Expert Oracle Exadata - Parent Directory

CHAPTER 13 MIGRATING TO EXADATAsince the last level 0 backup by flipping a bit in a small bitmap file. This means that when you take anincremental level 1 backup, Oracle doesn’t have to scan every block in the database to see which oneshave changed. I’ve seen this reduce an incremental backup of a 13T data warehouse from 9 hours to justover 15 minutes. To see if block change tracking is active execute the following query in SQL*Plus:SQL> SELECT status FROM v$block_change_tracking;STATUS----------DISABLEDYou do not have to shut down the database to activate block change tracking. It can be done at anytime. To turn on block change tracking, execute the following command:SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;Database altered.By default the block change tracking file is created in the db_create_file_dest location. If thisparameter is not set, you will need to set it or specify the file name for the block change tracking file, likethis:ALTER DATABASE ENABLE BLOCK CHANGE TRACKINGUSING FILE '/u01/app/oracle/product/11.2.0/dbhome_1/dbs/TEST_bct.ct' {REUSE};Post-migration tasks are necessary to convert your single-instance Exadata database to a multiinstanceRAC database. Converting a single-instance database to RAC will be covered at the end of the“Physical Migration” section of this chapter. Once the database is recovered and running on Exadata,you should make a full database backup. Assuming the database is running in Archivelog mode, you cando this after the database is back online and servicing end users and applications.When to Use Backup and RestoreExecuting a simple database backup and recovery using RMAN is something every DBA should be ableto do in their sleep. This makes the Backup and Restore a very attractive strategy. It is best suited forOLTP databases that don’t require partitioning and HCC compression. It is also suitable for DWdatabases that already run on a little-endian, 64-bit platform, post-migration steps notwithstanding.What to Watch Out for when Considering the Backup and Restore StrategyIncremental backup and restore does not support platform conversion. If this is a requirement, youmight be better off using the TTS migration strategy or revisiting some of the logical migration strategieswe’ve discussed in this chapter. Objects will need to be rebuilt after migration to take advantage ofExadata storage features such as HCC.Transportable Tablespaces (and XTTS)Transportable tablespaces (TTS) can be used to migrate subsets of the source database to Exadata. To dothis you will need a running database on Exadata to host these subsets of your database. We oftendescribe TTS as a sort of “Prune and Graft” procedure. This method allows a set of tablespaces to becopied from a source database, and installed into a live target database. The TTS process is fairly simplebut there are a few things you will need to be aware of before beginning.455