What the heck is “snapshot standby”?

I was just reviewing Note:565535.1 Flashback Database Best Practices & Performance and came across the following paragraph under the title of “Measuring Impact of turning Flashback Database ON / Analyzing the Performance Impact“:

If you’re on RDBMS release 11g and have a physical standby, then you can enable flashback database on your physical standby and then convert it to a snapshot standby (this can also be done in 10.2 with a manual snapshot standby, but no redo is received and applied as in the 11g Snapshot Standby. See Dell 10g Snapshot Standby – Dell 10g Snapshot Standby). Then when you run a workload against the snapshot standby it will be with flashback database logging enabled.

So what the heck is “snapshot standby”?

Essentially it allows you to convert your 11g physical standy to a “Snapshot standby” so that you can “Make changes to the Primary and the the Snapshot standby in some common tables” and then “Convert the Snapshot standby back to a Physical standby”. Makes sense? NO? OK, I know, how about this:

  • A snapshot standby database is a fully updateable standby database created by converting a physical standby database into a snapshot standby database.
  • A snapshot standby database receives and archives, but does not apply, redo data from a primary database. The redo data received from the primary database is applied once a snapshot standby database is converted back into a physical standby database, after discarding all local updates to the snapshot standby database.
  • A snapshot standby can be created from Enterprise Manager, the Data Guard Broker command line interface (DGMGRL) or from SQL*Plus.

Better? YES. This is probably THE reason to go 11g if you haven’t already. Basically you get an instant REPORTING/TEST server without loosing your Physical Standby database. See: Using Snapshot Standby for an example.

June 15, 2009

Posted In: Data Guard

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