[Hibernate-issues] [Hibernate-JIRA] Commented: (HB-1246) HILO id can cause deadlock

[Bruce A. (JIRA) <no...@at...>]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HB-1246?page=comments#action_22656 ] 

Bruce Atherton commented on HB-1246:
------------------------------------

This one has bit us badly during load testing. We tried the "don't use a connection pool which limits the number of open connections", but that just led to hitting the connection limit on the database. We've had to abandon hilo and turn to native, which is causing us other kinds of grief.

There is an easy solution for this bug, though. Just allow the user the option to define a separate connection pool for the hilo generator. Anyone who runs into this deadlock issue can then configure the generator to draw from a different data source.

Can I request that this issue be reopened with that solution in mind?


> HILO id can cause deadlock
> --------------------------
>
>          Key: HB-1246
>          URL: http://opensource.atlassian.com/projects/hibernate/browse/HB-1246
>      Project: Hibernate2
>         Type: Bug

>   Components: core
>     Versions: 2.1.6
>  Environment: HILO id generation with a fixed connection limit
>     Reporter: Edward Costello

>
>
> The HILO generator attempts to obtain a connection to the database in addition to the one being used by the current session. If no connections are available and all sessions are attempting an operation that requires ID generation, this will result in deadlock (at least until the connection pool times out the request and the exception kills one of the requesting sessions).
> The simple case to observe this effect is:
> 1) Set up the connection pool to provide only a single connection.
> 2) Attempt to save an object using HILO id generation.
> This issue can also occur when there is more than one connection available.
> E.G if there are 5 connections, 5 threads open a session, all 5 attempt to save. All 5 threads will be blocked while they each try and obtain a connection for the id generator.
> --- Code to Reproduce ---
> Configuration cfg = new Configuration();
> cfg.configure(......); // Configured Pool must only allow 1 connection
> SessionFactory sf = cfg.buildSessionFactory();
> Session s = sf.openSession();
> Transaction tx = s.beginTransaction();
> s.save(new PersistedObject());
> tx.commit();
> ---- Suggested Resolution ---
> The best solution we have come up with is to allow for the configuration of a second smaller connection pool that is used exclusively for HILO (and any other generation types requiring a separate connection).
> This pool would be optional and if not specified the main pool would be used (i.e. the current behaviour).

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