How to Set Up a Validation Query for DBCP with Different Databases?

What value should I use for the validationQuery property in DBCP when connecting to different databases such as DB2, Oracle, and HSQLDB?

validationQuery="SELECT 1 FROM DUAL" for Oracle
validationQuery="SELECT 1 FROM SYSIBM.SYSDUMMY1" for DB2
validationQuery="SELECT 1" for HSQLDB

When configuring the Apache DBCP (Database Connection Pooling) library, the validationQuery property is essential for ensuring that connections to various databases are valid before they are borrowed from the pool or returned to it. Given the diversity of SQL dialects among different databases, you may need to tailor the validation query accordingly.

// Example configuration settings in your DBCP pool setup
connectionPool.setTestOnBorrow(true);
connectionPool.setTestOnReturn(true);
connectionPool.setValidationQuery("SELECT 1 FROM DUAL"); // For Oracle
// connectionPool.setValidationQuery("SELECT 1 FROM SYSIBM.SYSDUMMY1"); // For DB2
// connectionPool.setValidationQuery("SELECT 1"); // For HSQLDB

Causes

• Each database management system (DBMS) has its own SQL syntax and methods for performing simple queries.
• Not having a valid validationQuery can lead to connection issues at runtime.

Solutions

• Use database-specific SELECT statements that can ensure a valid connection. Below are suitable queries for the specified databases:
• For Oracle: SET validationQuery to `SELECT 1 FROM DUAL` - This is a simple query that returns one result from the dual table, which is always present in Oracle databases.
• For DB2: SET validationQuery to `SELECT 1 FROM SYSIBM.SYSDUMMY1` - Similar to Oracle's dual table, this select from the dummy table is always guaranteed to return a result.
• For HSQLDB: Simply use `SELECT 1` - HSQLDB accepts this straightforward query which returns 1.

Mistake: Using a validationQuery that does not return a row or uses incorrect SQL syntax for the target DBMS.

Solution: Always test the validationQuery in your SQL client first before using it in the DBCP configuration.

Mistake: Not setting `testOnBorrow` and `testOnReturn` properties.

Solution: Ensure these properties are set to true to enforce the validation of connections at the appropriate stages.