I'm confused about concurrent MySQL connections

Question

So, I read a book in Mysql and it says that there's a limit on how many concurrent users that can access a database.

Does that mean that If I have 20k users browsing in my web application concurrently, my web application will fail to load the data in my database? Because my web application is accessing the database every time my website loads.

Answer 1

20k users loading a page at the exact same time ? That's quite a lot -- and your webserver will probably not accept that many concurrent requests itself (For example, Apache generally accepts only between 200 and 400 parallel requests).

The connection limit is the maximum number of users that can be connecter to your database at the exact same time -- if each page needs 100 ms to be generated, one user will only be connected for less than 100 ms.
And if you connect to your database just when you need to do your first SQL query, and disconnect immediately after your last SQL query, this can reduce the time during which your Webserver is connected to the DB.

If you have users reading content from your website, you can consider they will :

• Load a page (maybe 100 ms on your server)
• Do nothing but read for a couple of minutes (which takes absolutly no resource on your server)

As a sidenote : quite a long time before getting 20k concurrent connections (which means about 20,000 connections per second or so !), you'll probably have to deal with several scaling-relating problems...

Answer 2

If you get a Too many connections error when you try to connect to the mysqld server, this means that all available connections are in use by other clients.

The number of connections permitted is controlled by the max_connections system variable. Its default value is 100. If you need to support more connections, you should set a larger value for this variable.

You should ask your system administrators to do these changes only when necessary.