Non-SQL Which of the following is/are correct? Select one or more: O a. Columns

Question

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. Answer - a,b,d because in a column oriented no sql database like cassandra columns are the basic unit. A column family is created where a column can be added dynamically as the data is inserted. A row-key is created with one or kore column whose values are used to generate a hash value, which is used to map the location for the row. So columns are used for load balancing.

2. Answer- b, d - In nosql we do not normaize the data like in rdms which result in lot of redundancy. If we are storing a particular piece of information in several documents/column families then an update or delete may create some inconsistencies if the transaction is not atomic which itself is not guranteed by any nosql databse. Yes Joins can slow the performance as delaing with large data can create a lot of garbage in memory for a single query.

3. c, e - When we are creating a replication for a particular data set, first of all it should be store on a different machine than the primary data machine. Once we have replication, queries can be redirected to both primary data machine and the replication machine for load balancing which improves the performance. Now suppose if due to some technical issue one machine goes down then other machine can serve the data independently resulting in high availability.

4. a,b,d.

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