role) compression=enable db_unique_name=db2';
System altered.

SQL> show parameter log_archive_dest_2

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2                   string      SERVICE=db2 lgwr sync valid_fo
                                                 r=(online_logfiles,primary_rol
                                                 e) compression=enable db_uniqu
                                                 e_name=db2

四：验证压缩

SQL> select DEST_ID,COMPRESSION  from v$archive_dest where dest_id=2;

   DEST_ID COMPRES
---------- -------
         2 ENABLE


SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     196
Next log sequence to archive   198
Current log sequence           198

压缩采用gzip 1方式进行，压缩及解压缩oracle全自动进行，压缩的比率到了79%：
[oracle@db1 2012_11_28]$ gzip -1  o1_mf_1_198_8cbvxpm1_.arc
[oracle@db1 2012_11_28]$ gzip --list o1_mf_1_198_8cbvxpm1_.arc.gz
         compressed        uncompressed  ratio uncompressed_name
             139090              671744  79.3% o1_mf_1_198_8cbvxpm1_.arc

参考文章:
http://oraclehandson.wordpress.com/2011/01/07/enabling-redo-log-transport-compression/ (请×××访问！)
http://docs.oracle.com/cd/B28359_01/server.111/b28294/log_transport.htm#BABEBHHB
https://support.oracle.com/epmos/faces/DocumentDisplay?_afrLoop=325669420448759&id=729551.1&_afrWindowMode=0&_adf.ctrl-state=7uubfwzms_4