Tuesday, May 6, 2008

Capacity Planning - Planning the Processor Subsystem

Planning the processor subsystem for a database infrastructure is a straight forward task. Normally, all the high end servers will be using the latest available best processors. If all the individual servers are already loaded with the best the maximum supported number of best available processors, the way to increase the processing power is to increase the number of servers. These two ways of increasing processing power is explained in the sections below.
Scale-up vs. Scale-out
Scale up is the process of increasing the processing power of an already existing server either by adding more processors or by increasing the processing power of the processors. Scale out is the process of increasing the processing power of a database infrastructure by increasing the number of servers so that the load can be distributed among the different servers. Both these approaches have got their benefits and downsides.
Scale up is normally considered as a quick fix to resolve processor bottlenecks for database applications. With the arrival of hot swappable CPUs and databases supporting them, this approach doesn’t require little downtime and lesser overhead of planning. The major advantage is that, since it does not increase the number of servers, there is no extra overhead in terms of maintenance, monitoring, licensing etc.
Though scale up can be done easily as a quick fix for issues, it has its downsides. The major disadvantage is that there is always a maximum gain we can get by scaling up. This is because there are limitations for the maximum number of processors supported for a particular operating system as well as the RDBMS. Hence, scaling up cannot be considered as a permanent solution especially when the application is an ongoing growing application.
Scale out is normally considered as a permanent solution for increasing processing power. The most important advantage of this approach is the expandability. We can add more servers and make the application to use the newly added servers.
Since scale out is a more permanent solution, it requires a lot of planning and overhead. The most important disadvantage is that the application should be redesigned to make use of the multiple servers. This may not be an easy task for ongoing applications, and will be a costly affair. There are other disadvantages as well. These include the increased overhead of extra servers for maintenance, monitoring licensing etc.
We can decide whether to go for scale up or scale out depending upon the current situation of the application, and what is the future of the application.
Factors for Considerations
While selecting the processors, there are a few factors to be considered and see how they affect the application environment.
Ø Processor Architecture
Nowadays, processors are available in 32bit and 64bit architectures. We can decide which architecture our infrastructure requires based upon the cost and scalability requirements of the application.
The other important factors that have to be considered when selecting the processors are the following. Since, they are known to most people, I am not explaining each of them.
o Processor Cores
o L2 Cache
o Hyper threading

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