Skip to main content

The Joy of Debugging

For a long while now, my demo transit application hasn't been picking up new articles from the web - leaving the home page looking quite stale between deployments.

Earlier this week I added extra logging to capture counts of different kinds of articles, and noticed this morning that new articles were only found the first time the parsers run. After reviewing the simple logic for determining which articles are new, I noticed the cache implementation problem.

I had implemented a crude cache using a hash map, but apparently forgot to write the cache expiration logic. When the parsers went to look at news listing pages, the cache was returning a stale block of content rather than fetching the new content from the internet. I was so sure I wrote that expiration logic! So things are all fixed up and I'm going to be verifying the fix over the next few days.

Nothing quite beats the feeling of finding a simple explanation for a pesky bug.
Labels:
Location: Bay Ridge, Brooklyn, NY, USA

Comments

Post a Comment

Popular posts from this blog

ReactJS, NPM and Maven

I'm just starting to get into working with ReactJS, Facebook's open source rendering framework. My project uses SpringBoot for annotation-driven dependency injection and MVC. I thought it would be great if I could use a bit of ReactJS to enhance the application. If you're looking for a basic conceptual intro, I recommend ReactJS for Stupid People and of course the official documentation  is quite good. In full disclosure, I still have no idea how to do "flux" yet. As an experienced Java backend developer, I'm pretty decent at hacking Maven builds - which is precisely what this blog post is going to be about. First, a word about how React likes to be built. Like many front-end tools, there is a toolkit for the node package manager (NPM). From the command prompt, one might run npm install -g react-tools  which installs the jsx command. The  jsx  command provides the ability to transform JSX syntax into ordinary JavaScript, which is precisely what I want. O
16 comments
Read more

Solved: Unable to Locate Spring Namespace Handler

I attempted to run a Spring WebMVC application, and when starting up the application complained that it didn't know how to handle the MVC namespace in my XML configuration. The project runs JDK 7 and Spring 4.0.6 using Maven as the build system. The following is my XML configuration file: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans"        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"        xmlns:mvc="http://www.springframework.org/schema/mvc"        xsi:schemaLocation="         http://www.springframework.org/schema/beans         http://www.springframework.org/schema/beans/spring-beans.xsd         http://www.springframework.org/schema/mvc         http://www.springframework.org/schema/mvc/spring-mvc.xsd">          <mvc:annotation-driven/>      </beans> I have a few more beans than this, but their details aren't especially relevant
1 comment
Read more

Spark Cassandra Connector Tip

We're using Databricks as our provider for Spark execution, and we've been struggling to get the Spark Cassandra connector to work outside of the local development environment. The connector was attempting to connect to 127.0.0.1 even though we were passing the new host information into the getOrCreate(..) call. After working with Ganesh at Databricks support, we figured it out. The realization is that in Databricks, calls to getOrCreate() from a fat jar don't create a new SparkContext object. Thus, the configuration passed in gets ignored. If you want to update the Cassandra host information for the connector, you must update it after  the call to getOrCreate() instead. Add the configuration directly to the context and you'll be good to go!
Post a Comment
Read more