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Hive sits on top of HDFS (the Hadoop Distributed File System). It reads the files that reside onto HDFS into a specified schema (column names & types), which we can then query and interact with. One such way we may interact with Hive is using Apache Spark. When we write to HDFS, we often end […]
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Performance is a major concern when you’re working in a distributed environment with a massive amount of data. I’ve discussed Spark performance in quite a lot of detail before here and here. Today I am going to talk specifically about percentiles. Because, calculating percentiles over large distributed datasets is a mammoth task. You will likely […]
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This article covers a less than orthodox method for handling resource constraints in your PySpark code. Consider the below scenario. Here, we are loading data from four sources doing some joins & aggregations and producing an output. The problem is, we keep getting timeout errors because the data is just so large. After tuning the […]
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Data Skew is a real problem in Spark. It seems like the sort of thing which should be solved automatically by the job manager but unfortunately, it isn’t. Skew is where we have a given partition which contains a huge amount more data than others – leaving one executor to process a lot of data, […]
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Apache Spark provides us with a framework to crunch a huge amount of data efficiently by leveraging parallelism which is great! However, with great power, comes great responsibility; because, optimising your scripts to run efficiently, is not so easy. Within our scripts, we need to look to minimize the data we bring in; avoid UDF’s […]
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Window functions are incredibly useful. Within a single query, you can find out things which may have otherwise been tricky. In this article, I will cover all of the key window functions in Pyspark. First off, we need to define our dataframe – you can get the data to play along here. Now, we have […]
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Okay, so the first thing I should note is that you should avoid UDF’s (User Defined Functions) like the plague unless you absolutely have to; I have spoken about why that is here. Now that I’ve warned you, let’s talk about what a UDF is. A UDF is a User Defined Function, it’s a function […]
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When you’re dealing with tonnes of different datasources, issues crop up all the time: the datasource hasn’t been populated; the schema has changed; the schedule changes or the file format changes. The key with our jobs is to build in enough checks to at the very least warn us if something fails, so we can […]
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Welcome to this weeks Starter Sunday – which is where I cover off some basic concepts of Spark, Python or Hive. Today, we’re looking at selecting and filtering data from our dataframes in Spark, specifically, Pyspark. Select specific columns Below, we have a dataframe called df_select which will take just two columns from the dataframe […]
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In Spark Streaming, we have the concept of sources and sinks. A source is very much what you would expect it to be – it’s the source of the data we will be ingesting into our stream. A sink, is the destination for that data in the L part of the ETL process. Sources Looking […]
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Streaming applications need to be fault tolerant. They need to be able to cope with system failures, JVM crashes and all that sort of horrible stuff. To cope with that, Spark Streaming uses the concept of checkpointing. That is, it stores metadata about which files it’s processed so far – so if it fails, it […]
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In my last article, I showed an example of a Spark Streaming application for ingesting application log files. Today, I am going to cover off an overview of DStreams in Spark Streaming. In subsequent articles, we’ll really look in detail at some of the main Spark Streaming concepts. We can source data from loads of […]
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