Skip to main content

[Software metrics] Mean Time Between Failure - MTBF

MTBF - Meantime between failure
In today post I would like to talk about a software metric that can give us information related to the quality of our product and how stable it is – Meantime Between Failure.
This metric measure the time interval between the moment when a failure was fixed (and the system is stable) until the moment when a new failure is detected. We could say that this metric measure the time interval when the system is up and running.
Using this metric, we can obtain to important information related to our system:
  • How stable our system is
  • When the next failure will occur

I think that the second point is pretty interesting, especially when we have a system in production. Theoretically, MTBF could tell to the operational and maintenance team when next fail over will have – in this way they can be prepared for it.
MTBF can be calculated in different ways, the most simple formulate for it is the sum of all the time intervals when the system didn’t had a failure divided by the numbers of failure.

In a real product, we expect to have issues open all the time, even if we don’t like this. Because of this we need to define what kind of failures we measure (for example the severity level of them). We should measure the MTBF for critical failures (system is down, clients cannot use application anymore and so on). In a normal product, this kind of failures I would expect to be counted when we would calculate the MTBF.
I calculated the MTBF for a web application that is hosted on Windows Azure from 2011. The MTBF for this web application is around 10 months. The cause of the failures that we had until now was caused by:
  • A Windows Azure Service was down and we didn't had a fail over solution for it
  • Client infrastructure was down and we our web application depended on that service

In this post we saw a software metric that can be used with success when we need to predict when the next time when we’ll have a failure is. This metric can be calculated very easily and can help us to understand how stable our system is.

I invite you to calculate this metric for your own system and see what values you get.


Popular posts from this blog

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…

GET call of REST API that contains '/'-slash character in the value of a parameter

Let’s assume that we have the following scenario: I have a public HTTP endpoint and I need to post some content using GET command. One of the parameters contains special characters like “\” and “/”. If the endpoint is an ApiController than you may have problems if you encode the parameter using the http encoder.
using (var httpClient = new HttpClient()) { httpClient.BaseAddress = baseUrl; Task<HttpResponseMessage> response = httpClient.GetAsync(string.Format("api/foo/{0}", "qwert/qwerqwer"))); response.Wait(); response.Result.EnsureSuccessStatusCode(); } One possible solution would be to encode the query parameter using UrlTokenEncode method of HttpServerUtility class and GetBytes method ofUTF8. In this way you would get the array of bytes of the parameter and encode them as a url token.
The following code show to you how you could write the encode and decode methods.