I've an Spring Boot REST async application, wanna adjust:
Browsing documentations and sites found possibilities:
corePoolSize value=... VS server.tomcat.max-threads = ... - What is the difference?
spring.datasource.hikari.maximum-pool-size= ... VS spring.datasource.tomcat.max... = ... - What is the difference?
Assuming you are using Spring Boot 2.1 and haven't changed the defaults (using Tomcat as the embedded container and Hikari as the connection pool).
To modify the number of threads (tomcat by default already uses 200 so why would you need to change it!) use the properties in the server.tomcat namespace (those are specific for Tomcat!. So use server.tomcat.max-threads to control the number of request handling.
To limit the number of concurrent HTTP connections use the server.tomcat.max-connections (default value 10000). This is basically the processing queue which the request handling threads use to pick/steal work from.
For controlling the number of threads used by the default created TaskExecutor in Spring Boot 2.1 use the properties in the spring.task.execution namespace. So use spring.task.execution.pool.max-threads to set the maximum number of threads to use for @Async. The spring.task.execution.pool.core-size controls the core (minimum) pool-size. Increasing the max-threads property without limiting the queue size through spring.task.execution.pool.queue-capacity has no effect. The default queue size is unbounded and everything will not result in growing the number of threads beyond the core-size.
Finally to specify the connections for your connection pool (the default for Hikari is 10!). Use the spring.datasource namespace properties and specifically the one for your connection pool (default is Hikari so the ones in spring.datasource.hikari, the spring.datasource.tomcat are for the Tomcat JDBC connection pool used as default on Spring Boot before 2.0). So set the spring.datasource.hikari.maximum-pool-size to manage to max number of threads.
They don't have anything to do with each other and should be confused with each other as well (imho this is already clear in the reference guide that each serves a different purpose). See Appendix A of the Spring Boot Reference Guide for a list of common properties.
