Distributed Databases
A transaction manager is which of the following?

Maintains appropriate concurrency control
Maintains before and after database images
Maintains a log of transactions
All of these

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Distributed Databases
Replication should be used when which of the following exist?

All of these
When using many nodes with different operating systems and DBMSs and database designs.
When transmission speeds and capacity in a network prohibit frequent refreshing of large tables.
The application's data can be somewhat out-of-date.

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Distributed Databases
Which of the following is a disadvantage of replication?

Reduced network traffic
If the database fails at one site, a copy can be located at another site.
Each site must have the same storage capacity.
Each transaction may proceed without coordination across the network.

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