This topic describes the configuration parameters of a connection pool, including the ZDAL, Druid, DBCP, C3P0, and JDBC parameters.
Data source parameters
Parameter type | Description | ZDAL parameter | Druid parameter | DBCP parameter | C3P0 parameter |
Number of initial connections | The number of connections established during initialization of the connection pool. | prefill=true, initialized to minConn | initialSize(0) | initialSize(0) | initialPoolSize(3) |
Minimum number of connections | The minimum number of available connections retained for the connection pool. | minConn(0) | minIdle(0) | minIdle(0) | minPoolSize(3) |
Maximum number of connections | The maximum number of available connections. If the number of connections in the connection pool exceeds this number, an exception is returned, indicating that the connection pool is full. | maxConn(10) | maxActive(8) | maxActive(8) | maxActive(8) |
Connection idle timeout period | The period of connection idle time that the connection pool waits for before it disconnects the connection. MySQL disconnects a connection that has been idle for 8 hours by default. A connection becomes a dirty one during the active/standby switchover. Without this mechanism, a request may fail. For ApsaraDB for OceanBase, the default SLB timeout period is 15 minutes. You can set it to 12 minutes. | idleTimeoutMinutes(30min) | minEvictableIdleTimeMillis(30min) | This parameter takes effect only when timeBetweenEvictionRunsMillis(-1) > 0 is set. This parameter specifies the asynchronous check cycle. | maxIdleTime (0 indicates no timeout.) |
Timeout period for obtaining a connection from the connection pool | If the value is too large, the application response will be very slow when the connection pool is full. | blockingTimeoutMillis(500ms) | maxWait (-1 indicates no timeout.) | maxWaitMillis (-1 indicates no timeout.) | checkoutTimeout (0 indicates no timeout.) |
Timeout period before destroying a connection | If a connection is not returned to the connection pool after this period, the connection is directly destroyed. This mechanism prevents connection leakage but restricts the duration in which a connection can be used by a transaction. | None | removeAbandonedTimeoutMillis(300s) | removeAbandonedTimeout(300s) | None |
JDBC parameters
The following JDBC parameters are important and must be configured. You can specify these parameters in the connection properties of the connection pool or the JDBC URL. The following table describes the parameters.
Parameter | Description | Default value |
socketTimeout | The network timeout period for a read request. The default value is 0, which means that the default timeout period of the operating system is used. | 5000ms |
connectTimeout | The timeout period for establishing a connection. The default value is 0, which indicates that the default timeout period of the operating system is used. | 500ms |
Recommendations on connection pool settings
You can retain a minimum of two connections for the console and adjust the configuration based on the business concurrency and transaction time.
We recommend that you set the idle connection timeout period to 30 minutes.
By default, MySQL disconnects a connection that has been idle for 8 hours, which cannot be sensed by the client. This results in dirty connections. The connection pool can check whether a connection is alive through mechanisms such as heartbeats or testOnBorrow. When the connection has been idle for this period, the connection is disconnected.