DG 链路开启redo压缩传输，节约链路带宽

主库参数设置：

LOG_ARCHIVE_DEST_2='SERVICE=<SERVICE_NAME> COMPRESSION=ENABLE DB_UNIQUE_NAME=<DB_UNIQUE_NAME>'

redo压缩率可达到35%或更高，取决于主库性能

可以按以下方法测试压缩率：

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:

$ gzip -1 <archive redo logfile>.arc

Then use the gzip --list option to explicitly display the compression ratio:

$ gzip --list <archive redo logfile.arc>.gz

Note: Use gzip version 1.3.3 or later. Refer to www.gzip.org for the latest information on gzip.

参考文章：

Redo Transport Compression in a Data Guard Environment (Doc ID 729551.1)