What is the difference between corePoolSize and maxPoolSize in the Spring ThreadPoolTaskExecutor

Question

I have to send out massEmails to all users of a website. I want to use a thread pool for each email that is sent out. Currently I have set the values to :

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Answer 1

In addition to what @skaffman pointed out from official docs, following also makes it more clear how these sizes are utilized:

Any BlockingQueue may be used to transfer and hold submitted tasks. The use of this queue interacts with pool sizing:

• If fewer than corePoolSize threads are running, the Executor always prefers adding a new thread rather than queuing.
• If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread.
• If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.