This article was written before SSD’s became common in laptops.
- Flash usage
- OS/File systems will use flash as extended RAM
- No log so they need to write more quickly to persistent storage
- DBMSes will use flash as extended persistent storage
- System-wide checkpoints that flush the log and buffers
- B-Trees should use different size of I/O for flash than they currently due
with disc (due to seek time)
- The flash / disk trade-off is interesting since the brake even point for pages
is a little over 2 hours
- The author notes that original reports prediction for 20 years into the future
was “amazingly accurate” for RAM versus disk (5 hours predicted / 6 actual)
- The author also discusses the issue of energy efficiency as part of the
trade-off
- Not only in battery powered devices but also in server farms
- Future Work
- CPU should be measured in terms of cache line replacements, not instructions
- I found this interesting as a lot of experiments have shown cache misses
to be a major bottleneck in computation throughput
- In a database, short access times to data on flash allow for less
multi-programming
- I note that often we overlapped work with I/O in databases
- The author notes that less multi-programming could reduce lock contention
and could possibly allow for coarser grained locking.
- GC could also benefit from flash, some objects may live for long periods of
time but not need to be accessed frequently