:I really dislike the idea of random expiration; I don't understand
:the point, unless you are trying to get better numbers on some
:..
Well, the basic scenario is something like this: Lets say you have
512MB of ram and you are reading a 1GB file sequentially, over and over
again. The cache scenario that gives you the greatest performance is
basically to keep 512MB worth of the file in memory and throw away the
rest as you read it.
This is effectively what random disk cache expiration gives you (assuming
you expire whole tracks worth of data, not just random pages). i.e. it's
only useful when you are cycling through a data set that is larger then
main memory over and over again.
Most people deal with this issue simply by beefing up their disk
subsystem. After all, you don't have to stripe very many disks (only
2 or 3) to get 100MB/sec+ in throughput from the disk subsystem.
-Matt
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