Oracle Database Interview Questions & Answers Set-20

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1. In which language MongoDB is written?
Ans: MongoDB is written and implemented in C++.


2. Does MongoDB need a lot space of Random Access Memory (RAM)?
Ans: No. MongoDB can be run on small free space of RAM.


3. What language you can use with MongoDB?
Ans: MongoDB client drivers supports all the popular programming languages so there is no issue of language, you can use any language that you want.


4. Does MongoDB database have tables for storing records?
Ans: No. Instead of tables, MongoDB uses "Collections" to store data.


5. Do the MongoDB databases have schema?
Ans: Yes. MongoDB databases have dynamic schema. There is no need to define the structure to create collections.


6. What is the method to configure the cache size in MongoDB?
Ans: MongoDB's cache is not configurable. Actually MongoDb uses all the free spaces on the system automatically by way of memory mapped files.


7. How to do Transaction/locking in MongoDB?
Ans: MongoDB doesn't use traditional locking or complex transaction with Rollback. MongoDB is designed to be light weighted, fast and predictable to its performance. It keeps transaction support simple to enhance performance.


8. Why 32 bit version of MongoDB are not preferred ?
Ans: Because MongoDB uses memory mapped files so when you run a 32-bit build of MongoDB, the total storage size of server is 2 GB. But when you run a 64-bit build of MongoDB, this provides virtually unlimited storage size. So 64-bit is preferred over 32-bit.


9. Is it possible to remove old files in the moveChunk directory?
Ans: Yes, These files can be deleted once the operations are done because these files are made as backups during normal shard balancing operation. This is a manual cleanup process and necessary to free up space.


10. What will have to do if a shard is down or slow and you do a query?
Ans: If a shard is down and you even do query then your query will be returned with an error unless you set a partial query option. But if a shard is slow them Mongos will wait for them till response.


11. What is Cassandra?
Ans: Cassandra is a one of the NoSQL distributed database system. It is an open source data storage system effectively designed to store and manages large volume of data without any failure.


12. In which language Cassandra is written?
Ans: Cassandra is written in Java. It is originally designed by Facebook consisting of flexible schemas. It is highly scalable for big data.


13. What are the benefits/ advantages of Cassandra?
Ans: Advantages/ Benefits of Cassandra:
  • Cassandra was designed to handle big data workloads across multiple nodes without any single point of failure.
  • Cassandra delivers near real-time performance simplifying the work of Developers, Administrators, Data Analysts and Software Engineers.
  • It provides extensible scalability and can be easily scaled up and scaled down as per the requirements.
  • It is fault tolerant and consistent.
  • It is a column-oriented database.
  • It has no single point of failure.
  • There is no need for separate caching layer.
  • It has flexible schema design.
  • It has flexible data storage, easy data distribution, and fast writes.
  • It supports ACID (Atomicity, Consistency, Isolation, and Durability) properties.
  • It has multi-data center and cloud capable.

14. How Cassandra stores data?
Ans: Cassandra stores all data as bytes. When you specify validator, Cassandra ensures that those bytes are encoded as per requirement and then a comparator orders the column based on the ordering specific to the encoding.


15. What are the main components of Cassandra data models?
Ans: Following are the main components of Cassandra data model:
  • Cluster
  • Keyspace
  • Column
  • Column & Family
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