Spring Boot Hikari Default Pool Size

The default pool size of HikariCP is 10.

You can check it from HikariCP class com.zaxxer.hikari.HikariConfig

Other default values are

private static final long CONNECTION_TIMEOUT = SECONDS.toMillis(30);
private static final long VALIDATION_TIMEOUT = SECONDS.toMillis(5);
private static final long SOFT_TIMEOUT_FLOOR = Long.getLong("com.zaxxer.hikari.timeoutMs.floor", 250L);
private static final long IDLE_TIMEOUT = MINUTES.toMillis(10);
private static final long MAX_LIFETIME = MINUTES.toMillis(30);
private static final long DEFAULT_KEEPALIVE_TIME = 0L;
private static final int DEFAULT_POOL_SIZE = 10;

To change default pool size, configure maximum-pool-size in application.properties file as below.