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https://issues.apache.org/jira/browse/CAY-1225?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrey Razumovsky closed CAY-1225.
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Resolution: Fixed
Fix Version/s: 3.0 beta 1
Assignee: Andrey Razumovsky
> Controlling JDBC Driver setting "fetchSize" in a SelectQuery
> ------------------------------------------------------------
>
> Key: CAY-1225
> URL: https://issues.apache.org/jira/browse/CAY-1225
> Project: Cayenne
> Issue Type: Improvement
> Components: Cayenne Core Library
> Affects Versions: 2.0 branch
> Reporter: Stephane Claret
> Assignee: Andrey Razumovsky
> Priority: Critical
> Fix For: 3.0 beta 1
>
> Attachments: SelectAction.java, SelectQuery.java
>
>
> ResultIterator is a nice API for dealing with large SELECT queries,
> unfortunately some JDBC drivers that don't automatically use server-side
> cursors (eg PostgreSQL JDBC driver) wont'give access to the ResultSet (at
> JDBC level) until the whole query has finished executing and all rows have
> been returned.
> It basically mean that if you execute a SelectQuery returning 1'500'000 rows,
> there's a high chance of getting a OutOfMemoryException in the JDBC driver
> code (Statement.Excecute), before Cayenne even gets a chance to call the
> ResultSet.Next().
>
> It makes the ResultIterator API much less efficient than it could be because :
> -Even if rows are processed one by one, they need to be stored in local
> memory, causing heap size issues.
> -In some scenarios, user code could start working with the resulting rows
> immediately as they become available, while the select query is still being
> executed by the database engine.
> To solve this problem, there should be a way to have the SelectQuery object
> calling Statement.setFetchSize() before it executes.
> A SelectQuery.setFetchSize( int ) method would be perfect because it's often
> needed to configure this setting on a per-query basis.
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