Optimizing Java by Unknown

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Capacity Planning Test

Capacity planning tests bear many similarities to stress tests, but they are a distinct type of test. The role of a stress test is to find out what the current system will cope with, whereas a capacity planning test is more forward-looking and seeks to find out what load an upgraded system could handle.

For this reason, they are often carried out as part of a scheduled planning exercise, rather in response to a specific event or threat.

Degradation Test

This type of test is also known as a Partial Failure Test. The general discussion of resilience and fail-over testing is outside the scope of this book, but suffice it to say that in the most highly regulated and scrutinized enivronments (including banks and financial institutions), fail-over and recovery testing is taken extremely seriously and is usually planned in meticulous depth.

For our purposes, the only type of resilience test we consider is the degradation test. The basic approach to this test is to see how the system behaves when a component or entire subsystem suddenly loses capacity whilst the system is running at simulated loads equivalent to usual production volumes. Examples could be application server clusters that suddenly lose members, databases that suddenly lose RAID disks or network bandwidth that suddenly drops.

Key observables during a degradation test include the transaction latency distribution and throughput.

One particularly interesting subtype of Partial Failure Test is known as the Chaos Monkey. This is named after a project at Netflix that was undertaken to verify the robustness of their infrastructure.

The idea behind Chaos Monkey is that in a truly resilient architecture, the failure of a single component should not have the ability to cause a cascading failure or to cause meaningful impact on the overall system.

Chaos Monkey attempts to demonstrate this by randomly killing off live processes that are actually in use in the production environment.

In order to successfully implement Chaos Monkey type systems, an organisation must have the highest levels of system hygiene, service design and operational excellence. Nevertheless, it is an area of interest and aspiration for an increasing number of companies and teams.

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