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Recently, I have been involved in an effort which required migrating a database with millions of rows from MySQL to Azure CosmosDB. Those who are new to CosmosDB, it is a Microsoft’s globally distributed, multi-model database service. The good thing about CosmosDB is that it provides data access using the familiar API’s in form of SQL, MongoDB, Cassandra etc. We used the MongoDB driver for our use-case, so essentially it was a RDBMS to NOSQL...

I have been playing with Apple’s CreateML. Specifically, I have been following Apple’s tutorial on creating text classification models The exact code as described in article doesn’t work, atleast on OSX 10.14 Mojave. The snippet I have been using is: import Cocoa import CreateML import NaturalLanguage let data = try MLDataTable(contentsOf: URL(fileURLWithPath: "/Users/madhur/Desktop/iOS/ML/twitter-sanders-apple3.csv")) let (trainingData, testingData) = data.randomSplit(by: 0.8, seed: 5) let sentimentClassifier = try MLTextClassifier(trainingData: trainingData, textColumn: "text", labelColumn: "class") The last line throws...

Recently, one of my Macbook Pro 2014 model started showing this information on battery usage: Naturally, it got me worried as I had lot of code and data which was not backed up. However, at the same time I was curious to know how Apple is able to determine the degradation in battery health. Is it a function of age, discharge / charging time OR something else? Upon further debugging, turns it its a function...

I got thrown up with some more tasks to perform on shell. First was to extract numbers from long list of text. For ex, you have text as : [ NumberLong(90), NumberLong(123), NumberLong(218), NumberLong(221), NumberLong(294), NumberLong(317), NumberLong(319), NumberLong(322), NumberLong(328), NumberLong(344), NumberLong(348) ] To simple extract numbers from this file, we’ll use pcregrep command to capture the regex group and output it. #!/bin/bash cat input.txt | pcregrep -o1 -i '([0-9]+)' > output.txt Second was to compare...

Recently, I was required to generate multiple UUID’s and pass onto HTTP request as a paremeter. I thought of using Python or Node.js for this purpose, but thought why not use a plain old shell. But, is there a way to generate UUID in shell? Turns out, there is using uuidgen command which works on both Linux and MacOS. Hence, using the power of another command called seq, and xargs we can achieve many powerful...

I have always been fan of well assembled desktop systems. Its a joy to carefully pick each component of your personal computer and assemble it to pick best performance. The current rig which I use is listed here on PCPartPicker It is also very important to continously monitor the performance of such system so as to make sure they are running in optimum systems. Especially important is CPU and GPU temperatures. With latest software and...

In a well designed backend application, which makes calls to other HTTP services, it is very important to configure appropriate timeout values. In event of a service failure, a large timeout value can cause threads on the application to keep waiting for service to respond and may ultimately run out of threads which could have been used for doing other work. Otherwise, low timeout value can cause genuine requests to be aborted which would have...

The sample code below is available in my github repo Let’s face it, HTTP network calls can face intermittently. Even if you best configure the Linux Operating System, the TCP/IP networking stack and the best possible private / public cloud networks, failures are inevitable. Sometimes, the reason can be dropped packets at router / NIC or could be any issue in networking stack. For any well designed backend application, it is imperative to design for...

In this post, we will look at tools to test remote connectivity in Linux. With increasing usage of firewalls, server hardening due to cyber attacks, it becomes important to determine appropriate connectivity between two hots. Note that, we are looking for connectivity tests w.r.t. server systems such as databases, application servers etc. Organizations having multiple datacenters, systems running in private / public clouds, accessing vendor partner systems, its important to have a know how to...

Classloaders are an important concept for every engineer to be aware of. Classloaders are basic building blocks of Containers like Tomcat. Suppose, we have written a java application and have a singleton instance, we might say its singleton across JVM. Wrong. Its not singleton across JVM, its a singleton across classloader. The same application can be deployed in a container like Tomcat, as two different application. In that case, there will be 2 copies of...