Connection Pool
A bounded resource pool that reuses database or remote-service connections instead of repeatedly paying connection-establishment cost.
Why Pool Connections?
Opening a database connection can involve authentication, network setup and server-side resource allocation. A connection pool returns a used connection to a managed pool rather than physically closing and recreating it for every request.
Pool Size Is Not Database Capacity
Increasing pool size does not create more CPU, I/O or lock capacity in the database. An oversized pool can increase contention by allowing too much concurrent SQL work.
An undersized pool instead increases application-side connection wait time.
What to Measure
Active/idle connections, waiting work, acquisition latency, transaction duration and timeout behavior should be observed together.
If pool capacity and application concurrency are unconstrained independently, queues can grow under load.
Applied Context
My Advanced Connection Pool Design with HikariCP article examines this boundary in a Java/Oracle context.