SparkSession Versus SparkContext

Abhishek Baranwal explains the differences between the SparkSession object and the SparkContext object when writing Spark code:

Prior to spark 2.0, SparkContext was used as a channel to access all spark functionality. The spark driver program uses sparkContext to connect to the cluster through resource manager.

SparkConf is required to create the spark context object, which stores configuration parameters like appName (to identify your spark driver), number core and memory size of executor running on worker node.

In order to use API’s of SQL, Hive, and Streaming, separate context needs to be created.

Read on to see where SparkSession fits in.

Hadoop + SQL Server In 2019

Travis Wright shows off a big part of what the SQL Server team has been working on the last couple of years:

SQL Server 2019 big data clusters provide a complete AI platform. Data can be easily ingested via Spark Streaming or traditional SQL inserts and stored in HDFS, relational tables, graph, or JSON/XML. Data can be prepared by using either Spark jobs or Transact-SQL (T-SQL) queries and fed into machine learning model training routines in either Spark or the SQL Server master instance using a variety of programming languages, including Java, Python, R, and Scala. The resulting models can then be operationalized in batch scoring jobs in Spark, in T-SQL stored procedures for real-time scoring, or encapsulated in REST API containers hosted in the big data cluster.

SQL Server big data clusters provide all the tools and systems to ingest, store, and prepare data for analysis as well as to train the machine learning models, store the models, and operationalize them.
Data can be ingested using Spark Streaming, by inserting data directly to HDFS through the HDFS API, or by inserting data into SQL Server through standard T-SQL insert queries. The data can be stored in files in HDFS, or partitioned and stored in data pools, or stored in the SQL Server master instance in tables, graph, or JSON/XML. Either T-SQL or Spark can be used to prepare data by running batch jobs to transform the data, aggregate it, or perform other data wrangling tasks.

Data scientists can choose either to use SQL Server Machine Learning Services in the master instance to run R, Python, or Java model training scripts or to use Spark. In either case, the full library of open-source machine learning libraries, such as TensorFlow or Caffe, can be used to train models.

Lastly, once the models are trained, they can be operationalized in the SQL Server master instance using real-time, native scoring via the PREDICT function in a stored procedure in the SQL Server master instance; or you can use batch scoring over the data in HDFS with Spark. Alternatively, using tools provided with the big data cluster, data engineers can easily wrap the model in a REST API and provision the API + model as a container on the big data cluster as a scoring microservice for easy integration into any application.

I’ve wanted Spark integration ever since 2016 and we’re going to get it.

Writing To Elasticsearch With Spark Streaming

Anuj Saxena has an example of writing data from a Spark Streaming pipeline out to Elasticsearch:

There’s been a lot of time we have been working on streaming data. Using Apache Spark for that can be much convenient. Spark provides two APIs for streaming data one is Spark Streaming which is a separate library provided by Spark. Another one is Structured Streaming which is built upon the Spark-SQL library. We will discuss the trade-offs and differences between these two libraries in another blog. But today we’ll focus on saving streaming data to Elasticseach using Spark Structured Streaming. Elasticsearch added support for Spark Structured Streaming 2.2.0 onwards in version 6.0.0 version of “Elasticsearch For Apache Hadoop” dependency. We will be using these versions or higher to build our sbt-scala project.

Click through for an example.

Databricks Delta Now Available On Azure

Cihan Biyikoglu and Singh Garewal announce the availability of Databricks Delta on Azure Databricks:

Using an innovative new table design, Delta supports both batch and streaming use cases with high query performance and strong data reliability while requiring a simpler data pipeline architecture:

Increased query performance – Able to deliver 10 to 100 times faster performance than Apache Spark(™) on Parquet through the use of key enablers such as compaction, flexible indexing, multi-dimensional clustering and data caching.

Improved data reliability – By employing ACID (“all or nothing”) transactions, schema validation / enforcement, exactly once semantics, snapshot isolation and support for UPSERTS and DELETES.

Reduced system complexity – Through the unification of batch and streaming in a common pipeline architecture – being able to operate on the same table also means a shorter time from data ingest to query result. Schema evolution provides the ability to infer schema from input data making it easier to deal with changing business needs.

The Azure version of Databricks is quickly reaching parity with the classic AWS-hosed version.

Flint: Time Series With Spark

Li Jin and Kevin Rasmussen cover the concepts of Flint, a time-series library built on Apache Spark:

Time series analysis has two components: time series manipulation and time series modeling.

Time series manipulation is the process of manipulating and transforming data into features for training a model. Time series manipulation is used for tasks like data cleaning and feature engineering. Typical functions in time series manipulation include:

  • Joining: joining two time-series datasets, usually by the time
  • Windowing: feature transformation based on a time window
  • Resampling: changing the frequency of the data
  • Filling in missing values or removing NA rows.

Time series modeling is the process of identifying patterns in time-series data and training models for prediction. It is a complex topic; it includes specific techniques such as ARIMA and autocorrelation, as well as all manner of general machine learning techniques (e.g., linear regression) applied to time series data.

Flint focuses on time series manipulation. In this blog post, we demonstrate Flint functionalities in time series manipulation and how it works with other libraries, e.g., Spark ML, for a simple time series modeling task.

Basho went all-in on a time-series product for Riak and it did not work out well for them.  I’ll be curious to see if Flint has more staying power.

ElasticMapReduce And RStudio

Tanzir Musabbir demonstrates how to set up Amazon ElasticMapReduce to include an RStudio edge node:

RStudio Server provides a browser-based interface for R and a popular tool among data scientists. Data scientist use Apache Spark cluster running on  Amazon EMR to perform distributed training. In a previous blog post, the author showed how you can install RStudio Server on Amazon EMR cluster. However, in certain scenarios you might want to install it on a standalone Amazon EC2 instance and connect to a remote Amazon EMR cluster. Benefits of running RStudio on EC2 include the following:

  • Running RStudio Server on an EC2 instance, you can keep your scientific models and model artifacts on the instance. You might have to relaunch your EMR cluster to meet your application requirements. By running RStudio Server separately, you have more flexibility and don’t have to depend entirely on an Amazon EMR cluster.
  • Installing RStudio on the master node of Amazon EMR requires sharing of resources with the applications running on the same node. By running RStudio on a standalone Amazon EC2 instance, you can use resources as you need without having to share the resources with other applications.
  • You might have multiple Amazon EMR clusters in your environment. With RStudio on Edge node, you have the flexibility to connect to any EMR clusters in your environment.

There is one major difference between running RStudio Server on an Amazon EMR cluster vs. running it on a standalone Amazon EC2 instance. In the latter case, the instance needs to be configured as an Amazon EMR client (or edge node). By doing so, you can submit Apache Spark jobs and other Hadoop-based jobs from an instance other than EMR master node.

Click through for detailed, step-by-step instructions on how to do this.

Databricks Cluster-Scoped Init Scripts

Aayush Bhasin shares some background on a Databricks intern project, adding cluster-scoped initialization scripts to Databricks clusters:

One of the biggest pain points for customers used to be that init scripts for a cluster were not part of the cluster configuration and did not show up in the User Interface. Because of this, applying init scripts to a cluster was unintuitive, and editing or cloning a cluster would not preserve the init script configuration. Cluster-scoped init scripts addressed this issue by including an ‘Init Scripts’ panel in the UI of the cluster configuration page, and adding an ‘init_scripts’ field to the public API. This also allows init scripts to take advantage of cluster access control.

Read on to see how Aayush & co. solved this issue.

Databricks UDF Performance Testing

Tristan Robinson shares some performance comps for different Azure Databricks scenarios:

I’ve recently been spending quite a bit of time on the Azure Databricks platform, and while learning decided it was worth using it to experiment with some common data warehousing tasks in the form of data cleansing. As Databricks provides us with a platform to run a Spark environment on, it offers options to use cross-platform APIs that allow us to write code in Scala, Python, R, and SQL within the same notebook. As with most things in life, not everything is equal and there are potential differences in performance between them. In this blog, I will explain the tests I produced with the aim of outlining best practice for Databricks implementations for UDFs of this nature.

Scala is the native language for Spark – and without going into too much detail here, it will compile down faster to the JVM for processing. Under the hood, Python on the other hand provides a wrapper around the code but in reality is a Scala program telling the cluster what to do, and being transformed by Scala code. Converting these objects into a form Python can read is called serialisation / deserialisation, and its expensive, especially over time and across a distributed dataset. This most expensive scenario occurs through UDFs (functions) – the runtime process for which can be seen below. The overhead here is in (4) and (5) to read the data and write into JVM memory.

Click through for the results.  Looks like Python barely beat out Scala for the #1 position, but Scala was a little faster than Python in-class (e.g., the Scala program with a Scala SQL UDF was a little bit faster than the Python equivalent).

Kalman Filters With Spark And Kafka

Konur Unyelioglu goes deep into Kalman filters:

In simple terms, a Kalman filter is a theoretical model to predict the state of a dynamic system under measurement noise. Originally developed in the 1960s, the Kalman filter has found applications in many different fields of technology including vehicle guidance and control, signal processing, transportation, analysis of economic data, and human health state monitoring, to name a few (see the Kalman filter Wikipedia page for a detailed discussion). A particular application area for the Kalman filter is signal estimation as part of time series analysis. Apache Spark provides a great framework to facilitate time series stream processing. As such, it would be useful to discuss how the Kalman filter can be combined with Apache Spark.

In this article, we will implement a Kalman filter for a simple dynamic model using the Apache Spark Structured Streaming engine and an Apache Kafka data source. We will use Apache Spark version 2.3.1 (latest, as of writing this article), Java version 1.8, and Kafka version 2.0.0. The article is organized as follows: the next section gives an overview of the dynamic model and the corresponding Kalman filter; the following section will discuss the application architecture and the corresponding deployment model, and in that section we will also review the Java code comprising different modules of the application; then, we will show graphically how the Kalman filter performs by comparing the predicted variables to measured variables under random measurement noise; we’ll wrap up the article by giving concluding remarks.

This is going on my “reread carefully” list; it’s very interesting and goes deep into the topic.

Databricks Runtime 4.3 Released

Todd Greenstein announces Databricks Runtime 4.3:

In addition to the performance improvements, we’ve also added new functionality to Databricks Delta:

  • Truncate Table: with Delta you can delete all rows in a table using truncate.  It’s important to note we do not support deleting specific partitions.  Refer to the documentation for more information: Truncate Table

  • Alter Table Replace columns: Replace columns in a Databricks Delta table, including changing the comment of a column, and we support reordering of multiple columns.   Refer to the documentation for more information: Alter Table

  • FSCK Repair Table: This command allows you to Remove the file entries from the transaction log of a Databricks Delta table that can no longer be found in the underlying file system. This can happen when these files have been manually deleted.  Refer to the documentation for more information: Repair Table

  • Scaling “Merge” Operations: This release comes with experimental support for larger source tables with “Merge” operations. Please contact support if you would like to try out this feature.

Looks like a nice set of reasons to upgrade.

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