Two mark questions with answers in Distributed database / Important two mark questions and answers in distributed database
Two mark questions (To know more, please click the links)
- List the fragmentation types.
Vertical fragmentation
Hybrid fragmentation
- Give the different strategies used for placement of data in distributed database.
What are the advantages of allocation
of fragments?
Locality of reference – data are close
where they are required
Improved reliability and availability
– data are highly available
Balanced storage and cost – simple
hard disks are fine. Cost effective.
Minimal communication cost -
Communication cost is less
Completeness
Reconstruction
Dis-jointness
Loss of message
Communication link failure
Site failure.
Who is transaction coordinator?
In distributed database, the site in
which a transaction is initiated is completely responsible for finishing the
transaction. This is done by the Transaction Manager of that particular site.
That site’s Transaction Manager is called as transaction coordinator.
Define replication
Creating a copy of existing data or
table is called replication. It increases availability at the cost of
redundancy.
List down some advantages of DDBMSs.
Reflects organizational structure
Improved ability to share and local
autonomy
Improved availability
Improved reliability
Improved performance
Economy in deploying software and
hardware resources
Modular growth of the system
Integration
Name some disadvantages of fragmentation.
Performance degradation in case of
larger applications which handles required data from several sites.
Integrity control may be more
difficult as the data are stored at multiple sites.
What is Primary Horizontal fragmentation?
Primary Horizontal fragmentation is a
fragmentation technique which fragments (partitions) a single relation (table) using
a set of min-term fragments.
List down the steps involved in Primary horizontal fragmentation.
Identify set of simple predicates.
Construct set of min-term predicates
using simple predicates.
Eliminate redundant or unnecessary min-term
predicates.
Use all valid min-term predicates to create
fragments.
What is Derived horizontal fragmentation?
It is a horizontal fragmentation
process where a table is fragmented based on the fragments that are created by horizontal
fragmentation process of another table (parent table – think about primary key
foreign key relationship).
Define fragmentation transparency.
The end users of a distributed
database system need not know about how the database is fragmented. Hiding the information
about how a table is fragmented from
the end user is called fragmentation
transparency.
Who is the transaction coordinator in distributed transactions?
The module of a distributed site which
coordinates the transactions that are initiated at that site is called
transaction coordinator. Let us assume that you have configured a distributed
database system where we have sites A, B, C, and D containing different or same
data. Any transaction requested at one of the sites say A, and in need of data available
at sites B, and C, the transaction coordinator of site A is responsible to process
the requested data at other sites.
What are the roles of transaction manager?
Maintaining a log for recovery
purposes
Coordinating the concurrent
transactions that are executed at that site.
List down the roles of transaction coordinator.
Starting the execution of a
transaction initiated at that site.
Breaking the transaction into a set of
sub-transactions if needed.
Distributing the sub-transactions to different
sites.
Coordinating the completion of the
transaction.
What are the messages used by 2 Phase Commit protocol?
<prepare T>
<no T>
<ready T>
<abort T>
<commit T>
What are the two phases of 2PC protocol?
Phase 1: Obtaining the decision –
whether to commit or abort a transaction T.
Phase 2: Recording the decision –
implement the decision taken in phase 1.
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