About Joe Stein

Apache Solr real-time live index updates at scale with Apache Hadoop

Episode # 22 of the podcast was a talk with Patrick Hunt

We talked about the new work that has gone into Apache Solr (upstream) that allows it to work on Apache Hadoop. Solr has support for writing and reading its index and transaction log files to the HDFS distributed filesystem. This does not use Hadoop Map-Reduce to process Solr data, rather it only uses the HDFS filesystem for index and transaction log file storage. https://cwiki.apache.org/confluence/display/solr/Running+Solr+on+HDFS

We also talked about Solr Cloud and how the sharding features allow Solr to scale with a Hadoop cluster https://cwiki.apache.org/confluence/display/solr/SolrCloud.

Apache Solr includes the ability to set up a cluster of Solr servers that combines fault tolerance and high availability. Called SolrCloud, these capabilities provide distributed indexing and search capabilities, supporting the following features:

  • Central configuration for the entire cluster
  • Automatic load balancing and fail-over for queries
  • ZooKeeper integration for cluster coordination and configuration.

SolrCloud is flexible distributed search and indexing, without a master node to allocate nodes, shards and replicas. Instead, Solr uses ZooKeeper to manage these locations, depending on configuration files and schemas. Documents can be sent to any server and ZooKeeper will figure it out.

Patrick introduced me to Morphlines (part of the Cloudera Development Kit for Hadoop) http://cloudera.github.io/cdk/docs/current/cdk-morphlines/index.html

Cloudera Morphlines is an open source framework that reduces the time and skills necessary to build and change Hadoop ETL stream processing applications that extract, transform and load data into Apache Solr, HBase, HDFS, Enterprise Data Warehouses, or Analytic Online Dashboards. Want to build or facilitate ETL jobs without programming and without substantial MapReduce skills? Get the job done with a minimum amount of fuss and support costs? Here is how to get started.

A morphline is a rich configuration file that makes it easy to define a transformation chain that consumes any kind of data from any kind of data source, processes the data and loads the results into a Hadoop component. It replaces Java programming with simple configuration steps, and correspondingly reduces the cost and integration effort associated with developing and maintaining custom ETL projects.

Morphlines is a library, embeddable in any Java codebase. A morphline is an in-memory container of transformation commands. Commands are plugins to a morphline that perform tasks such as loading, parsing, transforming, or otherwise processing a single record. A record is an in-memory data structure of name-value pairs with optional blob attachments or POJO attachments. The framework is extensible and integrates existing functionality and third party systems in a straightforward manner.

The morphline commands were developed as part of Cloudera Search. Morphlines power ETL data flows from Flume and MapReduce and HBase into Apache Solr. Flume covers the real time case, whereas MapReduce covers the batch processing case. Since the launch of Cloudera Search morphline development graduated into the Cloudera Development Kit(CDK) in order to make the technology accessible to a wider range of users and products, beyond Search. The CDK is a set of libraries, tools, examples, and documentation focused on making it easier to build systems on top of the Hadoop ecosystem. The CDK is hosted on GitHub and encourages involvement by the community. For example, morphlines could be embedded into Crunch, HBase, Impala, Pig, Hive, or Sqoop. Let us know where you want to take it!

Morphlines can be seen as an evolution of Unix pipelines where the data model is generalized to work with streams of generic records, including arbitrary binary payloads. A morphline is an efficient way to consume records (e.g. Flume events, HDFS files, RDBMS tables or Avro objects), turn them into a stream of records, and pipe the stream of records through a set of easily configurable transformations on the way to a target application such as Solr, for example as outlined in the following figure:

morphlines

In this figure, a Flume Source receives syslog events and sends them to a Flume Morphline Sink, which converts each Flume event to a record and pipes it into a readLine command. The readLine command extracts the log line and pipes it into a grok command. The grok command uses regular expression pattern matching to extract some substrings of the line. It pipes the resulting structured record into the loadSolr command. Finally, the loadSolr command loads the record into Solr, typically a SolrCloud. In the process, raw data or semi-structured data is transformed into structured data according to application modelling requirements.

The Morphline framework ships with a set of frequently used high level transformation and I/O commands that can be combined in application specific ways. The plugin system allows the adding of new transformations and I/O commands and integrates existing functionality and third party systems in a straightforward manner.

This integration enables rapid Hadoop ETL application prototyping, complex stream and event processing in real time, flexible log file analysis, integration of multiple heterogeneous input schemas and file formats, as well as reuse of ETL logic building blocks across Hadoop ETL applications.

The CDK ships an efficient runtime that compiles a morphline on the fly. The runtime executes all commands of a given morphline in the same thread. Piping a record from one command to another implies just a cheap Java method call. In particular, there are no queues, no handoffs among threads, no context switches and no serialization between commands, which minimizes performance overheads.

Morphlines manipulate continuous or arbitrarily large streams of records. A command transforms a record into zero or more records. The data model can be described as follows: A record is a set of named fields where each field has an ordered list of one or more values. A value can be any Java Object. That is, a record is essentially a hash table where each hash table entry contains a String key and a list of Java Objects as values. Note that a field can have multiple values and any two records need not use common field names. This flexible data model corresponds exactly to the characteristics of the Solr/Lucene data model.

Not only structured data, but also binary data can be passed into and processed by a morphline. By convention, a record can contain an optional field named _attachment_body, which can be a Java java.io.InputStream or Java byte[]. Optionally, such binary input data can be characterized in more detail by setting the fields named _attachment_mimetype (such as “application/pdf”) and _attachment_charset (such as “UTF-8″) and _attachment_name (such as “cars.pdf”), which assists in detecting and parsing the data type. This is similar to the way email works.

This generic data model is useful to support a wide range of applications. For example, the Apache Flume Morphline Solr Sink embeds the morphline library and executes a morphline to convert flume events into morphline records and load them into Solr. This sink fills the body of the Flume event into the _attachment_body field of the morphline record, as well as copies the headers of the Flume event into record fields of the same name. As another example, the Mappers of the MapReduceIndexerTool fill the Java java.io.InputStream referring to the currently processed HDFS file into the _attachment_body field of the morphline record. The Mappers of the MapReduceIndexerTool also fill metadata about the HDFS file into record fields, such as the file’s name, path, size, last modified time, etc. This way a morphline can act on all data received from Flume and HDFS. As yet another example, the Morphline Lily HBase Indexer fills a HBase Result Java POJO into the _attachment_body field of the morphline record. This way morphline commands such as extractHBaseCells can extract data from HBase updates and correspondingly update a Solr index.

We also talked a good deal about Apache Zookeeper and some of the history back from when Zookeeper was originally at Yahoo! and Patrick’s experience since then. To hear everything that Patrick had to say please subscribe to the podcast.

 

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