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Redo Transport Compression in a Data Guard Environment (文档 ID 729551.1) |
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In this Document
APPLIES TO:
Oracle Database -
Enterprise Edition - Version 11.1.0.6 to 11.2.0.3 [Release 11.1 to 11.2] PURPOSE
Oracle Database 11g has the ability to compress redo as it is
transmitted over a network by Data Guard Redo Transport Services. · Improve data protection by reducing redo transport lag · Reduce network utilization · Provide faster redo gap resolution · Reduce redo transfer time Redo transport compression is a feature of the Oracle Advanced Compression option. You must purchase a license for this option before using the redo transport compression feature. Compression of redo transport for versions prior to Oracle Database 11g Release 1 can be accomplished using third party WAN accelerators, such as those available from Cisco, Riverbed, F5, and other vendors. SCOPE Compression is most beneficial in achieving recovery point objectives (RPO) when used over low bandwidth networks. As a general statement, as network bandwidth increases, the RPO benefit is reduced. Compressing redo in a Data Guard environment is particularly beneficial if:
CPU consumption will increase in higher network bandwidth
environments since potentially a larger percentage of time is spent
compressing redo compared to transmitting redo. For example, gap resolution
testing showed that with OC1 (51.8 Mbits/sec) and T3 (44.7 Mbits/sec) networks,
50% of one CPU was consumed per ARCH process during the compression
operation, while with a 100Mbits network an entire CPU was consumed per ARCH
process. DETAILS From Oracle Database 11g Release 2 onward, setting the COMPRESSION attribute of the redo transport destination will compress redo transmitted by all Data Guard transport methods (SYNC, ASYNC, ARCH), including redo transmitted to resolve archive log gaps, and all Data Guard protection modes (Maximum Protection, Maximum Availability, and Maximum Performance). In Oracle Database 11g Release 1, setting the COMPRESSION attribute of the redo transport destination will only compress redo transmitted to resolve an archive log gap. Oracle also supports compression of ASYNC and ARCH redo transport (Maximum Performance) by using a hidden parameter in conjunction with enabling the COMPRESSION attribute as documented below. Enabling Data Guard Redo Transport Compression To enable compression, set the COMPRESSION attribute of the redo transport destination to ENABLE. For example: LOG_ARCHIVE_DEST_2='SERVICE=boston COMPRESSION=ENABLE DB_UNIQUE_NAME=boston'
DGMGRL> EDIT DATABASE 'boston' SET PROPERTY 'RedoCompression' = ENABLE;
Test Results and Other Guidance Oracle MAA testing showed that with a redo compression ratio of 35% or more, redo transmission time was reduced by 15-35%. Network Throughput
In addition, Oracle MAA testing showed:
Enabling Data Guard Redo Transport Compression for ASYNC when using Oracle Database 11g Release 1 To enable compression when using ASYNC or ARCH redo transport mode and Oracle Database 11g Release 1, set the COMPRESSION attribute of the redo transport destination to ENABLE, and set the initialization parameter _REDO_TRANSPORT_COMPRESS_ALL to TRUE (this initialization parameter is not needed from Oracle Database 11g Release 2 onward). For example:
LOG_ARCHIVE_DEST_2='SERVICE=boston ASYNC COMPRESSION=ENABLE
DB_UNIQUE_NAME=boston'
DGMGRL> EDIT DATABASE 'boston' SET PROPERTY 'RedoCompression' = ENABLE;
How to estimate the compression ratio that can be achieved:
Data Guard redo transport compression uses the same zlib
compression engine at level 1 as gzip -1. To estimate the compression ratio
you can achieve using Data Guard redo transport compression, first compress
an archived redo log file with gzip:
For more details please check also
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