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Date: Wed, 21 Sep 2011 15:49:09 +0000 (UTC)
From: "Stephen Allen (JIRA)" <jira@apache.org>
To: jena-dev@incubator.apache.org
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Subject: [jira] [Updated] (JENA-120) Query objects with aggregators cannot
 be reused
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     [ https://issues.apache.org/jira/browse/JENA-120?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stephen Allen updated JENA-120:
-------------------------------

    Attachment: JENA-120-r1173729.patch

Ah, the BindingKeys are not considered equal because they can mutate!  This is probably not what we want (and in particular it's a bad idea to mutate keys in a hashtable).

Since BindingKey only maintains a reference to the binding, when the aggregation is added to the binding as an additional variable/value pair (QueryIterGroup.java line 141) it changes the .equals() and .hashCode() values.

I've attached a patch that stores a copy of the binding in BindingKey rather than a reference.  This causes testReuseQueryObject2 to fail without the initial patch and pass when it is applied.


> Query objects with aggregators cannot be reused
> -----------------------------------------------
>
>                 Key: JENA-120
>                 URL: https://issues.apache.org/jira/browse/JENA-120
>             Project: Jena
>          Issue Type: Bug
>          Components: ARQ
>            Reporter: Stephen Allen
>            Assignee: Andy Seaborne
>            Priority: Minor
>         Attachments: JENA-120-r1173178.patch, JENA-120-r1173729.patch
>
>
> Query objects that contain aggregators (Group By) cannot be reused by different threads because the internal state is mutable.  Even reusing a query object in the same thread has problems, because it creates a new Aggregator object each time you execute the query.  Users may want to reuse Query objects to save having to reparse the query string.
> I believe the solution is to copy the aggregators when compiling the query.  I've attached a patch that does that in the AlgebraGenerator.compileModifiers() method.
> See the thread at [1] for more discussion.
> [1] http://mail-archives.apache.org/mod_mbox/incubator-jena-users/201109.mbox/%3CB60ACA3A-DB31-4FEC-A72E-D81A5C2AB41A@knublauch.com%3E

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