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Date: Thu, 19 Jun 2008 16:19:45 -0700 (PDT)
From: "Kathey Marsden (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Created: (DERBY-3732) SQL Length function materializes lob
 into memory
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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: 10.4.1.3, 10.3.3.0, 10.5.0.0
            Reporter: Kathey Marsden
            Priority: Minor
         Attachments: LengthLargeLob.zip

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
[C:/kmarsden/repro/10153] ls


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