Data Guard — it’s real it’s Oracle, you know what you’ve got!
“Data Guard — it’s real it’s Oracle, you know what you’ve got!” said Joe Meeks (Director of High Availability Product Management at Oracle) in his closing statement during the Live Webcast presentation titled “Maximize Availability with Oracle Database 11g” held today.
The focus of this presentation was on “Active Data Guard Option” of Oracle 11g. In one sentence — Active Data Guard Option lets you open your Physical Standby database READ-Only all while redo-apply is taking place from primary. In contrast, in 10g, redo-apply halted when physical standby was opened READ-Only, the redo transportation was still taking place but it was not being applied in 10g. 11g bridges this gap and it does so very efficiently — as Joe Meeks said “With 11gR2 Active Data Guard – we are confident that latency is very low”.
Data Guard != ZERO Downtime because rolling upgrade still requires downtime. For example, according to Joe’s recollection of a major upgrade at UPS — their downtime going from 10g to 11g took ~ 4 minutes. To get ZERO downtime you must design your application around Oracle Streams.
In contrast to Data Guard, which uses media recovery (block by block), Oracle Streams are building logical change records using SQL. Steams are providing full featured replication features at your disposal, for example you can:
- replicate a subset of database
- perform transformations
- replicate across platforms
- setup multimaster replications
- replicate to a database and have it replicate different subsets of data out
Data Guard is simpler, one way replication — focused on DR using media recovery process (time tested process). Physical Standby is very horizontal, transparent to the storage and application.
PS: Active Data Guard is only available for Physical Standby (block by block changes) and it requires an additional license.