Block Nested Loop Join (cont)
Why block nested loop join is actually useful in practice ...
Many queries have the form
select * from R,S where r.i=s.j and r.x=K
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This would typically be evaluated as
Tmp = Sel[x=K](R)
Res = Join[i=j](Tmp, S)
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If Tmp is small ⇒ may fit in memory
(in small #buffers)
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