What is ideal size of Fixed Thread pool?

Question

Fixed Thread pool has been used to limit the number of threads in java application by passing an integer variable to the executors method like below

Executors.newFixedThreadPool(10);

Suppose we are designing any application and we are using fixed thread pool then how can we take up a decision for an ideal fixed thread pool size or on what basis we should decide the fixed thread pool size ?

Answer 1

First of all,

1.) Are you creating a FixedThreadPool for the whole application or for specific task in your application?

2.) The server on which your application is deployed, supports how many CPU's, per CPU how many threads?

3.) There might be a case, where you are allocating fewer threads than the server has, or might allocate more, and your tasks doe not require that many. It is more or less a waste of resources.

Thread pool sizes should rarely be hard-coded; instead pool sizes should be provided by a configuration mechanism or computed dynamically by consulting Runtime.availableProcessors.

For more, Java Concurrency in Practice has a detailed chapter on thread pools.