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Introduction
Apache Oozie is a Hadoop workflow scheduler. It is a system that manages the workflow of dependent tasks. Users can design Directed Acyclic Graphs of workflows that can be run in parallel and sequentially in Hadoop.
Image: https://oozie.apache.org/
Apache Oozie is an important topic in Data Engineering, so we shall discuss some Apache Oozie interview questions and answers. These questions and answers will help you prepare for Apache Oozie and Data Engineering Interviews.
Read more about Apache Oozie here.
Interview Questions on Apache Oozie
1. What is Oozie?
Oozie is a Hadoop workflow scheduler. Oozie allows users to design Directed Acyclic Graphs of workflows, which can then be run in Hadoop in parallel or sequentially. It can also execute regular Java classes, Pig operations, and interface with HDFS. It can run jobs both sequentially and concurrently.
2. Why do we need Apache Oozie?
Apache Oozie is an excellent tool for managing many tasks. There are several sorts of jobs that users want to schedule to run later, as well as tasks that must be executed in a specified order. Apache Oozie can make these types of executions much easier. Using Apache Oozie, the administrator or user can execute multiple independent jobs in parallel, run the jobs in a specific sequence, or control them from anywhere, making it extremely helpful.
3. What kind of application is Oozie?
Oozie is a Java Web App that runs in a Java servlet container.
4. What exactly is an application pipeline in Oozie?
It is important to connect workflow jobs that run regularly but at various times. Multiple successive executions of a process become the input to the following workflow. When these procedures are chained together, the outcome is referred to as a data application pipeline.
5. What is a Workflow in Apache Oozie?
Apache Oozie Workflow is a set of actions that include Hadoop MapReduce jobs, Pig jobs, and so on. The activities are organized in a control dependency DAG (Direct Acyclic Graph) that governs how and when they can be executed. hPDL, an XML Process Definition Language, defines Oozie workflows.
6. What are the major elements of the Apache Oozie workflow?
The Apache Oozie workflow has two main components.
- Control flow nodes: These nodes are used to define the start and finish of the workflow, as well as to govern the workflow’s execution path.
- Action nodes are used to initiate the processing or calculation task. Oozie supports Hadoop MapReduce, Pig, and File system operations and system-specific activities like HTTP, SSH, and email.
7. What are the functions of the Join and Fork nodes in Oozie?
In Oozie, the fork and join nodes are used in tandem. The fork node divides the execution path into multiple concurrent paths. The join node combines two or more concurrent execution routes into one. The join node’s descendants are the fork nodes that connect concurrently to form join nodes.
Syntax:
< fork name=”[FORK-NODE-NAME]” >
< path start=”[NODE-NAME]” / >
…
< path start=”[NODE-NAME]” / >
< /fork >
…
< join name=”[JOIN-NODE-NAME]” to=”[NODE-NAME]” / >
8. What are the various control nodes in the Oozie workflow?
The various control nodes are:
- Start
- End
- Kill
- Decision
- Fork & Join Control nodes
9. How can I set the start, finish, and error nodes for Oozie?
This can be done in the following Syntax:<error
“[A custom message]”
10. What exactly is an application pipeline in Oozie?
It is important to connect workflow jobs that run regularly but at various times. Multiple successive executions of a process become the input to the following workflow. When these procedures are chained together, the outcome is referred to as a data application pipeline.
11. What are Control Flow Nodes?
The mechanisms that specify the beginning and end of the process are known as control flow nodes (start, end, fail). Furthermore, control flow nodes give way for controlling the workflow’s execution path (decision, fork, and join)
12. What are Action Nodes?
The mechanisms initiating the execution of a computation/processing task are called action nodes. Oozie supports a variety of Hadoop actions out of the box, including Hadoop MapReduce, Hadoop file system, Pig, and others. In addition, Oozie supports system-specific jobs such as SSH, HTTP, email, and so forth.
13. Are Cycles supported by Apache Oozie Workflow?
Apache Oozie Workflow does not support cycles. Workflow definitions in Apache Oozie must be a strict DAG. If Oozie detects a cycle in the workflow specification during workflow application deployment, the deployment is aborted.
14. What is the use of the Oozie Bundle?
The Oozie bundle enables the user to run the work in batches. Oozie bundle jobs are started, halted, suspended, restarted, re-run, or killed in batches, giving you more operational control.
15. How does a pipeline work in Apache Oozie?
The pipeline in Oozie aids in integrating many jobs in a workflow that runs regularly but at different intervals. The output of numerous workflow executions becomes the input of the next planned task in the workflow, which is conducted back to back in the pipeline. The connected chain of workflows forms the Oozie pipeline of jobs.
16. Explain the role of the Coordinator in Apache Oozie?
To resolve trigger-based workflow execution, the Apache Oozie coordinator is employed. It provides a basic framework for providing triggers or predictions, after which it schedules the workflow depending on those established triggers. It enables administrators to monitor and regulate workflow execution in response to cluster conditions and application-specific constraints.
17. What is the decision node’s function in Apache Oozie?
Switch statements are decision nodes that conduct different jobs dependent on the conclusion of another expression.
18. What are the various control flow nodes offered by Apache Oozie workflows for starting and terminating the workflow?
The following control flow nodes are supported by Apache Oozie workflow and start or stop workflow execution.
- Start Control Node – The start node is the initial node to which an Oozie workflow job transfers and serves as the workflow job’s entry point. One start node is required for each Apache Oozie workflow definition.
- End Control Node – The end node is the last node to which an Oozie workflow task transfers, which signifies that the workflow job was completed. When a workflow task reaches the end node, it completes, and the job status switches to SUCCEED. One end node is required for every Apache Oozie workflow definition.
- The kill control node allows a workflow job to kill itself. When a workflow task reaches the kill node, it terminates in error, and the job status switches to KILLED.
19. What are the various control flow nodes that Apache Oozie workflows offer for controlling the workflow execution path?
The following control flow nodes are supported by Apache Oozie workflow and control the workflow’s execution path.
- Decision Control Node – A decision control node is similar to a switch-case statement because it allows a process to choose which execution path to take.
- Fork and Join Control Nodes – The fork and join control nodes work in pairs and function as follows. The fork node divides a single execution path into numerous concurrent execution paths. The join node waits until all concurrent execution paths from the relevant fork node arrive.
20. What is the default database Oozie uses to store job ids and statuses?
Oozie stores job ids and job statuses in the Derby database.
Conclusion
These Apache Oozie Interview Questions can assist you in becoming interview-ready for your upcoming personal interview. In Oozie-related interviews, interviewers usually ask the interviewee these .
To sum up:
- Apache Oozie is a distributed scheduling system to launch and manage Hadoop tasks.
- Oozie allows you to combine numerous complex jobs that execute in a specific order to complete a larger task.
- Two or more jobs within a specific set of tasks can be programmed to execute in parallel with Oozie.
The real reason for adopting Oozie is to manage various types of tasks that are being handled in the Hadoop system. The user specifies various dependencies between jobs in the form of a DAG. This information is consumed by Oozie and handled in the order specified in the workflow. This saves the user time when managing the complete workflow. Oozie also determines the frequency at which a job is executed.
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