# Database: Distributed Databases

Name: _________________________________

CLOSED BOOK. Each possible answer is worth one point.

1. A replicated database
   1. Is duplicated on one or more other systems.
   2. Allocates some tables only to one system and others only to another system.
2. Which are true of a replicated database? Mark all correct answers.
   1. Performance can be improved because the load can be distributed over several systems.
   2. Performance may be decreased because updates have to propagate to all copies.
   3. Reliability is generally decreased because because there are more systems that can fail.
   4. Scalability is generally more expensive because entirely new systems have to be purchased to increase the capacity.
   5. DB administration is more complex.
   6. Vendor lock-in is prevented because different replicated copies can run different DBMSs and communicate with standard Internet protocols.
3. What does transparency mean?
   1. The DBA doesn't have to know where parts of the database are.
   2. The DB appears as a single database to a user, regardless of where the parts are allocated.
   3. Tables that are allocated remotely are transparent, ie can't be seen by the user.
   4. Performance is always approximately the same because load balancing adjusts for varying demands on the systems.
4. Which is NOT a kind of fragmentation?
   1. Horizontal fragmentation.
   2. Vertical fragmentation.
   3. Diagonal fragmentation.
   4. Mixed fragmentation.
5. When searching a fragmented table, the user
   1. Must compose individual SQL commands for each part of the table, and merge the results, eg with the `UNION` command.
   2. Can write a command as tho the table was not fragmented and let the SQL query processor figure out how to make the query work on the separate fragments.