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node has no requests, we
AND
together the trees generated for each of
P
's
execution subplans, since these are orthogonal (case 2). Otherwise, if the root
of
P
has a request, the answer depends on the type of node. If it is a join, its
request
ρ
corresponds to an attempted index-based join alternative. We know
that
ρ
and the requests on
P
's right subplan are mutually exclusive (see
ρ
3
and
ρ
3
=500×(T
3
,E={(z,1)},R=ø
P=ø, O=ø, A={b,z})
T
1
.w=T
2
.y
T
1
.w=T
3
.z
ρ
4
=2500×(T
3
,E={(z,0.2)},...
R=ø, P=ø, O=ø, A={b,z})
ρ
2
=2500×(T
2
,E={(y,0,2)},
R=ø, P=ø, O=ø, A={y})
ρ
1
=1×(T
1
,E={(a,2500)},
R=ø, P=ø, O=ø,
A={a,x,w})
T
1
.w=T
3
.z
T
1
.x=T
2
.y
ρ
5
=1×(T
3
,E={(b,2500)},
R=ø, P=ø, O=ø,
A={b,z})
σ
T
1
.a=5
σ
T
3
.b=8
T
1
T
2
T
3
(a) Fragment of the search space.
Hash Join
[T1.w=T3.z]
ρ
3
ρ
2
Hash Join
[T1.x=T2.y]
ρ
1
ρ
5
Filter
[T1.a=5]
Filter
[T3.b=8]
Scan
[T1]
Scan
[T2]
Scan
[T3]
(b) Final execution plan.
FIGURE 10.2
Gathering information during optimization. (Used with per-
mission from Bruno, N. & Chaudhuri, S. In
Proceedings of the International
Conference on Very Large Databases [VLDB],
2006.)
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