Database and Ajax

Database and Ajax
Younger brother recently want to try to write a network chat room, encountered a chat record storage problems. Kazakhstan exists database Well, my classmates let me exist in the file and then the way to read Ajax, he said that the existence of the database will have a large impact on performance, so want to ask, is directly present in the file or the existence of the database, or you prawns have what with a good way to teach Oh, younger brother greatly appreciated

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It's good in XML.
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Open the database to hold the data directory, you will see a file. So, the database is also the data stored in the file
Since it's all written and read, how much does it affect performance?


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Personal feel that the file is less than the database performance (the chat room estimate can not be seen, the amount of data is a big feeling)
Just the content of the chat room is a temporary session, so feel no need to save the database!
You can do it with XML!

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