Multiple servers for client server application

I am writing a client server application. I suspect I'll have 250,000 clients at peek times.

What types of socket bottle necks should I expect?

I've been told to make it scalable so we can add more servers as the need arises. How many clients should I expect to connect per server?

I've started with a single server. The client is accessing data contained in a data structure, held in memory. If I have multiple servers, what is the best and fastest way to share the data between servers on my LAN? Can I share a memory space? Should I use a database instead of memory, and share the database?

Any advice or ideas would be great.

Thanks,
Lee

Database would be good. If you're gonna use MySQL (which i suggest you should, it is by far the best [and free]) then you create a HEAP Table. HEAP tables are stored in the memory (RAM). Then to save this information, simply write it to a MyISAM table (default MySQL table, stored on HD).

Hope this helps. Keep the questions coming.

If you're going to have 250,000 clients downloading data at the same time, there's something else to consider:

Even assuming a lightning fast server farm and database, if you have a 1Mb connection to the internet, you can get a speed of approximately 1 byte every 2 seconds to each client. That's a download speed per client of about 30bps. Not too impressive. Even if you run a 10Mb connection directly to your backbone (pretty expensive), that's 300 bps. Has anyone included that into the calculations? (Downloading would take about 3 seconds/K, or 30 seconds/M, not something people will find comfortable these days, and certainly not in the future.)

Depends on what the clients are to be downloading. If it is just text then add a few more servers in a chain and it'll be fine (note, the servers must have an individual xDSL)

The data volume is similar to that of a chart room with messagess passed back and forth. (10 users per room max)

This is actually a poker client server application.