Expert Oracle Exadata - Parent Directory

CHAPTER 6 MAKING PCBSSQL_ID AVG_ETIME PX OFFLOAD IO_SAVED% SQL_TEXT------------- ---------- --- ------- --------- ------------------------------05cq2hb1r37tr .47 8 No .00 select avg(pk_col) fromkso.skew a where col1 > 005cq2hb1r37tr .58 8 Yes 59.82 select avg(pk_col) fromkso.skew a where col1 > 02 rows selected.Notice that with In-memory Parallel Execution disabled, the statistics show that the number ofphysical reads increased by roughly the number of blocks in the table, as expected. Notice also that thefsx.sql script shows that there is now a new cursor in the shared pool that was executed with eightparallel slaves, but that was offloaded to the storage tier. This is an important point. In-memory ParallelExecution disables the optimizations that Exadata provides via Smart Scans. That should be obvioussince the disk I/O was eliminated by the In-memory Parallel Execution feature, but it is the main reasonthat we believe this feature will not be as useful on the Exadata platform as on other platforms.As a final demonstration, we’ll show a very selective query that benefits more from Offloading thanit does from In-memory Parallel Execution.SYS@EXDB1> @parmsEnter value for parameter: para%cacheEnter value for isset:Enter value for show_hidden: YNAME VALUE ISDEFAUL---------------------------------------- -------------------- --------_parallel_cluster_cache_pct 80 TRUE_parallel_cluster_cache_policy ADAPTIVE TRUE2 rows selected.SYS@EXDB1> -- In-memory Paraellel Execution is offSYS@EXDB1>SYS@EXDB1> @flush_poolSystem altered.SYS@EXDB1> set timing onSYS@EXDB1> select count(*) from kso.skew where col1 is null;COUNT(*)----------41 row selected.Elapsed: 00:00:00.26SYS@EXDB1> alter system set "_parallel_cluster_cache_policy"=cached;System altered.Elapsed: 00:00:00.01172