code: public void acquireEdgeLock(StaticBuffer key, StaticBuffer column) throws BackendException {
          acquiredLock = true;
          edgeStore.acquireLock(key, column, null, storeTx);
      }
docs: Acquires a lock for the key-column pair on the edge store which ensures that nobody else can take a lock on that
  respective entry for the duration of this lock (but somebody could potentially still overwrite
  the key-value entry without taking a lock).
  The expectedValue defines the value expected to match the value at the time the lock is acquired (or null if it is expected
  that the key-column pair does not exist).
  <p/>
  If this method is called multiple times with the same key-column pair in the same transaction, all but the first invocation are ignored.
  <p/>
  The lock has to be released when the transaction closes (commits or aborts).
  
  @param key           Key on which to lock
  @param column        Column the column on which to lock