I have the below doubts on the Hikari or any database pooling concept.
when does the connection pool gets created? Suppose if I have mentioned spring.datasource.hikari.maximum-pool-size=50 Will it create 50 database instances?
As by default, spring scopes on classes in single ton, how 50 instances are created?
Thanks in advance!
CodePudding user response：
Connection pooling helps reducing in creating database connections everytime a database call is encountered.
Pool would be nothing but set of connections (ideally active) (Like we have thread pool ), when requested will return one active connection ( or create one for first database request) , instance would be a misfit word here !
To answer first part of your question, it is initialized during application startup when that spring.datasource.hikari... property is encountered.
Below link explains this concept well
https://coderstea.in/post/best-practices/jdbc-connection-pooling-explained-with-hikaricp/
CodePudding user response：
1:
A connection pool will be created when the first connection is creating. For example when the first SQL is executed. {@link com.zaxxer.hikari.HikariDataSource#getConnection()}.
This is my case and maybe it's different according the ORM you are using.
Connection instances will be created by the connection pool. {@link com.zaxxer.hikari.pool.HikariPool#poolEntryCreator} {@link com.zaxxer.hikari.pool.HikariPool#postFillPoolEntryCreator}
"spring.datasource.hikari.maximum-pool-size=50" means that the connection pool would not create connection instance more than 50. So it is the limit for connection instance count in connection pool.
2:
Spring Bean is singleton by default. But connection instances in the conneciton pool are not "spring bean" and they are created from "new PoolEntry". {@link com.zaxxer.hikari.pool.HikariPool#createPoolEntry}