Expert Oracle Exadata - Parent Directory

CHAPTER 3 HYBRID COLUMNAR COMPRESSIONOWNER SEGMENT_NAME TOTALSIZE_MEGS COMPRESS_FOR-------------------- ------------------------------ -------------- ------------KSO SKEW_OLTP 903.1 OLTP--------------sum 903.11 row selected.SYS@SANDBOX1> @comp_ratioEnter value for original_size: 1460.3Enter value for owner: KSOEnter value for table_name: SKEW%Enter value for type:OWNER SEGMENT_NAME TYPE TOTALSIZE_MEGS COMPRESSION_RATIO---------- -------------------- ------------------ -------------- -----------------KSO SKEW TABLE 1,460.3 1.0KSO SKEW_HCC3 TABLE 916.0 1.6KSO SKEW_OLTP TABLE 903.1 1.6--------------sum 3,279.43 rows selected.This output shows that updating all the records in an HCC ARCHIVE LOW table expanded it to aslightly larger footprint than an OLTP-compressed (via direct path load) version of the same table.Interestingly enough, the update statement spent most of its time waiting on BUFFER BUSY WAITS.Apparently there is not a specific wait event for when a process is waiting while a block is beingcompressed. Here is the complete set of events that the update statement waited on (from a 10046 tracefile processed with tkprof), along with per-second session statistics (both from one of the parallel slaveprocesses):Elapsed times include waiting on following events:Event waited on Times Max. Wait Total Waited---------------------------------------- Waited ---------- ------------cursor: pin S wait on X 1 0.01 0.01PX Deq: Execution Msg 16 67.43 68.15cell multiblock physical read 14 0.00 0.02resmgr:cpu quantum 90 0.01 0.14buffer busy waits 2077 3.54 139.84latch: cache buffers chains 2068 0.34 6.75enq: TX - contention 66 0.27 0.33enq: HW - contention 142 1.55 16.56latch: redo allocation 361 0.25 1.51global enqueue expand wait 19 0.00 0.00gc current multi block request 67 0.00 0.03KJC: Wait for msg sends to complete 16 0.00 0.00log buffer space 230 0.28 12.44latch: enqueue hash chains 28 0.00 0.01latch: ges resource hash list 20 0.01 0.05log file switch completion 5 0.30 0.88enq: FB - contention 61 0.03 0.1285