Capacity Planning

One of the most important challenges that any enterprise business will face when deploying an application across a distributed network infrastructure, is knowing how much WAN network bandwidth is required to support business user response-time performance objectives. Traditionally, organisations without complex performance testing tools, have either estimated bandwidth requirements or taken a "suck it and see" approach, usually resulting in either inadequate capacity, or wasted over-capacity.

Diagnosys, through its Application Profiling service, can offer a simpler, more intelligent approach.

Once the application has been profiled, and a baseline model of the main transactions obtained, we can then perform a number of "What-If?" analyses on the data to provide predictive analysis of response-time performance under different LAN/WAN configurations. The wide-ranging performance characteristics of different applications, result in widely varying performance profiles under different LAN/WAN deployment configurations. The application profiling service provides a very effective way to quickly and accurately understand how the transaction response-time any n-tiered TCP-IP application will vary with differing values of network bandwidth, latency, or load.

The following screen-shot illustrates an example of a response-time prediction for a database query transaction running between a client and server.  The top (green) bar is the baseline response-time performance with all client-server tiers connected via a 100Mbps LAN, with minimal network latency and load.  The following graph bars reveal the impact on response-time performance once bandwidth is restricted (in this case at 64kbps, 128kbps, and 2Mbps).

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The following alternative predictive analysis, reveals how sensitive the application is to varying values of end-to-end network latency (50, 100, 200 ms), together with increasing network bandwidth (from 64kbps to 1.5Mbps).

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Both of these analyses reveal how sensitive the application is to network bandwidth and latency, and provides a very accurate guide as to what the optimum value of network bandwidth is required to hit a required response-time performance target.

In many cases, the predictions reveal that, in its current state, no matter how much bandwidth is applied, the application will never meet the required level of performance specified by the business. In this case, changes will need to be made within the application itself, so as to change its baseline performance profile, and its behaviour when deployed across a WAN. The information contained with the application profiling report will provide clues to the application developers, DBA's and/or technical architects as to what changes to the application code are required to meet the response-time performance objectives. Typical examples of such issues, include database queries that fetch data on a row-by-row basis across the WAN, instead of implementing more efficient  server-side stored-procedure queries.

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