Oracle flash drive recommendations

Oracle flash drive recommendations

EFD-friendly DB workloads

Not as cost-effective on EFD

Random reads B-Tree leaf access ROWID look up into Table Access to out-of-line LOB Access to overflowed row Index scan over Unclustered Table Compression: Increases I/O intensity (IOPS/GB) Serial reads Random writes Row update by PK Index maintenance Reduce checkpoint interval TEMP: Sort areas and Intermediate tables Sequentially read and written but I/O done in 1 MB units: not enough to amortize seeks Lower Latency: Get In, Get Out

Redo log files Sequentially read and written and commit latency already handled by cache in storage controller Undo table space Sequentially written, randomly read by flashBack. But reads are for recently written data that is likely to still be in the buffer cache Large table scans Buffer pools with lots of writes Mismatch between read and write latency characteristics of EFDs can cause unwanted “Free Buffer Waits”. Buffer pool tuning is necessary after deploying EFDs

Reference from Oracle Openworld 2008 presentation

Redo Logs on EFDs? (or not)

It is a common misconception that Oracle online redo logs will benefit by moving them on EFDs, whereas all the experimental data indicates the opposite position. Testing has shown that moving redo logs on to EFDs results in a low percentage of improvement. It is better to leave them on the write cache backed Fibre Channel drives rather than moving them on to EFDs, thereby using EFDs for other read intensive parts of the database like indexes or data.

Oracle TEMP tablespace on EFDs

Oracle uses this space mainly for data aggregations and sorting. When the database engine cannot fit the sorts in memory, they will be spilled on to disk for storing intermediary results. Oracle typically does large sequential I/Os against these tablespaces in the context of single user. When multiple users are performing concurrent sorts on these tablespaces, the I/O turns out to be largely random in nature.  Even though EFDs do not provide as much benefit for large random I/O as they provide to small random operations, still they are far ahead of what regular rotation Fibre Channel drives can deliver. Depending on the availability of space on EFDs, Oracle applications will be benefited by moving the temporary tablespaces to them. Temporary tablespace files should only be moved to EFDs after all the I/O intensive parts have been moved to them.