Website Hosting Sever, some Pitfalls you need to avoid part 3

Posted by arlene

Hosting Sever System Lack of Scalability

Scalability is the ability to increase the amount of computing resources available to run an application with minimum impact on the application software and minimum administrative effort. The measure of scalability is somewhat subjective, but to be scalable, the system must have at least the following characteristics:

Adding new servers with computer platforms of the same type as already in use should have no effect on application programs; that is, it must require no program changes, no recompiling of programs, and no relinking of programs.

The underlying support software should require no changes or reinstallation on the existing platforms.

• Administrative changes to existing system definitions should be minimal.
• Adding a server platform that can run the same executables as already exist should require no more than the following effort:

• Installing and setting up the new platform.
• Redistributing the data.
• Copying application programs to the new system.
• Adding the definition of the new system to the administrative control files of the existing system.
• Defining routing of service requests to the new system.

If the new server is a platform that is not capable of running existing executables, the only additional step required should be recompiling the application programs on the new platform.

Some client/server application development tools claim that there is no need to recompile the application to move to a different machine type. These systems work functionally, but they must run interpretively (every statement is parsed and compiled, then executed one by one as the application is run), causing poor performance.

Some enterprises have installed a system and made it work very well, but then found that they could not expand capacity without major rework of the application systems. This problem is sometimes compounded by a failure of the development system to move easily to new, more efficient platforms without major efforts to reinstall all existing support software.

Hosting Sever System Poor Performance

Modern enterprises depend on computers for mission critical information-intensive operations. Computer systems users must have accurate information quickly if they are to be productive. Yet performance where it counts—at the end user—is perhaps the least measured factor in managing costs. If the system is sluggish and causes a few seconds of extra wait on each use, the loss in productivity can be staggering. For example, if 100 people are using the system and they must wait an extra few seconds on each transaction during the day (this wait is a time of complete idleness), the total loss can reach ten minutes each day for each person. The total loss is over 16 person-hours lost each day because of slow computer response. This calculation is based on 100 transactions per day, with a loss of six seconds with each transaction. The importance of performance cannot be overstated.

Poor performance may be one of the most vexing problems complained about by those who have installed client/server systems. Among the many reasons why performance does not come up to expectations are these common ones:

• The support software, such as an object-oriented development tool, put too much data on the network, causing slow network response.
• The support software starts too many processes in the server, causing the server to spend too many central processing unit (CPU) cycles switching from process to process.
• All processing is done in the work station, causing poor performance unless more expensive work stations are installed.
• The database is not properly defined to maximize performance.

Some highly publicized client/server development tools start a process in the server for every user on the system. Most operating systems, UNIX particularly, use CPU cycles to switch from process to process. The number of cycles used rises exponentially with the number of processes that are available to run. When a few processes are involved, adding one more makes little difference, but if there are hundreds of users and each has a dedicated process on the server, the server will often become busy with simply process switching. Adding computer power helps but does not correct the underlying problem. Client/server systems should have a way to reuse processes started in the server. Further, there should be an administrative feature that allows control of the number of processes started.

When all the processing is done in the work station, using the server only as a database server, it requires more computing power in the work station. Some companies have planned their client/server systems using smaller, lower-priced work stations and have suffered slow processing times. The work load must be balanced between the work stations and the servers to achieve the desired price-performance ratios.

If the database is not distributed among the disk storage devices properly, a large amount of head movement will be required for each transaction. When this occurs, performance can suffer heavily. The chosen database should allow easy tuning of data distribution over the available disk, and the combination of the client/server software and the database software should allow changing the data distribution without great effort, with easy placement of data.

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