Enhancement

Currently, the default thread number of a background thread pool is 16. And there are two background thread pools for different purposes, so the total number of background threads is 32.

This is not suitable for all scenarios, especially the cloud environment since the number of CPUs per instance is small (usually 16 vCPU per instance).

I think setting the default thread number of a background thread pool to a quarter of the number of CPUs is enough.

• Configuration's name profiles.default.background_pool_size .