Expert Oracle Exadata - Parent Directory

CHAPTER 5 EXADATA SMART FLASH CACHESYS@EXDB1> select avg(pk_col) from kso.skew3 where col1 > 1;AVG(PK_COL)-----------16053318.5Elapsed: 00:00:27.90SYS@EXDB1> @mystatsEnter value for name: cell flash%NAMEVALUE---------------------------------------------------------- ---------------cell flash cache read hits 45225Elapsed: 00:00:00.01In the preceding example you can see that the Smart Scan is faster when the CELL_FLASH_CACHEstorage clause attribute is set to KEEP and more importantly, that a large number of “cell flash cache readhits” are generated in that case. When the CELL_FLASH_CACHE attribute is set to DEFAULT, the query isslower and no “cell flash cache read hits” are generated.How ESFC is CreatedStorage configuration is covered in detail in Chapter 8, but the basic commands for creating andmanaging flash cache will be covered briefly in this section as well. The cache is created and managedusing the cellcli utility on each storage server (the cellcli command syntax is covered in detail inAppendix A). Alternatively, the dcli utility, which replicates commands across multiple storage cells, canbe used. The command to create the cache is CREATE FLASHCACHE. Here’s an example.CellCLI> create flashcache all size=300gFlash cache cell03_FLASHCACHE successfully createdThis form of the command tells the storage software to spread the cache across all the FMods on allthe flash cards. In this case, the size parameter was used to specify that the entire cache should occupyonly 300G, leaving roughly 65G available for use as a flash disk. To use all available space for flash cache,simply leave off the size parameter.CellCLI> create flashcache allFlash cache cell03_FLASHCACHE successfully createdThis command uses all available storage on all available flash cards. Note that the flash cache isautomatically assigned a name that includes the name of the storage cell. To see the size of theflashcache you can issue the LIST FLASHCACHE DETAIL command:CellCLI> list flashcache detailname:cell03_FLASHCACHEcellDisk: FD_15_cell03,FD_02_cell03,FD_14_cell03,FD_10_cell03,FD_01_cell03,FD_13_cell03,FD_12_cell03,FD_08_cell03,FD_07_cell03,FD_11_cell03,FD_09_cell03,FD_05_cell03,FD_06_cell03,FD_04_cell03,FD_03_cell03,FD_00_cell03creationTime:2010-11-07T19:45:32-06:00degradedCelldisks:132