OutOfMemory Error on continous execution of select statement using COUNT() and
DISTINCT on same connection
----------------------------------------------------------------------------------------------------------
Key: DERBY-756
URL: http://issues.apache.org/jira/browse/DERBY-756
Project: Derby
Type: Bug
Components: Demos/Scripts, JDBC, Network Client, Network Server, SQL
Versions: 10.0.2.1, 10.1.2.1
Environment: Windows XP, Java 1.5.0_05, Derby network server 10.0.2.1,
10.1.2.1, Derby heapsize 128m, IBM Universal JDBC driver
Reporter: Bill Chen
Priority: Critical
The OutOfMemory is thrown when I continously execute a sql statement on an
openned JDBC connection. A PreparedStatement and ResultSet is created on the
connection everytime and close after each execution. I suspect that the bug is
related to function COUNT() with keyword DISTINCT. For example, "select
count(distinct ID) from TEST where FLAG <> 2". It will be fine if DISTINCT is
not used, or select count(*) is used.
The exception like "Exception in thread "DRDAConnThread_2"
java.lang.OutOfMemoryError: Java heap space" could be thrown on Derby side, or
sometimes on client side.
Please find the test code and schema I used for testing:
create table:
CREATE TABLE Test
(
ID BIGINT NOT NULL,
NAME VARCHAR(512) NOT NULL,
FLAG int,
CONSTRAINT PK_ID PRIMARY KEY (ID)
);
insert data:
insert into TEST values (0, 'name0', 0);
insert into TEST values (1, 'name1', 1);
insert into TEST values (2, 'name2', 2);
Java client:
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.DriverManager;
import java.sql.SQLException;
public class DerbyTest
{
static public void main(String args[]) throws Exception
{
Class.forName("com.ibm.db2.jcc.DB2Driver");
Connection conn = null;
try
{
conn =
DriverManager.getConnection("jdbc:derby:net://localhost:1527/testDB", "admin",
"admin");
for (int i = 0; i < 10000000; i++)
{
System.out.println("Query "+i);
String sql = "select count(distinct ID) from TEST where FLAG <>
2";
PreparedStatement pStmt = null;
ResultSet rs = null;
try
{
pStmt = conn.prepareStatement(sql);
rs = pStmt.executeQuery();
if (rs.next())
{
rs.getInt(1);
}
}
catch (SQLException e)
{
e.printStackTrace();
}
finally
{
if (rs != null)
rs.close();
if (pStmt != null)
pStmt.close();
}
}
}
finally
{
if (conn != null)
conn.close();
}
}
}
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