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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