I will explain Smart Flash cache feature of Oracle Exadata in this article.
Before this post, If you don’t know What is the Exadata and want to learn, you can read following Exadata Tutorials.
One of Exadata’s unique and perfect features is the Smart Flash Cache. Exadata moves frequently accessed data ( Table, Headers of Table, Index, Controlfile and Datafile ) to Flash cache and process these data in the Flash cache to avoid I/O latencies.
Smart Flash Cache feature is performed automatically in the Storage Server without the user having to take any action.
The Smart Flash Cache feature is a very smart mechanism, so it decides which data is kept in Flash cache without the intervention of users. But Exadata provides users CELL_FLASH_CACHE feature to cache some of the objects’ segments and give priority to the caching of these objects. In general, the Smart Flash Cache feature is very smart feature in that it does not cache data that is rarely or never used.
Architecture of Smart Flash cache is like following.
There are 56 PCI flash cards in a full X4-2 machine as follows and 44.8 TB raw physical flash memory. These sizes and counts may change in the Exadata X5, X6, X7 and X8.
There are 4 PCI flash memories with 3.2 TB in each Storage Server. The Smart Flash Cache settings are done the first installation and can be changed after first installation.
You can connect to each Storage Server and execute the following queries with the CellCLI tool and query the Flash Cache’s name, size, status and mode.