@Override
  public boolean isHA() {
    // GEM-207
    return true;
  }
This function can be used by GemFire clients and peers to rollback an existing transaction. A
{@link TransactionId} corresponding to the transaction to be rolledback must be provided as an
argument while invoking this function.<br>

This function should execute only on one server. If the transaction is not hosted on the server
where the function is invoked then this function decides to invoke a
{@link NestedTransactionFunction} which executes on the member where transaction is hosted.<br>

This function returns a single Boolean as result, whose value is <code>Boolean.TRUE</code> if the
transaction rolled back successfully otherwise the return value is
<code>Boolean.FALSE</code>.<br>

To execute this function, it is recommended to use the {@link Execution} obtained by using
TransactionFunctionService. <br>

To summarize, this function should be used as follows:

<pre>
Execution exe = TransactionFunctionService.onTransaction(txId);
List l = (List) exe.execute(rollbackFunction).getResult();
Boolean result = (Boolean) l.get(0);
</pre>

This function is <b>not</b> registered on the cache servers by default, and it is the user's
responsibility to register this function. see {@link FunctionService#registerFunction(Function)}

@since GemFire 6.6.1
geode-dunit/src/main/java/org/apache/geode/internal/cache/RollbackFunction.java