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Are MySQL operations multithreaded?
Specifically, on running a select, does the select (or join) algorithm spawn multiple threads to run together? Would being multi-threaded prevent being able to support a lot of concurrent users?
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One feature of some operating systems is the ability to run several threads of execution within a single process. This allows an application to handle asynchronous events, and makes it easier to create event-driven applications without resorting to polling schemes.
SQL servers are designed to handle multiple connections but every entry in to the transaction log has to be handled sequentially. In short, many people can on multiple threads be connected to the server, but only 1 transaction can occur at any given point in time.
The maximum number of threads per group is 4096 (or 4095 on some systems where one thread is used internally). The thread pool separates connections and threads, so there is no fixed relationship between connections and the threads that execute statements received from those connections.
Multithreading is a Java feature that allows concurrent execution of two or more parts of a program for maximum utilization of CPU. Each part of such program is called a thread. So, threads are light-weight processes within a process. Threads can be created by using two mechanisms : Extending the Thread class.
Several background threads run in a MySQL server. Also, each database connection is served by a single thread. Parallel queries (selects using multiple threads) are not implemented in MySQL.
MySQL as is can support "a lot of concurrent users". For example Facebook started successfully with MySQL.
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