Skip to main content

Pre Computation

Caching is a common technique, especially with HTTP as it is made so easy. However pre computation is an alternative that can be used to reduce failures as well as speed up processing and response times.

Caching Example

Assume a list of countries to be displayed on the UI. These are often stored in one logical place, the database. A remote call is issued to query the database and return the results. The results are then manipulated and inserted into the UI. Repeat calls will then be cached for some period by the web server and/or proxy.

Pre Computed Example

As part of the build process have the same query performed, dynamically building up the result set. Using a templating language modify a base source file which simply inserts the dynamic result set. The end result of this would be a source file containing a collection of countries as if you had hardcoded the values. The difference is these values are pulled from a single source of truth as part of the pre build step.

In a statically compiled language you would have compile time safety after this file is generated. Regardless a simple suite of tests to ensure the collection is not empty or badly formed would be beneficial.

Once the deploy is complete all queries to retrieve the collection of countries would be performed by the pre computed collection. This technique works regardless of language due to the simplicity of storing a collection of items in a literal array or hashtable. For content that changes regularly you can use a separate content deploy which simply deploys any changes to content.

Pre computation works for even what appears to be dynamic content. Article submission sites, e-commerce or wikis could all be developed using pre computation.

Use punch outs for anything that varies based on user or context. Javascript is the natural choice for inserting this dynamic content. This advice flies in the face of much of the direction the modern web is heading. However the benefits of reduced remote calls, fast responses and less moving parts should not be under estimated.

Naturally pre computation will not work in areas where content is highly dynamic or specific to users. Single page applications, social media streams and the like are better suited to dynamic content cached where possible. Additionally adjusting a system to handle content deploys is not something that can be achieved lightly. As the build and deploy process must accommodate these changes, pre computation is usually required to be thought of up front or require some rework to introduce.


Popular posts from this blog

Constant Object Anti Pattern

Most constants are used to remove magic numbers or variables that lack context. A classic example would be code littered with the number 7. What does this refer to exactly? If this was replaced with DaysInWeek or similar, much clarity is provided. You can determine that code performing offsets would be adding days, rather than a mysterious number seven.Sadly a common pattern which uses constants is the use of a single constant file or object. The beauty of constants is clarity, and the obvious fact such variables are fixed. When a constant container is used, constants are simply lumped together. These can grow in size and often become a dumping ground for all values within the application.A disadvantage of this pattern is the actual value is hidden. While a friendly variable name is great, there will come a time where you will want to know the actual value. This forces you to navigate, if only to peek at the value within the constant object. A solution is to simple perform a refactor …

Three Steps to Code Quality via TDD

Common complaints and problems that I've both encountered and hear other developers raise when it comes to the practice of Test Driven Development are: Impossible to refactor without all the tests breakingMinor changes require hours of changes to test codeTest setup is huge, slow to write and difficult to understandThe use of test doubles (mocks, stubs and fakes is confusing)Over the next three posts I will demonstrate three easy steps that can resolve the problems above. In turn this will allow developers to gain one of the benefits that TDD promises - the ability to refactor your code mercifully in order to improve code quality.StepsStop Making Everything PublicLimit the Amount of Dependencies you Use A Unit is Not Always a Method or ClassCode quality is a tricky subject and highly subjective, however if you follow the three guidelines above you should have the ability to radically change implementation details and therefore improve code quality when needed.

DRY vs DAMP in Tests

In the previous post I mentioned that duplication in tests is not always bad. Sometimes duplication becomes a problem. Tests can become large or virtually identically excluding a few lines. Changes to these tests can take a while and increase the maintenance overhead. At this point, DRY violations need to be resolved.SolutionsTest HelpersA common solution is to extract common functionality into setup methods or other helper utilities. While this will remove and reduce duplication this can make tests a bit harder to read as the test is now split amongst unrelated components. There is a limit to how useful such extractions can help as each test may need to do something slightly differently.DAMP - Descriptive and Meaningful PhrasesDescriptive and Meaningful Phrases is the alter ego of DRY. DAMP tests often use the builder pattern to construct the System Under Test. This allows calls to be chained in a fluent API style, similar to the Page Object Pattern. Internally the implementation wil…