> 4. Even if we could accurately estimate the percentage of the table
> that is cached, what then?  For example, suppose that a user issues a
> query which retrieves 1% of a table, and we know that 1% of that table
> is cached.  How much of the data that the user asked for is cache?
> Hard to say, right?  It could be none of it or all of it.  The second
> scenario is easy to imagine - just suppose the query's been executed
> twice.  The first scenario isn't hard to imagine either.
I have a set of slow disks which can impact performance nearly as much as in
cached in memory versus the fast disks.

How practical would it be for analyze to keep a record of response times for
given sections of a table as it randomly accesses them and generate some
kind of a map for expected response times for the pieces of data it is

It may well discover, on it's own, that recent data (1 month old or less)
has a random read response time of N, older data (1 year old) in a different
section of the relation tends to have a response time of 1000N, and really
old data (5 year old) tends to have a response time of 3000N.

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