Hi Norm,

Talking about optimizing using histograms - for example, an index on gender
is valuable when looking for female professional rugby players, and much
less so for males. I guess you could replace "professional rugby players"
with "open source developers", but ...

>
> > And if it happens during a nested loop join? Re-optimize on every
> record?
> I'd expect a nested loop join to already have the rows it needs in the
> driving table by the time it hits the nested loop?
>
>

Well, at least Firebird, InterBase, and MySQL (and NuoDB) execute nested
loop joins by retrieving a row from the outer loop, using its values to
look up the next inner loop and so on until all the joins are done, then
sends the result to the client. If the result has to be sorted, it gets
fed into the sorter right then. Maybe other systems get all the outer
rows, then all the next inner ... but that would lead to a lot of latency
to get the first row in all cases.

Good luck,

Ann


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