Oracle Database 11 g - Online Public Access Catalog

430 CHAPTER 10 ■ DATA GUARDwho have high-latency and low-bandwidth WAN networks. This compressed redo feature canbe turned on by enabling the log_archive_dest_1 parameter with the compression parameter.Compression becomes enabled only when a GAP exists and the standby database needs tocatch up to the primary database. When a GAP resolution is detected, the redo transport can beenabled to ship logs in compressed mode. This will reduce the network bandwidth. By default,the compression attribute is disabled and is optional. To enable compression of redo transport,you can use the alter system syntax:SQL> alter system set log_archive_dest_1 = 'SERVICE=DBA11GDR COMPRESSION=ENABLE';System altered.Alternatively, you can enable compression using Data Guard Broker by setting theRedoCompression property to enable. In the following example, the RedoCompression propertywill be set on both the primary and physical standby databases:DGMGRL> edit database 'dba11g' set property redocompression=enable;Property "redocompression" updatedOn the standby database, you can enable redo compression also:DGMGRL> edit database 'dba11gdr' set property redocompression=enable;Property "redocompression" updatedOnce you set compression, either through Data Guard Broker or by modifying the log_archive_dest_1 parameter, you can query the V$ARCHIVE_DEST view to confirm that redo logcompression is enabled, as shown here:SQL> select dest_name, compression from v$archive_dest;DEST_NAMECOMPRESSION-------------------- -----------LOG_ARCHIVE_DEST_1 ENABLERedo log compression can also be disabled by using the disable option with Data GuardBroker or by setting the log_archive_dest_1 initialization parameter. When adding a database tothe Data Guard configuration, Data Guard Broker will detect the archive destination compressionsetting and adjust the RedoCompression property.■Note Using network compression with Data Guard redo transport services requires a license for OracleAdvanced Compression.Usage of Histograms for the NET_TIMEOUT AttributesThe optional net_timeout parameter to the log_archive_dest_n initialization parameter allowsthe DBAs to specify the number of seconds the log writer process (LGWR) waits for a response