Understanding a Postgres query plan
Posted on Apr 13, 2020
| 11 minutes
A query plan is a sequence of steps used by a database to access data. Being able to read a query plan is key to understanding the performance of an SQL query. While tuning a query we need to know how the rows are being fetched from the tables? Are the indexes being used? What is the cost of joining to tables? A query plan provides with an answer for all of these questions.
[Read More]
Database integration tests for a Spring application
Posted on Jan 12, 2019
| 6 minutes
Suppose you are tasked with writing tests for a Spring and Hibernate application. This application uses a mix of native queries, HQL or entity associations to fetch data from the database. If you choose to mock the DAO or entity layers, you leave a significant portion of the code untested. In such cases data integration tests can provide the most correct feedback. But you do you configure your application to run integration tests?
[Read More]
The small pleasures of programming
Posted on Sep 23, 2018
| 2 minutes
It’s not just pulling off a complex engineering feat that makes programmers love their jobs. There are small pleasures to be had even in your day to day tasks, if you look for them.
Seasoned programmers know the thrill of recognising the possibility to introduce an abstraction over duplication. A task as simple as renaming a variable can be the difference between obscurantism and lucidity. It’s the boy scout principle in action.
[Read More]
Representing natural numbers in lambda calculus
Posted on Nov 8, 2017
| 7 minutes
One of the joys of reading SICP is that apart from the main subject matter, we come across many tangential topics that are interesting in their own right. One such topic is mentioned in Exercise 2.6: Church numerals. Named after the mathematician Alonzo Church, Church numerals are a way of representing natural numbers in lambda calculus. But what is λ-calculus?
From a programming perspective, λ-calculus can be thought of as the smallest universal programming language.
[Read More]
Using thread dumps to analyse deadlocks
Posted on Oct 14, 2017
| 2 minutes
In a multi-threaded Java application, a deadlock occurs when two threads wait forever attempting to acquire locks that are held by each other. Here’s a simple example to simulate a deadlock: public class Deadlock { private Object lock1; private Object lock2; public Deadlock(Object lock1, Object lock2) { this.lock1 = lock1; this.lock2 = lock2; } public void methodA() { System.out.println("trying to acquire lock1 from - " + Thread.currentThread().getName()); synchronized (lock1) { someLongRunningTask(); methodB(); } } public void methodB() { System.
[Read More]
Setting up a JavaScript project in 2017
Posted on Jan 14, 2017
| 8 minutes
Creating a front-end JavaScript project can be a daunting task due to the sheer volume of choices available while deciding the tech stack. First, you need to decide the JavaScript framework or library for your project. Do you plan to use the latest ES2015 language features in your code? If yes, then you need a transpiler because your browser probably doesn’t support them yet. Then you require a bundling tool to get your code loaded in the browser.
[Read More]
Hystrix – a simple use case
Posted on Dec 5, 2016
| 2 minutes
Hystrix is a fault tolerance library that is very useful for managing failures in a distributed environment like microservices. Suppose we have a service A dependent on service B, which is in turn dependent on service C.
A -> B -> C Let’s say a call is made from A to B. To serve this request, B needs to call C but there’s a communication failure between them. If the call from B to C is wrapped in Hystrix mechanism, we prevent the failure being propagated to A.
[Read More]
Running time intensive operations in parallel with RxJava Observables
Posted on Sep 1, 2016
| 4 minutes
Recently I delved into the RxJava library. In this post I will demonstrate how RxJava Observables can be used to execute two long running tasks in parallel, so as to reduce their overall execution time.
While we can create threads for this purpose, an additional benefit of using Observables is that it provides a convenient way of collecting the results of the parallel tasks. With threads, this can get pretty complicated.
[Read More]
In case of any query, revert back to me
Posted on Aug 1, 2016
| 1 minutes
If you have ever worked in an office in India, you would have encountered the phrase “revert back” at the end of official emails. When people ask you to “revert back”, they are actually asking you to “reply back”. It is an Indian colloquialism and in fact people think that using this phrase makes them sound more formal!
Of course languages are used differently in different parts of the world. But I have always wondered in which scenario would asking someone to “revert back” be a doable request?
[Read More]
Logging with Spring AOP
Posted on Feb 12, 2016
| 3 minutes
Aspect oriented programming (AOP) is a way of separating the business login in your code from cross cutting concerns. What is a cross cutting concern?
Analogy time. A typical house has different rooms that have designated functions. We keep our stuff in the rooms where they make sense. The living room is an unlikely location for a dishwasher and a bathtub belongs in the bathroom. But the electric circuit runs throughout the house because it is not tied to the functionality of any specific room.
[Read More]