Databases Reference
In-Depth Information
Figure 16.2 All-beneficial sites method for data allocation, showing remote query and update for
transaction T1 originating at site S1.
To t a l - c o s t
2
< Total-cost
1
.
Expanding terms and simplifying, we get in succession:
Q1(local) + U1(local) + U1(remote) + Q2(local) + U2(local)
+ U2(remote) < Q1(local) + U1(local) + Q2(remote) + U2(remote)
U1(remote) + Q2(local) + U2(local) < Q2(remote).
Q2(remote) - Q2(local) > U1(remote) + U2(local),
which is the relationship that defines the all-beneficial sites method, in other words, the
benefit is the difference between a remote and local query time to tab1, and the cost is
the sum of the local and remote update times for the new copy of tab1.
