Beginning with Exadata Storage Server Software 18.104.22.168.0 Oracle introduce a new Feature named Flash cache compression. The goal of Flash cache compression is to dynamical and transparently compressing user data when it is loaded into the flash cache. This increase the logical capacity of the flash cache because much more data is kept in the flash and decrease the I/O on the data disk. The compression and decompression operations are completely transparent to the application and database, and Oracle says that there is no performance overhead, even when running at rates of millions of I/Os per second. Please keep in mind that there are additional licenses needed to use this feature. Please refer to licensing requirements listed in the Exadata Licensing Guide before enabling this feature.
Oracle Advanced Compression Option must be licensed to enable flash cache compression.
- Exadata uses compression to expand smart flash cache
- Data is compressed when written to flash cache
- Data is automatically decompressed when read from flash cache
Up to 2X more data fits in smart flash cache, so flash hit rates willimprove and performance will improve for large data sets
- Flash cache compression is implemented in hardware
- ZERO performance overhead
- Supported on X3 or X4 storage servers (requires F40 or F80 cards)
Flash Cache Compression is only avaible on Exadata Storage Servers X3 and later. If you try to enable it on a incompatible Storage Server you will get a error like this.
CellCLI> alter cell flashCacheCompress=TRUE CELL-02839: Flash cache compression is not supported.
As always comments are welcome