Expert Oracle Exadata - Parent Directory

CHAPTER 10 EXADATA WAIT EVENTSTABLE ACCESS BY LOCAL INDEX ROWID 1428TABLE ACCESS STORAGE FULL 5046TABLE ACCESS STORAGE SAMPLE 916ParametersThe cell multiblock physical read event also provides more information than most cell events. Theparameters in the following list allow you to tell which object was read and identifies the disk and cellwhere the blocks were stored. The total bytes passed should be a multiple of the block size.P1 - Cell hash numberP2 - Disk hash numberP3 - Total bytes passed during read operationobj# - The object number of the object being readcell list of blocks physical readThis event is a replacement for the db file parallel read event. It appears that the developers took theopportunity to rename some of the events that are related to disk operations, and this is one of thoseevents. The new name is actually much more descriptive than the previous name, since the wait eventhas nothing whatsoever to do with parallel query or parallel DML.Event MeaningThis event is used for a multi-block read of noncontiguous blocks. This is more effective with async I/O,which is enabled on Exadata by default. This event can be provoked by several operations. The mostcommon are Index Range Scans, Index Unique Scans and Table Access By Index Rowid. The mostcommon reason for the event is index pre-fetching. Here is the output of a query that shows theoperations that resulted in this wait event on an active production system:SYS@EXDB1> select event, operation, count(*) from (2 select sql_id, event, sql_plan_operation||' '||sql_plan_options operation3 from DBA_HIST_ACTIVE_SESS_HISTORY4 where event like 'cell list%')5 group by operation, event6 order by 1,2,37 /EVENT OPERATION COUNT(*)----------------------------------- ---------------------------------------- --------cell list of blocks physical read 2INDEX RANGE SCAN 156INDEX STORAGE FAST FULL SCAN 1INDEX UNIQUE SCAN 66TABLE ACCESS BY GLOBAL INDEX ROWID 90TABLE ACCESS BY INDEX ROWID 1273TABLE ACCESS BY LOCAL INDEX ROWID 2593331