Expert Oracle Exadata - Parent Directory

CHAPTER 10 EXADATA WAIT EVENTScolumns to the requesting process. The process then requests the next AU and the entire routine isrepeated until all the data has been scanned. So this event will occur repeatedly in a large scan.■ Note: Column Projection is one of the major optimizations provided by Smart Scans. The feature is slightlymisunderstood. It does not pass only columns in the select list back to the database servers; it also passes backsome columns from the WHERE clause. Older versions of cellsrv passed all columns specified in a WHERE clauseback to the database tier. Later versions have corrected this behavior to include only columns that are involved injoin predicates.Here’s a portion of a 10046 trace file showing some of the events. The query generating this trace filedid a full table scan which was performed via the direct read mechanism. (Note that we’ve shortenedsome of the lines to get them to fit, primarily by stripping off the time values):PARSING IN CURSOR #2 len=32 dep=0 uid=0 oct=3 lid=0 hv=123 ad='196' sqlid='162wjnvwyybhn'select sum(pk_col) from kso.skewEND OF STMTPARSE #2:c=2000,e=2424,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=1,plh=568322376EXEC #2:c=0,e=34,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,plh=568322376WAIT #2: nam='SQL*Net message to client' ela= 3 driver id=1650815232 #bytes=1 p3=0 obj#=-1WAIT #2: nam='ges message buffer allocation' ela= 2 pool=0 request=1 allocated=0 obj#=-1WAIT #2: nam='KJC: Wait for msg sends to complete' ela= 10 msg=6674450368 dest|rcvr=65536WAIT #2: nam='reliable message' ela= 1107 channel context=6712270872 channel handle=66967991WAIT #2: nam='ges message buffer allocation' ela= 1 pool=0 request=1 allocated=0 obj#=-1WAIT #2: nam='enq: KO - fast object checkpoint' ela= 104 name|mode=126 2=65575 0=1 obj#=-1WAIT #2: nam='ges message buffer allocation' ela= 1 pool=0 request=1 allocated=0 obj#=-1WAIT #2: nam='enq: KO - fast object checkpoint' ela= 103 name|mode=126 2=65575 0=2 obj#=-1WAIT #2: nam='cell smart table scan' ela= 162 cellhash#=2133459483 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 244 cellhash#=379339958 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 181 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 1285 cellhash#=2133459483 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 1327 cellhash#=379339958 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 1310 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 19755 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 39 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 24 cellhash#=2133459483 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 847 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 44 cellhash#=2133459483 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 674 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 32 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 39 cellhash#=2133459483 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 928 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 37 cellhash#=3176594409 p2=0 p3=0 obj#=66849WAIT #2: nam='cell smart table scan' ela= 97 cellhash#=379339958 p2=0 p3=0 obj#=66849This portion of the trace file also shows the enq: KO - fast object checkpoint event, which is usedto ensure that any dirty blocks for the scanned object are flushed to disk prior to beginning the scan. By324