How does HikariCP handle incomplete JDBC transactions?

Question

Yesterday I came across HikariCP and spent the whole night studying it. I'm really impressed with the amount of detail and effort put into fine tuning its implementation and design. Straight to the point, I could not determine how it actually deals with connections that are checked back into the pool with their autoCommit set to false, while neither commit() nor rollback() is issued on them, for example, due to an exception. This potentially can be the source of many serious transactional problems for the next requester that expects a fresh connection but unfortunately receives this connection with its dangling transaction state.

While C3P0 and Tomcat's JDBC pool have some of these so called Knobs for this very purpose (through configuration or interception), I could not find anything in HikariCP's documentation or support group. Please correct me if I'm wrong, but writing a simple unit test showed me that the pool does nothing about this.

I need to know if this observation is actually correct and I'm not missing anything about it. Also, if there is any plan for addressing this in HikariCP since it is critical for me.

Thanks.

Answer 1

I am one of the authors of HikariCP. HikariCP does not automatically execute either commit or rollback if auto commit is turned off. It is generally expected that an application that is turning off auto commit explicitly is prepared to properly handle these (recommended in a finally block) -- as in this example from the official JDBC documentation.

We are willing to add automatic "rollback" behavior to HikariCP (but not automatic "commit") if a connection is returned to the pool with auto commit set to false. Please open a feature request if you wish this behavior.

UPDATE: HikariCP 1.2.2 and above perform an automatic "rollback" for closed connections with auto-commit set to 'false'. Additionally, it will reset transaction isolation level to the configured default, and as noted in comments below will of course close open Statements, etc.

UPDATE: HikariCP 2.3.x and above now additionally track transaction state when auto-commit is set to false, and will bypass the automatic rollback operation if the transaction state is clean.