Lock not being released properly, possibly related to occurence of lock
escalation
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Key: DERBY-94
URL: http://nagoya.apache.org/jira/browse/DERBY-94
Project: Derby
Type: Bug
Components: Store
Versions: 10.0.2.1
Environment: all
Reporter: Sunitha Kambhampati
In the following scenario:
<code snippet>
String sel = "select * from t1 FOR UPDATE of i2";
PreparedStatement ps1 = conn.prepareStatement (sel);
int val = 300;
ps1.setMaxRows(val);
ResultSet rs = ps1.executeQuery();
String ins = "Update t1 set i2=? WHERE CURRENT OF
"+rs.getCursorName() ;
PreparedStatement ps2 = conn.prepareStatement(ins);
ps2.setInt(1,iteration);
while(rs.next())
{
ps2.executeUpdate();
};
// print lock table information
System.out.println("Lock Table before commit transaction");
printLockTable(conn);
conn.commit();
<end code snippet>
Running the above transaction twice causes a lock timeout the second time.
It seems like locks are not being released properly on the table even after the
transaction commits and the connection is closed. Also, this condition seems to
happen only when lock escalation to table lock occurs. By increasing lock
escalation threshold to prevent lock escalation and with only row level
locking, the locks are released properly.
I printed out the locks information and see a U row level lock on the table ,
and also a table level lock as a result of lock escalation. After commit, and
resultset being closed, the U row level lock is not released. Thus in the
second iteration of the test, the unreleased U row level lock causes a lock
timeout to happen. In case of the second iteration of the test, the lock table
shows the previous U row lock with a null transaction id. This is not right.
The transactions are running at the default isolation level ( read committed).
By default, the lock escalation threshold is set to 5000
http://incubator.apache.org/derby/manuals/tuning/perf80.html#IDX547
I will be attaching the program for reproduction. To reproduce the problem
with less number of rows in the table, please run the program with the
following derby properties set
derby.locks.deadlockTrace=true
derby.locks.escalationThreshold=110
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