Oracle Database 11 g - Online Public Access Catalog

424 CHAPTER 10 ■ DATA GUARDSQL> create table docs_dr (doc_id number, name varchar2(4000), lob_content blob);Table created.SQL> insert into docs_dr (doc_id, name) values(1, 'Oracle Maximum Availability Architecture');1 row created.SQL> commit;Commit complete.Since you do not apply archivelogs while the database is in standby mode, over time thesnapshot standby database deviates from the primary database. The duration a snapshotstandby database can continue in this mode is dependent on the company’s recovery pointobjectives (RPOs) and recovery time objectives (RTOs). The snapshot standby database can beideal for short testing scenarios such as a load test to confirm that a schema or an applicationpatch or a major upgrade will cause performance issues. The good news is that even though thedatabase continues to be in snapshot standby mode, you can continue to ship archivelogsfrom the primary database to the disaster recovery site. The DBA should know how manyarchivelogs can be applied per hour, and based on the RPO/RTO, they will know how long theycan continue in the snapshot standby mode without compromising the business’s RPO/RTO.There are two factors to consider while the physical database is in the snapshot standby databasemode:• The number of archivelogs generated from the primary database source• The amount of data updated while the standby database is in updatable modeBusinesses can reap the benefits from a temporary snapshot of the primary database andjustify the return on investment from the amount of money spent on disaster recovery licenses.Behind the scenes, Oracle creates an implicit guaranteed restore point on the physicalstandby database prior to converting the snapshot standby database. GAP detection and resolutioncontinue as usual while the database is in snapshot standby mode. Once the database isready to be flashed back to the point prior to opening the database in updatable mode, a guaranteedrestore point is used to flash back a snapshot standby to the point in time prior toconverting the physical standby database to the snapshot standby database. By default, theguaranteed restore point is named with the SNAPSHOT_STANDBY_REQUIRED_ prefix appended bythe system date. You can query the V$RESTORE_POINT view to determine the name of therestore point, as revealed here:SQL> select name, storage_size from v$restore_point;NAMESTORAGE_SIZE------------------------------------ ------------------------SNAPSHOT_STANDBY_REQUIRED_05/01/2007 8192000You can accomplish the equivalent of the snapshot standby database in Oracle Database10g Release 2 Data Guard using the guaranteed restore points. The only caveat is that the DBA