This chapter includes the following sections:
Typical processing in Hadoop includes data validation and transformations that are programmed as MapReduce jobs. Designing and implementing a MapReduce job requires expert programming knowledge. However, when you use Oracle Data Integrator, you do not need to write MapReduce jobs. Oracle Data Integrator uses Apache Hive and the Hive Query Language (HiveQL), a SQL-like language for implementing MapReduce jobs.
When you implement a big data processing scenario, the first step is to load the data into Hadoop. The data source is typically in Files or SQL databases.
After the data is loaded, you can validate and transform it by using HiveQL like you use SQL. You can perform data validation (such as checking for NULLS and primary keys), and transformations (such as filtering, aggregations, set operations, and derived tables). You can also include customized procedural snippets (scripts) for processing the data.
When the data has been aggregated, condensed, or processed into a smaller data set, you can load it into an Oracle database, other relational database, HDFS, HBase, or Hive for further processing and analysis. Oracle Loader for Hadoop is recommended for optimal loading into an Oracle database.
For more information, see Chapter 4, "Integrating Hadoop Data".
By default, Oracle Data Integrator (ODI) uses HiveQL to implement the mappings. However, Oracle Data Integrator also lets you to implement the mappings using Pig Latin and Spark Python. Once your mapping is designed, you can either implement it using the default HiveQL, or choose to implement it using Pig Latin or Spark Python.
Support for Pig Latin and Spark Python in ODI is achieved through a set of component KMs that are specific to these languages. These component KMs are used only when a Pig data server or a Spark data server is used as the staging location for your mapping.
For example, if you use a Pig data server as the staging location, the Pig related KMs are used to implement the mapping and Pig Latin code is generated. Similarly, to generate Spark Python code, you must use a Spark data server as the staging location for your mapping.
For more information about generating code in different languages and the Pig and Spark component KMs, see the following:
Apache Oozie is a workflow scheduler system that helps you orchestrate actions in Hadoop. It is a server-based Workflow Engine specialized in running workflow jobs with actions that run Hadoop MapReduce jobs. Implementing and running Oozie workflow requires in-depth knowledge of Oozie.
However, Oracle Data Integrator does not require you to be an Oozie expert. With Oracle Data Integrator you can easily define and execute Oozie workflows.
Oracle Data Integrator allows you to automatically generate an Oozie workflow definition by executing an integration project (package, procedure, mapping, or scenario) on an Oozie engine. The generated Oozie workflow definition is deployed and executed into an Oozie workflow system. You can also choose to only deploy the Oozie workflow to validate its content or execute it at a later time.
Information from the Oozie logs is captured and stored in the ODI repository along with links to the Oozie UIs. This information is available for viewing within ODI Operator and Console.
For more information, see Chapter 5, "Executing Oozie Workflows".
ODI provides the following two modes for executing the Oozie workflows:
Task mode generates an Oozie action for every ODI task. This is the default mode.
The task mode cannot handle the following:
KMs with scripting code that spans across multiple tasks.
KMs with transactions.
KMs with file system access that cannot span file access across tasks.
ODI packages with looping constructs.
Session mode generates an Oozie action for the entire session.
ODI automatically uses this mode if any of the following conditions is true:
Any task opens a transactional connection.
Any task has scripting.
A package contains loops.
Note that loops in a package are not supported by Oozie engines and may not function properly in terms of execution and/or session log content retrieval, even when running in SESSION mode.
Note:This mode is recommended for most of the use cases.
By default, the Oozie Runtime Engines use the Task mode, that is, the default value of the
OOZIE_WF_GEN_MAX_DETAIL property for the Oozie Runtime Engines is TASK.
You can configure an Oozie Runtime Engine to use Session mode, irrespective of whether the conditions mentioned above are satisfied or not. To force an Oozie Runtime Engine to generate session level Oozie workflows, set the
OOZIE_WF_GEN_MAX_DETAIL property for the Oozie Runtime Engine to SESSION.
For more information, see Section 5.2.2, "Oozie Runtime Engine Properties".