Ecila meets Twiddledee and Twiddledum - and sends them ahead
Originally written by
- One property of disks - is that they work better sequentially, fetching
large amounts of data.
- One property of applications - is their tendency to perform sequential I/O.
- Thus, devices (and file-systems) are often configured to perform
- The "read-ahead" is sent immediately after the application read...
- ...and returns quickly after.
- Thus, when the application will want to read the next page - we'll find it
in the cache.
- If the application won't need the next pages - we wasted disk bandwidth...
- ...and possibly evicted other cached pages from memory.
- Thus, for applications that perform random reads - read-ahead is
a bad feature.