Expert Oracle Exadata - Parent Directory

CHAPTER 2 OFFLOADING / SMART SCANPREDICTION_PROBABILITYPREDICTION_SETV10R2 Oracle YESV10R2 Oracle NO6 rows selected.As you can see, some of the functions are offloadable and some are not. The ones that areoffloadable can be used by the storage cells for Predicate Filtering. Here’s an example query that shouldonly return records that meet the scoring requirement specified in the WHERE clause:select cust_idfrom customerswhere region = 'US'and prediction_probability(churnmod,'Y' using *) > 0.8;This optimization is designed to offload CPU usage as well as reduce the volume of data transferred.However, it is most beneficial in situations where it can reduce the data returned to the database tier,such as in the previous example.Non-Smart Scan OffloadingThere are a few optimizations that are not related to query processing. As these are not the focus of thischapter we will only touch on them briefly.Smart File CreationThis optimization has a somewhat misleading name. It really is an optimization designed to speed upblock initialization. Whenever blocks are allocated, the database must initialize them. This activityhappens when tablespaces are created, but it also occurs when files are extended for any number ofother reasons. On non-Exadata storage, these situations require the database server to format each blockand then write them back to disk. All that reading and writing causes a lot of traffic between the databaseservers and the storage cells. As you are now aware, eliminating traffic between the layers is a primarygoal of Exadata. So as you might imagine, this totally unnecessary traffic has been eliminated. Blocks areformatted by the storage cells themselves without having to send them to the database servers. Timespent waiting on this activity is recorded by the Smart File Creation wait event. This wait event and theoperations that invoke it are covered in more detail in Chapter 10.RMAN Incremental BackupsExadata speeds up incremental backups by increasing the granularity of block change tracking. On non-Exadata platforms, block changes are tracked for groups of blocks; on Exadata, changes are tracked forindividual blocks. This can significantly decrease the number of blocks that must be backed up, resultingin smaller backup sizes, less I/O bandwidth, and reduced time to complete incremental backups. Thisfeature can be disabled by setting the _DISABLE_CELL_OPTIMIZED_BACKUPS parameter to a value of TRUE.This optimization is covered in Chapter 9.RMAN RestoresThis optimization speeds up the file initialization portion when restoring from backup on a cell.Although restoring databases from backups is rare, this optimization can also help speed up cloning of44