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· 5 min read
Jeffrey Aven

Apache Beam is an open-source project which provides a unified programming model for Batch and Streaming data pipelines.

B(atch) + str(EAM) => BEAM

Beam SDK and Execution Framework

Beam SDKs allow you to define Pipelines (in languages such as Java or Python). A pipeline is essentially a graph (a DAG - Directed Acyclic Graph) of nodes that represent transformation steps.

Apache Beam Pipeline

Pipelines can then be executed on a backend service (such as your local machine, Apache Spark, or Google Cloud Dataflow) using Runners. For instance, to run a pipeline locally, you would use the DirectRunner; to run a pipeline on Google Cloud Dataflow you would use the DataflowRunner runner.

Beam Programming Model

The PCollection is the most atomic data unit in the Beam programming model, akin to the RDD in the Apache Spark core API; it is a representation of an immutable collection of items that is physically broken down into bundles (subsets of elements for parallelization).

PCollections can be bounded (which is a batch processing pattern) or unbounded (which is a stream processing pattern).

A PTransform is an operator that takes a PCollection as an input and outputs a new PCollection with transforms applied. This is the same coarse-grained transformation pattern employed by Spark.

Beam DSL

The Beam DSL is a set of higher-order functions that can be used to construct pipelines. These functions are used to construct the graph of nodes that represent the pipeline.

Map, FlatMap and Filter

The basic Map, FlatMap and Filter functions in the Beam API work similarly to their namesakes in the Spark Core API. The Map and FlatMap functions are higher-order functions (that is, functions that have arguments of other functions) that operate on each element in a collection, emitting an output element for each input element. The Filter function can be used to only emit elements from an input PCollection that satisfy a given expression.

ParDo and DoFn

ParDo is a wrapper function for parallel execution of a user-defined function called a DoFn ("do function"), ParDo's and DoFn's are used when the basic Map and FlatMap operators are not enough. DoFns are executed in parallel on a PCollection and can be used for computational transformations or transformations other than 1:1 between inputs and outputs.

Think of these as user-defined functions to operate on a PCollection in parallel.

GroupByKey, CombineByKey

GroupByKey and CombineByKey are operators that group data (key-value pairs) by the key for each element. This is typically a precursor to some aggregate operation (such as a count or sum operation).

CoGroupByKey and Flatten

CoGroupByKey is akin to a JOIN operation in SQL (by the key for each element in two PCollections). Flatten is akin to a UNION in SQL.

Side Inputs

Side Inputs can be used with ParDo and DoFn to provide additional data, which can be used to enrich your output PCollection, or utilized within the logic of your DoFn.

Sources, Sinks and Connectors

Sources represent where data is read into an Apache Beam pipeline; sinks represent destinations where data is written out from pipelines. A Beam pipeline will contain one or more sources and sinks.

Sources can be bounded (for batch processing) or unbounded for stream processing.

Connectors can be source connectors or sink connectors to read from or write to the various sources and targets used in a Beam pipeline. Examples include FileIO and TextIO for working with files or text data, BigQueryIO for reading or writing into BigQuery, PubSubIO for reading and writing messages into Google PubSub, and much more.

Streaming and Unbounded PCollections

Streaming data sources are represented by Unbounded PCollections. Unbounded PCollections support windowing operations using Fixed Windows, Sliding Windows, or Session Windows. Watermarks are used to allow for late-arriving data to be processed within its associated time window, and Triggers can be used to control the processing of windowed batches of data.

Templates

Beam templates enable the reusability of pipelines, converting compile-time pipeline parameters to run-time arguments. Jobs (invocations of pipelines) can be launched from templates.

Templates include classic templates, where the graph for the pipeline is built (compile-time) with the template, flex templates where the pipeline graph is created when the template is launched (runtime).

In addition, Google provides several templates with Cloud Dataflow (Google-provided templates), allowing you to launch routine jobs without writing any code.

Google-provided templates are available for batch, streaming, and utility pipelines, for example:

  • Kafka to BigQuery
  • Pub/Sub Topic to BigQuery
  • Text Files on Cloud Storage to BigQuery
  • Text Files on Cloud Storage to Cloud Spanner
  • Bulk Compress or Decompress Files on Cloud Storage
  • and more

5 minutes is up! I hope you enjoyed this quick introduction to Apache Beam. If you want to learn more, check out the Apache Beam documentation.

· 4 min read
Jeffrey Aven

Kappa Architecture and Data Warehousing re-imagined

Streaming Data Warehouse

The aspiration to extend data analysis (predictive, descriptive or otherwise) to streaming event data has been common across every enterprise scale program I have been involved with. Often, however, this aspiration goes unrealised as it tends to slide down the priority scale as we still grapple with legacy batch oriented integration patterns and processes.

Event processing is not a new concept, real time event and transaction processing has been a standard feature for security, digital and operations functions for some time, however in the Data Warehousing, BI and Advanced Analytics worlds it is often spoken about but rarely implemented, except for tech companies of course. In many cases personalization is still a batch oriented process, e.g. train a model from a feature set built from historical data, generate recommendations in batch, serve these recommendations upon the next visit - wash, rinse, and repeat.

Lambda has existed for several years now as a data-processing architecture pattern designed to incorporate both batch and stream-processing capabilities. Moreover, messaging platforms have existed for decades, from point-to-point messaging systems, to message-oriented-middleware systems, to distributed pub-sub messaging systems such as Apache Kafka.

Additionally, open source streaming data processing frameworks and tools have proliferated in recent years with projects such as Storm, Samza, Flink and Spark Streaming becoming established solutions.

Kafka in particular, with its focus on durability, resiliency, availability and consistency, has graduated into fully fledged data platform not simply a transient messaging system. In many cases Kafka is serving as a back end for operational processes, such as applications implementing the CQRS (Command Query Responsibility Segregation) design pattern.

In other words, it is not the technology that holds us back, it's our lack of imagination.

Enter Kappa Architecture where we no longer have to attempt to integrate streaming data with batch processes…everything is a stream. The ultimate embodiment of Kappa Architecture is the Streaming Data Warehouse.

In the Streaming Data Warehouse, tables are represented by topics. Topics represent either:

  • unbounded event or change streams; or
  • stateful representations of data (such as master, reference or summary data sets).

This approach makes possible the enrichment and/or summarisation of transaction or event data with master or reference data. Furthermore many of the patterns used in data warehousing and master data management are inherent in Kafka as you can represent the current state of an object as well as the complete change history of that object (in other words change data capture and associated slowly changing dimensions from one inbound stream).

Data is acquired from source systems either in real time or as a scheduled extract process, in either case the data is presented to Kafka as a stream.

The Kafka Avro Schema Registry provides a systematic contract with source systems which also serves as a data dictionary for consumers supporting schema evolution with backward and forward compatibility. Data is retained on the Kafka platform for a designated period of time (days or weeks) where it is available for applications and processes to consume - these processes can include data summarisation or sliding window operations for reporting or notification, or data integration or datamart building processes which sink data to other systems - these could include relational or non-relational data stores.

Real time applications can be built using the KStreams API and emerging tools such as KSQL can be used to provide a well-known interface for sampling streaming data or performing windowed processing operations on streams. Structured Streaming in Spark or Spark Streaming in its original RDD/DStream implementation can be used to prepare and enrich data for machine learning operations using Spark ML or Spark MLlib.

In addition, data sinks can operate concurrently to sink datasets to S3 or Google Cloud Storage or both (multi cloud - like real time analytics - is something which is talked about more than it’s implemented…).

In the Streaming Data Warehouse architecture Kafka is much more than a messaging platform it is a distributed data platform, which could easily replace major components of a legacy (or even a modern) data architecture.

It just takes a little imagination…