1. What is Apache ZooKeeper primarily used for in Hadoop?
Answer:
Explanation:
Apache ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services, all of which are used in coordinating and managing distributed systems.
2. ZooKeeper follows which type of architecture?
Answer:
Explanation:
ZooKeeper follows a client-server architecture where clients are the nodes (servers) in the distributed system which interact with the ZooKeeper ensemble for various coordination tasks.
3. What are Znodes in ZooKeeper?
Answer:
Explanation:
In ZooKeeper, Znodes are the data nodes that exist in its hierarchical namespace, similar to files and directories, and store configuration information and other data for distributed applications.
4. What is the role of the ZooKeeper ensemble?
Answer:
Explanation:
A ZooKeeper ensemble refers to a group of ZooKeeper servers working together to provide a highly reliable and redundant distributed coordination service.
5. How does ZooKeeper handle leader election?
Answer:
Explanation:
ZooKeeper uses a consensus protocol (such as Zab or Raft) for leader election among the servers in an ensemble to decide which server will act as the leader.
6. What is the purpose of the ZooKeeper 'watch' mechanism?
Answer:
Explanation:
The 'watch' mechanism in ZooKeeper allows clients to receive notifications about changes in the state of Znodes, such as data changes or changes in their children.
7. ZooKeeper provides which type of data consistency?
Answer:
Explanation:
ZooKeeper guarantees strong consistency, ensuring that once a write operation is completed, all subsequent reads will see that data.
8. What kind of data model does ZooKeeper use?
Answer:
Explanation:
ZooKeeper uses a hierarchical data model where data is organized in a tree-like structure, similar to a file system, with Znodes acting like files and directories.
9. How are ZooKeeper servers in an ensemble connected?
Answer:
Explanation:
ZooKeeper servers in an ensemble are connected through peer-to-peer connections, enabling them to communicate with each other to maintain the state of the system.
10. What is a session in the context of ZooKeeper?
Answer:
Explanation:
In ZooKeeper, a session represents a client's connection to a ZooKeeper server, which includes a session ID and a session timeout.
11. What happens when the leader ZooKeeper server fails?
Answer:
Explanation:
If the leader ZooKeeper server fails, a new leader is automatically elected from the remaining servers in the ensemble to ensure continued operation of the service.
12. What type of storage is used by ZooKeeper?
Answer:
Explanation:
ZooKeeper uses a combination of in-memory and on-disk storage to manage its data. In-memory storage allows for quick access, while on-disk storage provides durability.
13. What is a quorum in the context of a ZooKeeper ensemble?
Answer:
Explanation:
In a ZooKeeper ensemble, a quorum is the majority of servers that need to agree on state changes. This ensures that the system can tolerate a certain number of server failures.
14. ZooKeeper can be used for which of the following?
Answer:
Explanation:
ZooKeeper is commonly used for configuration management in distributed systems, maintaining and distributing configuration data across the system.
15. What is the maximum size of a Znode's data in ZooKeeper?
Answer:
Explanation:
The maximum size of a Znode's data in ZooKeeper is typically 1 MB. This limit is to ensure that the system remains efficient and responsive.
16. Can ZooKeeper be used for load balancing?
Answer:
Explanation:
ZooKeeper is not designed for load balancing. It is a coordination and configuration management tool, not a load balancer.
17. What happens when a ZooKeeper client loses connection to its server?
Answer:
Explanation:
If a ZooKeeper client loses connection to its server, it attempts to connect to another server in the ensemble to maintain its session and continue operations.
18. What is the ZooKeeper Atomic Broadcast (Zab) protocol used for?
Answer:
Explanation:
The Zab protocol in ZooKeeper is used for ensuring consistent data replication across all servers in the ensemble, particularly for leader election and the replication of state changes.
19. How does ZooKeeper handle concurrent writes?
Answer:
Explanation:
ZooKeeper handles concurrent writes by processing them in the order they are received, ensuring consistency and avoiding conflicts.
20. What mechanism does ZooKeeper provide for service discovery?
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Explanation:
ZooKeeper provides a centralized service registry mechanism for service discovery, where services can register themselves and clients can look them up as needed.
21. In ZooKeeper, what is ephemeral Znode?
Answer:
Explanation:
Ephemeral Znodes in ZooKeeper are temporary and exist only as long as the session that created them is active. They are automatically deleted when the session ends.
22. What is the typical use case for ZooKeeper's sequential Znodes?
Answer:
Explanation:
Sequential Znodes in ZooKeeper are used to create unique identifiers. When a sequential Znode is created, ZooKeeper automatically appends a monotonically increasing counter to its name.
23. Can ZooKeeper be used for transaction management in distributed systems?
Answer:
Explanation:
While ZooKeeper provides coordination services, it is not designed for complex transaction management in distributed systems. It is more focused on configuration, synchronization, and naming services.
24. How does ZooKeeper ensure data consistency during network partitions?
Answer:
Explanation:
ZooKeeper ensures data consistency during network partitions by using a majority-based quorum system. As long as a majority of nodes can communicate with each other, they can continue to operate and maintain consistency.
25. What is the main advantage of using ZooKeeper in a distributed system?
Answer:
Explanation:
The main advantage of using ZooKeeper in a distributed system is that it provides a reliable and efficient coordination and synchronization mechanism, which is crucial for the management and orchestration of distributed applications and services.