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Date: Fri, 20 Jun 2008 11:15:45 -0700 (PDT)
From: "Kathey Marsden (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-3732) SQL Length function materializes lob
 into memory
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     [ https://issues.apache.org/jira/browse/DERBY-3732?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kathey Marsden updated DERBY-3732:
----------------------------------

    Attachment: LengthThruBlob.java

One possible workaround is just to select the BLOB and call Blob.length().  worst case this call will  go through the entire stream without materializing.  When inserting the Blob, it is better to use the setBinaryStream call that takes length so that the length is stored in the stream and the call to Blob.length() willl be a lot faster.  See attached program LengthThruBlob. It needs Astream.java from the original repro zip file.


> SQL Length function materializes lob into memory
> ------------------------------------------------
>
>                 Key: DERBY-3732
>                 URL: https://issues.apache.org/jira/browse/DERBY-3732
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.3.3.0, 10.4.1.3, 10.5.0.0
>            Reporter: Kathey Marsden
>            Priority: Minor
>         Attachments: LengthLargeLob.zip, LengthThruBlob.java
>
>
> Currently the SQL length function materializes the entire lob into memory. In SQLBinary.getLength() we have 
> public final int	getLength() throws StandardException
> 	{
> 		if (stream != null) {
> 			if (streamValueLength != -1)
> 				return streamValueLength;
> 		}
> 		return (getBytes() == null) ? 0 : getBytes().length;
> 	}
> Which actually is doubly bad because we call getBytes twice and materialize it twice.
> It would be good to read the length from the stream if available and otherwise stream the value to get the length, rather than materializing it into memory.
> To reproduce, run the attached repro.
> java -Xmx16M  LengthLargeLob
> It gives an out of memory exception
> Caused by: java.lang.OutOfMemoryError: Java heap space
>         at org.apache.derby.iapi.types.SQLBinary.readFromStream(SQLBinary.java:415)
>         at org.apache.derby.iapi.types.SQLBinary.readExternal(SQLBinary.java:318)
>         at org.apache.derby.iapi.types.SQLBinary.getValue(SQLBinary.java:220)
>         at org.apache.derby.iapi.types.SQLBinary.getBytes(SQLBinary.java:210)
>         at org.apache.derby.iapi.types.SQLBinary.getLength(SQLBinary.java:250)
>         at org.apache.derby.impl.sql.execute.BaseActivation.getDB2Length(BaseActivation.java:1684)
>         at org.apache.derby.exe.acf81e0010x011axa317x5db8x0000003d9dc81.e1(Unknown Source)
>         at org.apache.derby.impl.services.reflect.DirectCall.invoke(ReflectGeneratedClass.java:141)
>         at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.doProjection(ProjectRestrictResultSet.java:497)
>         at org.apache.derby.impl.sql.execute.ProjectRestrictResultSet.getNextRowCore(ProjectRestrictResultSet.java:291)
>         at org.apache.derby.impl.sql.execute.BasicNoPutResultSetImpl.getNextRow(BasicNoPutResultSetImpl.java:460)
>         at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(EmbedResultSet.java:423)
>         ... 2 more
> [
>  

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