High request loads


Can somebody explain how sites like, YouTube can have 1000 users all streaming the same vidio clip at once?  I thought there would be some sort of limit much lower. HHow do they achieve this?  I am sure they spread the load over numerous servers, so is it just hat they have thousands hundreds of servers hosting a particular clip?

Similarly, web sites, e.g banking websites, what if 1000's of people log in on moonday morning to see if their interst has been paid.  I guess Ive experienced not being able to log in during busy times, but how do they make it available to soo many people?
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keithdmitchellConnect With a Mentor Commented:

The difference between websites like youtube is that they share the load among many clustered servers and use load balancing.  You also have to keep in mind that for every web server they have that streams media that there is also a sql server in the backgroup and  likely a different server to handle the thousands of requests for converting the multiple video types to flash files (since youtube does not stream avi's, mpegs, wmvs, mov's or xvid files).

So for your answer, it is load balancing. There is a certain number of servers that are setup and are mirrored (database's) and load balanced. Meaning if you access the site and the server knows it can't handle the load , it will move your session to a server that can handle the load. The more servers that are in the configuration, the more complex that network becomes as it has to evenly distribute the traffic and all the data on the servers has to be consistant and constantly updated across the servers.

You can look at this more indepth by viewing this wiki link - http://en.wikipedia.org/wiki/Load_balancing_(computing)

This link is for a book on server load balancing, by O'Reilly and is a good read - http://books.google.com/books?id=3qKogfm3CygC&dq=load+balancing&printsec=frontcover&source=bl&ots=v-pMurt5m5&sig=OD6Wzfaq2GAkXlevZNpCNWLgNZE&hl=en&ei=iH4ESsXBMs-wmAfrnNzcBA&sa=X&oi=book_result&ct=result&resnum=3#PPR12,M1

Another good example is Cloud Computing. Cloud computing for lack of a better term is load balancing on a larger scale.

Hope that helps you.

Keith D Mitchell
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