Regressions are one of the risks of our profession. Fortunately, we can limit the risk thanks to different testing strategies. One of them are regression tests that we can use to check whether the modified data processing logic didn't introduce the regressions simply by comparing two datasets.
In one of my previous posts I presented how to add a custom optimization to Apache Spark SQL. It was not a good moment to deep delve into the topic because of its complexity. That's why I will try to do a better job here by showing the API of native optimizations.
One of data governance goals is to ensure data consistency across different producers. Unfortunately, very often it's only a theory and especially when the data format is schemaless. It's why the data exploration is an important step in the process of data pipeline definition. In this post I wanted to do a small exercise and check how Apache Spark SQL behaves with inconsistent data.
Apache Spark 2.4.0 brought a lot of internal changes but also some new features exposed to the end users, as already presented high-order functions. In this post, I will present another new feature, or rather 2 actually, because I will talk about 2 new SQL functions.
Some time ago I was thinking whether Apache Spark provides the support for auto-incremented values, so hard to implement in distributed environments After some research, I almost found what I was looking for - monotonically increasing id. In this post, I will try to explain why "almost".
In November 2018 bithw1 pointed out to me a feature that I haven't used yet in Apache Spark - custom optimization. After some months consacred to learning Apache Spark GraphX, I finally found a moment to explore it. This post begins a new series about Apache Spark customization and it covers the basics, i.e. the 2 available methods to add the custom optimizations.
Apache Avro became one of the serialization standards, among others because of its use in Apache Kafka's schema registry. Previously to work with Avro files with Apache Spark we needed Databrick's external package. But it's no longer the case starting from 2.4.0 release where Avro became first-class citizen data source.
The series about the features introduced in Apache Spark 2.4.0 continues. Today's post will cover higher-order functions that you may know from elsewhere.
This post begins a new series dedicated to Apache Spark 2.4.0 features. The first covered topic will be bucket pruning.
Schemas are one of the key parts of Apache Spark SQL and its distinction point with old RDD-based API. When we deal with data coming from a structured data source as a relational database or schema-based file formats, we can let the framework to resolve the schema for us. But the things complicate when we're working with semi-structured data as JSON and we must define the schema by hand.
The code generated by Apache Spark for all the queries defined with higher-level concepts as SQL queries is the key to understand the processing logic performance. This post, started after a discussion on my Github, tries to explain some of the basics of code generation workflow.
Some weeks ago I've written a post about files with long lines impact on RDD-based processing. The post revealed the difficulty to process such files because of OOM errors. In this post I wanted to check how does it apply to Datasets.
Some months ago bithw1 posted an interesting question on my Github about multiple SparkSessions sharing the same SparkContext. If you have similar interrogations, feel free to ask - maybe it will give a birth to more detailed post adding some more value to the community. This post, at least, tries to do so by answering the question.
Some time ago on my Github bithw1 pointed out an interesting behavior of Hive integration on Apache Spark SQL. To not delve too much into details now, I can tell that the behavior was about not respected DataFrame schema. Our quick exchange ended up with an explanation but it also encouraged me to go much more into details to understand the hows and whys.
Apache Spark SQL provides advanced analytics features that we can find in more classical OLAP-based workloads. Below I'll explain one of them.
Most of RDBMS are able to store JSON documents in columns of JSON-like type. One of them is PostgreSQL that can keep JSONs in one of 2 columns (JSON or JSONB) and that natively enables querying of JSON document attributes. As we'll see below, with a little bit of effort we can implement similar behavior in Apache Spark SQL.
Nested data structure is very useful in data denormalization for Big Data needs. It avoids joins that we could use for several related and fully normalized datasets. But processing such data structures is not always simple. Fortunately Apache Spark SQL provides different utility functions helping to work with them.
One of previous posts in SQL category presented window functions that can be used to compute values per grouped rows. These analytics functions are also available in Apache Spark SQL.
Some recent posts covered important Spark SQL options for RDBMS: partitioning and write modes. However they're not the only ones available for this data storage.
Some months ago I presented save modes in Spark SQL. However, this post was limited to their use in files. I was quite surprised to observe some specific behavior of them for RDBMS sinks. Especially for SaveMode.Overwrite.
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