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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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Stephane Claret updated CAY-1225:
---------------------------------
Attachment: SelectAction.java
SelectQuery.java
Modified files:
Original come from v3 M6 generic-unpulished version.
-People who can't wait for this feature to be publicly available can use this
patch. Modified sections are marked with comment "quick fix".
-I added cursorFetchSize property in SelectQuery (nullable Integer). If set, it
is used to modify the preparedStatement in SelectAction.performAction otherwise
it has no effect, there should be no risk to break existing code.
> 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
> Priority: Critical
> 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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