Question

I use DBCP pool and I want use testOnBorrow and testOnReturn to test if connection is still valid.
Unfortunately I have to set property validationQuery to make it work.

Question: What value should be in validationQuery?

I know, that: validationQuery must be an SQL SELECT statement, that returns at least one row.

Problem is that we use various databases (DB2, Oracle, hsqldb).

Answer 1

There is not only one validationQuery for all databases. On each database you have to use different validationQuery.

After few hours of googling and testing I have collected this table:

Database validationQuery notes

• hsqldb – select 1 from INFORMATION_SCHEMA.SYSTEM_USERS
• Oracle – select 1 from dual
• DB2 – select 1 from sysibm.sysdummy1
• mysql – /* ping */ select 1
• microsoft SQL Server – select 1 (tested on SQL-Server 9.0, 10.5 [2008])
• postgresql – select 1
• ingres – select 1
• derby – values 1
• H2 – select 1
• Firebird – select 1 from rdb$database
• MariaDb – select 1
• Informix – select 1 from systables
• Hive – select 1
• Impala – select 1

I wrote about it on my blog – validation query for various databases.

In advance there is an example of class, which return validationQuery according to JDBC driver.

Or does anybody have better solution?