[hibernate-issues] [Hibernate-JIRA] Commented: (HSEARCH-598) MassIndexer freezes when pool size is too low

[Sanne Grinovero (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-598?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=39946#action_39946 ] 

Sanne Grinovero commented on HSEARCH-598:
-----------------------------------------

Another case: https://forum.hibernate.org/viewtopic.php?f=9&t=1009524

I don't think we can detect this, but I could re-arrange the order of thread start to start first the minimum number of threads needed to keep it alive, and then gradually attempt to increase them - optimistically. If after that some threads fail to make progress, we won't know that nor be able to warn. It would work just fine, just suboptimal for performance; depending on point of view, it might be considered optimal: if we can't have more connections, that's the best it can do.

> MassIndexer freezes when pool size is too low
> ---------------------------------------------
>
>                 Key: HSEARCH-598
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-598
>             Project: Hibernate Search
>          Issue Type: Bug
>          Components: documentation, massindexer
>    Affects Versions: 3.2.1
>         Environment: Hibernate Core 3.5.4, PostgreSQL 8.4.4
>            Reporter: I D
>            Assignee: Sanne Grinovero
>             Fix For: 3.2.2, 3.4.0
>
>
> In our application we use db connection pooling at the servlet container level - Jetty instantiates a com.mchange.v2.c3p0.ComboPooledDataSource. We've disabled Hibernate's connection pooling to avoid multiple connection pools.
> Soon after starting to use MassIndexer we noticed that it SOMETIMES freezes during operation - startAndWait() just hangs indefinitely. After some experimentation, we realized that during this freeze the connection pool is maxed out and all the 15 connections (c3p0's default value for maxPoolSize is 15) are active.
> We therefore experimented with various values for maxPoolSize and found that 10 or less always seems to cause freezes, whereas 20 or more seems to work fine consistently. In between is a grey area, where the freeze occurs inconsistently (this grey area may of course extend to maxPoolSize<=10 and/or maxPoolSize>=20, since our tests only provide a partial statistical sample).
> If this is expected behavior, the minimal pool size / number of required connections should be well documented.

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