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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6096) DataTypeDescriptor.estimatedMemoryUsage() has no case for BLOB or CLOB so would underestimate memory usage for those types at zero
Date Tue, 05 Mar 2013 14:27:13 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593431#comment-13593431

Kathey Marsden commented on DERBY-6096:

I am out today but thought I would post where I was on trying to get a reproduction for the
memory usage with Clob hash joins.  I created this fixture in memory.ClobMemTest.  At one
point I was getting an OOM on the query if derby.language.maxMemoryPerTable wasn't set running
-Xmx64M   but then started cleaning up and it no longer occurs.  I will look more closely
tomorrow but just wanted to post where I am and get input on how to reproduce.

    public void testClobHashJoin() throws SQLException {
        Statement s = createStatement();
        try {
            // Setting maxMemoryPerTable to 0 allows the query to complete
            // until OOM is fixed.
            //println("setSystemProperty(\"derby.language.maxMemoryPerTable\", \"0\")");
            //setSystemProperty("derby.language.maxMemoryPerTable", "0");
            s.executeUpdate("CREATE TABLE T1 (ID INT , NAME VARCHAR(30))");
            s.executeUpdate("CREATE TABLE T2 (ID INT , CDATA CLOB(1G))");
            PreparedStatement ps = prepareStatement("insert into t1 values(?,?)");
            PreparedStatement ps2 = prepareStatement("insert into t2 values(?,?)");
            // insert 8 long rows
            for (int i = 1; i <= 8; i++) {
                ps.setInt(1, i);
                ps.setString(2, "name" + i);
                ps2.setInt(1, i);
                ps2.setCharacterStream(2, new LoopingAlphabetReader(
                        LONG_CLOB_LENGTH), LONG_CLOB_LENGTH);
            // Do a query. Force a hash join
            PreparedStatement ps3 = prepareStatement("SELECT * FROM t1, t2 --DERBY-PROPERTIES
                    + "where t1.id = t2.id AND t1.id < 8  ");
            ResultSet rs = ps3.executeQuery();
            int i = 0;
            for (; rs.next(); i++) {
                // just fetch don't materialize results
                // derby.tests.trace prints memory usage
                println("TotalMemory:" + Runtime.getRuntime().totalMemory()
                        + " " + "Free Memory:"
                        + Runtime.getRuntime().freeMemory());
            assertEquals("Expected 7 rows, got + i", 7, i);
            RuntimeStatisticsParser p = SQLUtilities
        } finally {

> DataTypeDescriptor.estimatedMemoryUsage()  has no case for BLOB or CLOB so would underestimate
memory usage for those types at zero
> -----------------------------------------------------------------------------------------------------------------------------------
>                 Key: DERBY-6096
>                 URL: https://issues.apache.org/jira/browse/DERBY-6096
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:,,,,,,,,,
>            Reporter: Kathey Marsden
> In discussion on derby-dev regarding how much memory is used for hash joins, Knut noted:
> I haven't verified, but I think HashJoinStrategy uses
> DataTypeDescriptor.estimatedMemoryUsage() to estimate how much memory
> the hash table will consume. That method has no case for BLOB or CLOB,
> so it looks as if it will return zero for LOB columns. If that's so, it
> will definitely overestimate how many rows fits in maxMemoryPerTable
> kilobytes if the rows contain LOBs.
> DataTypeDescriptor.estimatedMemoryUsage() should be updated to include BLOB and CLOB
and we should try verify if this theory is correct with a reproduction.

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