data base non-sql Which of the following is/are correct? Select one or more: O a
ID: 3601899 • Letter: D
Question
data base non-sql
Which of the following is/are correct? Select one or more: O a. Columns are grouped into column families, and columns within a column family can be dynamically changed O b. Columns are the basic units of distribution and load balancing c. Tablets are the basic units of access control. O d. The choice of row-keys affects partitioning of rows into tablets. O e. Column families within a (big) table can be dynamically created (i.e., no need to predefine a column family before data is stored under any column key in that family). Which of the following about JOIN operations is/are correct? Select one or more: O a. The JOIN operations are essential for developing efficient autosharding technologies. O b. The lack of JOIN operations in a NoSQL database could lead to data redundancy and data inconsistency c. The JOIN operations have been added in the first generation for NoSQL but deprecated. d. The JOIN operations are not common in NoSQL databases because they could make the query processing sloW.Explanation / Answer
1.
Option a is correct, as column families are nothing but tuples having column groups saved in form of key and value pair.
Option b is incorrect because in no sql databases, tablet a.k.a row range is the basic unit of distribution and loadbalancing
Option c is incorrect because column familoes arr basic unit of access control
Option d correct because a target comprises of row range which is defined using row keys
Option e is correct column family should be created before adding data in any column key in that family
#2 c and d are correct as per the description with the points
#3 Data Replication is the process of storing data in more than one site or node
Option c is correct because, sites containing relation R can process queries (involving relation R) in parallel
Option e is correct, If one of the sites containing relation R fails, then the relation R can be obtained from another site.
#4
Option a is incorrect, sorting is not a mandate, map workers invoke a map function which can be anything
Option b is incorrect, because a failed map task is allocated to the same computing node right after its failure. this allows to restart it from local checkpoints produced so far
Option c is correct
Option d is correct
Option e is incorrect because master is responsible for forwarding files to the reduce workers.
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