Big Lock in Driver.compileInternal

[Loudongfeng]

Hi, All

I notice that there is a big lock in org.apache.hadoop.hive.ql.Driver
Following is a piece of code from Apache Hive 1.2.0

private static final Object compileMonitor = new Object();

private int compileInternal(String command) {
  int ret;
  synchronized (compileMonitor) {
    ret = compile(command);
  }
...
}

This means HQLs submitted concurrently from clients side will be compiled one 
by one on Hive Server side.
This will cause problem when compile phase is slow.

My question is ,what does this lock protect for? Is it possible to remove it ?

Best Regards
Nemon