Distributed Database Systems, 1st Edition by Chhanda Ray

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Distributed Database Systems

where C is a constant that measures the ratio between the cost of an update and a retrieval

access. Typically, update accesses are more expensive and C  1. R

i

is allocated at all sites j*

where B

ij*

is positive. When B

ij*

is negative, a single copy of R

i

is placed at the site where B

ij

B

ij*

is maximum.

(iii) In this case, the benefi t of additional replica of a fragment is evaluated in terms of availability

and reliability. Let d

i

denote the degree of replicas, or R

i

and F

i

denote the benefi t of having R

i

fully replicated at each site. The benefi t function can be defi ned as

(d

i

)(12

1d

i

)F

i

Now, the benefi t of ...