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SQL: Counting Groups of Rows Sharing Common Column Values


In this post, I focus on using simple SQL SELECT statements to count the number of rows in a table meeting a particular condition with the results grouped by a certain column of the table. These are all basic SQL concepts, but mixing them allows for different and useful representations of data stored in a relational database. The specific aspects ...

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Iterate over all keys in a Redis Cluster


Redis provides a neat command to iterate over all keys on a node. It’s the SCAN command that is used to scan over keys and to return a cursor to resume then the scanning from the cursor position. Complexity comes in when using Redis Cluster. In the previous scenario, all keys are located on one Redis node. With Redis Cluster ...

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12 Awesome Spring Data Tutorials to Kick-Start your Data Projects


Spring Data’s mission is to provide a familiar and consistent, Spring-based programming model for data access while still retaining the special traits of the underlying data store. It makes it easy to use data access technologies, relational and non-relational databases, map-reduce frameworks, and cloud-based data services. This is an umbrella project which contains many subprojects that are specific to a ...

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Docker meets Continuous Deployment


About one year ago I had my first contact with Docker. This new kid on the block promised to relieve our poor computers from installation of all tools, languages, dependencies and operating systems. Isolated run environments emerged on developers’ computers. While my ops teammates chose a more conservative approach, I started to use Docker with great joy. Despite many people ...

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Cohesion – The cornerstone of Software Design


Cohesion is one of the most important concepts in software design. Cohesion is at the core of the vast majority of good design principles and patterns out there, guiding separation of concerns and maintainability. The term cohesion (alongside coupling) was first introduced by Larry Constantine in the late 60s as part of Structured Design and later published in more details ...

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Give Enterprise APIs Visibility With Swagger And GrokOla


The Keyhole Labs team is excited to announce that GrokOla now offers Swagger integration. GrokOla users can now upload Swagger JSON files into GrokOla to have all API documentation centralized, searchable, and accessible from within their private GrokOla instance.             This is the example Swagger UI Petstore server loaded into and accessible from GrokOla. Info: ...

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Getting Started with rkt


This February, CoreOS announced that their rkt container runtime had graduated to version 1.0. rkt has come a long way since its initial announcement in December 2014, so now’s a good time to take a closer look and consider how it fits into the rapidly changing container ecosystem. This article is intended for people who are new to rkt but ...

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8 Steps For Effective User Stories


As  a developer/tester I want to understand the user story So I can build/test it correctly. Mind you, this is a terrible user story. What does “understand” mean? And what is the acceptance criteria for “build it correctly”? Life is messy, and the “As a…” template doesn’t always help. You can over-cram it to make it detailed, or over-abstract it, ...

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Equality vs Identity?


When storing objects in a Set, it is important that the same object can never be added twice. That is the core definition of a Set. In java, two methods are used to determine whether two referenced objects are the same or if they can both exist in the same Set; equals() and hashCode(). In this article I will explain ...

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How to Log in Apache Spark


An important part of any application is the underlying log system we incorporate into it. Logs are not only for debugging and traceability, but also for business intelligence. Building a robust logging system within our apps could be use as a great insights of the business problems we are solving. Log4j in Apache Spark Spark uses log4j as the standard ...

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