Expert Oracle Exadata - Parent Directory

CHAPTER 3 HYBRID COLUMNAR COMPRESSIONCpu(s): 97.3%us, 0.4%sy, 0.0%ni, 2.2%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%stMem: 74027752k total, 35141864k used, 38885888k free, 192548k buffersSwap: 16771852k total, 0k used, 16771852k free, 30645208k cachedPID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND21657 oracle 25 0 10.1g 111m 72m R 99.1 0.2 5:20.16 ora_p001_SANDBOX221663 oracle 25 0 10.1g 113m 80m R 99.1 0.2 5:11.11 ora_p004_SANDBOX226481 oracle 25 0 10.1g 89m 54m R 99.1 0.1 3:07.37 ora_p008_SANDBOX226496 oracle 25 0 10.1g 89m 54m R 99.1 0.1 3:06.88 ora_p015_SANDBOX221667 oracle 25 0 10.1g 110m 73m R 98.5 0.2 5:16.09 ora_p006_SANDBOX226483 oracle 25 0 10.1g 89m 53m R 98.5 0.1 3:06.63 ora_p009_SANDBOX226488 oracle 25 0 10.1g 90m 52m R 98.5 0.1 3:08.71 ora_p011_SANDBOX226485 oracle 25 0 10.1g 90m 54m R 97.9 0.1 3:04.54 ora_p010_SANDBOX226490 oracle 25 0 10.1g 90m 54m R 97.9 0.1 3:04.46 ora_p012_SANDBOX221655 oracle 25 0 10.1g 105m 70m R 97.3 0.1 5:13.22 ora_p000_SANDBOX226494 oracle 25 0 10.1g 89m 52m R 97.3 0.1 3:03.42 ora_p014_SANDBOX221661 oracle 25 0 10.1g 106m 73m R 95.4 0.1 5:12.65 ora_p003_SANDBOX226492 oracle 25 0 10.1g 89m 54m R 95.4 0.1 3:08.13 ora_p013_SANDBOX221659 oracle 25 0 10.1g 114m 79m R 94.8 0.2 5:13.42 ora_p002_SANDBOX221669 oracle 25 0 10.1g 107m 72m R 90.5 0.1 5:10.19 ora_p007_SANDBOX221665 oracle 25 0 10.1g 107m 67m R 86.2 0.1 5:18.80 ora_p005_SANDBOX2Query PerformanceOf course, load time is not the only performance metric of interest. Query time is more critical than loadtime for most systems since the data is only loaded once but queried many times. Query performance isa mixed bag when it comes to compression. Depending on the type of query, compression can eitherspeed it up or slow it down. Decompression certainly adds overhead in the way of additional CPU usage,but for queries that are bottlenecked on disk access, reducing the number of blocks that must be readcan often offset and in many cases more than make up for the additional overhead. Keep in mind thatdepending on the access mechanism used, the decompression can be done on either the storage cells(smart scans) or on the database nodes. Here’s an example of running a CPU-intensive procedure:SYS@SANDBOX1> !cat gather_table_stats.sqlbegindbms_stats.gather_table_stats('&owner','&table_name',degree => 32,method_opt => 'for all columns size 1');end;/SYS@SANDBOX1> @gather_table_statsEnter value for owner: ACOLVINEnter value for table_name: SKEW3PL/SQL procedure successfully completed.Elapsed: 00:00:12.14SYS@SANDBOX1> @gather_table_statsEnter value for owner: KSO78