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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3732) SQL Length function materializes lob into memory
Date Fri, 27 Jun 2008 09:23:45 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3732?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12608707#action_12608707
] 

Kristian Waagan commented on DERBY-3732:
----------------------------------------

I had a look at 'derby-3732_skip2_diff.txt' and have the following comments:
 a) Instead of using your own stream (Astream), can you use one of the existing streams for
testing?
    Using a stream that only returns the same value over and over doesn't detect off-by-one
errors or similar (which I introduced myself and had to debug as part of DERBY-3735). The
simplest one we have is LoopingAlphabetStream for lowercase modern Latin.

 b) When reading the data back, can we use a bigger buffer than 1000 bytes? This would speed
up the test when run with the client driver. The max length for binary varchar is the maximum
that can be transferred between the server and the client in one go with locators.

Some tiny formatting nits for SQLBinary:
 1) Mix of tabs and spaces on line "throwStreamingIOException(ioe);"
 2) Trailing tab on "byte[] bytes = getBytes();"
 3) Last line of method "throwStreamingIOException" doesn't use tab for indent.


thanks,

> 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: derby-3732_diff.txt, derby-3732_proto_diff.txt, derby-3732_skip2_diff.txt,
derby-3732_skip_diff.txt, 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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