0racle 11g release 1后提供了redo 日志傳輸壓縮的功能，可以快速的解決歸檔日志gap的問題，可以在ASYNC/MaxPerformance redo transport模式下啟用壓縮，11.2.0.1版本以后也可以擴展到MaxProtection, MaxAvailability模式；本文介紹oracle 11g active data guard環境下(MAXIMUM AVAILABILITY)對redo傳輸的壓縮； redo 日志傳輸壓縮適用于redo切換快，帶寬小且CPU強勁的data guard環境下！
一：查看日志傳輸的延時情況
[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$REDO_DEST_RESP_HISTOGRAM?WHERE?DEST_ID=2?AND?FREQUENCY>1; ??FREQUENCY???DURATION ?----------?---------- ???????4018??????????1 ?????????13??????????2 ?????????11??????????3 ?????????11??????????4 ??????????3??????????5 ??????????2??????????6 ??????????2??????????7 ?7?rows?selected.? 二：修改隱含參數_REDO_TRANSPORT_COMPRESS_ALL，重啟實例
SQL>?col??parameter?for?a20 ?SQL>?col?value?for?a20 ??SQL>?select?*?from?v$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_2參數
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：驗證壓縮
SQL>?select?DEST_ID,COMPRESSION??from?v$archive_dest?where?dest_id=2; ?????DEST_ID?COMPRES ?----------?------- ??????????2?ENABLE ???SQL>?archive?log?list; ?Database?log?mode??????????????Archive?Mode ?Automatic?archival?????????????Enabled ?Archive?destination????????????USE_DB_RECOVERY_FILE_DEST ?Oldest?online?log?sequence?????196 ?Next?log?sequence?to?archive???198 ?Current?log?sequence???????????198 ??壓縮采用gzip?1方式進行，壓縮及解壓縮oracle全自動進行，壓縮的比率到了79%： ?[oracle@db1?2012_11_28]$?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? 參考文章:
http://oraclehandson.wordpress.com/2011/01/07/enabling-redo-log-transport-compression/ (請***訪問！)
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
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