How much memory should a caching system use on Windows?

Rather than create your own caching algorithms why don't you write the data to a file with the FILE_ATTRIBUTE_TEMPORARY attribute and make use of the client machine's own cache.

Although this approach appears to imply that you use a file, if there is memory available in the system then the file will never leave the cache and will remain in memory the whole time.

Some advantages:

• You don't need to write any code.
• The system cache takes account of all the other processes running. It would not be practical for you to take that on yourself.
• On 64 bit Windows the system can use all the memory available to it for the cache. In a 32 bit Delphi process you are limited to the 32 bit address space.
• Even if your cache is full and your files to get flushed to disk, local disk access is much faster than querying the database and then transmitting the files over the network.

It depends on what other software runs on the server. I would make it possible to configure it manually at first. Develop a system that can use a specific amount of memory. If you can, build it so that you can change that value while it is running.

If you got those possibilities, you can try some tweaking to see what works best. I don't know any golden rules, but I'd figure you should be able to set a percentage of total memory or total available memory with a specific minimum amount of memory to be free for the system at all times. If you save a miminum of say 500 MB for the server OS, you can use the rest, or 90% of the rest for your cache. But those numbers depend on the version of the OS and the other applications running on the server.

I think it's best to make the numbers configurable from the outside and create a management tool that lets you set the values manually first. Then, if you found out what works best, you can deduct formulas to calculate those values, and integrate them in your management tool. This tool should not be an integral part of the cache program itself (which will probably be a service without GUI anyway).

Questions:

1. One image can be requested by multiple clients? Or, one image can be requested by multiple times in a short interval?

2. How short is the interval?

3. The speed of the network is really high? Higher than the speed of the hard drive?? If you have a normal network, then the harddrive will be able to read the files from disk and deliver them over network in real time. Especially that Windows is already doing some good caching so the most recent files are already in cache.

4. The main purpose of the computer that is running the server app is to run the server? Or is just a normal computer used also for other tasks? In other words is it a dedicated server or a normal workstation/desktop?

but should I ask the user how much memory he is willing to allocate to my application ?

I would definitively go there!!!If the user thinks that the server application is not a important application it will probably give it low priority (low cache). Else, it it thinks it is the most important running app, it will allow the app to allocate all RAM it needs in detriment of other less important applications.

Just deliver the application with that setting set by default to a acceptable value (which will be something like x% of the total amount of RAM). I will use like 70% of total RAM if the main purpose of the computer to hold this server application and about 40-50% if its purpose is 'general use' computer.