Introduction

In a previous blog post we introduced the Spring Insight module that's part of SpringSource's tc Server developer edition and gives you, well, insight into what's taking up the time to process requests in your applications. Insight does this by instrumenting your application at load time using AspectJ: a single call to your application will result in a so-called trace consisting of various operations, and for each of these operations it's measured how long it takes to execute. An operation can provide additional details: for example, when sending a query to a database using a JDBC Connection the actual SQL statement including prepared statement bindings will be stored in the operation.

Spring Insight is not a profiler: it doesn't create operations for each and every little thing that happens, but only for 'significant' events, like a Spring-MVC controller invocation, the start of a transaction or communication with a database. These events are called 'operations'. It does allow assigning operations to so-called endpoints. An endpoint could be a controller method, or a method on a class annotated with one of Spring's stereotype annotations like @Service or @Repository for example. For these endpoints Insight can provide statistics across traces, so that you can measure the health of these endpoints during the lifespan of your application based on configurable thresholds.

Insight's plugin model

Spring Insight consists of a core plus a set of plugins that are shipped with the tool. These plugins define the actual operations and endpoints that Insight knows about and exposes. One of the nice things about Spring Insight is that the plugins use a public API that's not restricted to the built-in plugins: you can build your own plugins to teach the tool new tricks.

Although you could do this on a per-application basis to expose metrics relevant to your particular app, you wouldn't usually write a dedicated plugin for that. Insight already exposes several application-level methods as operations if they're part of your stereotype-annotated Spring beans, and you can use their set of annotations to expose additional application-specific operations and endpoints easily .

Plugins are much more useful for framework developers: their framework might contain several methods that would be interesting to expose as Insight operations or even endpoints to show users what the framework is doing and how long that takes. Earlier this year, that's exactly what we did for the Axon CQRS framework that's being developed within Trifork.

This blog briefly discusses the plugin's implementation. All source code has been added to the Axon Framework itself and is available on Github.

Update:
After publishing this blog entry, VMware has contacted  us to host the source code for this plugin in their public GitHub repository, so that the plugin can be shipped out-of-the-box with the Spring Insight distribution. That means that the plugin sources are no longer found under the Axon repository. The link above has been updated to reflect this change.

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