core/src/main/java/com/orientechnologies/orient/core/sql/OCommandExecutorSQLDropCluster.java
public Object execute(final Map<Object, Object> iArgs) {
    if (clusterName == null)
      throw new OCommandExecutionException("Cannot execute the command because it has not been parsed yet");

    final ODatabaseDocumentInternal database = getDatabase();

    // CHECK IF ANY CLASS IS USING IT
    final int clusterId = database.getStorage().getClusterIdByName(clusterName);
    for (OClass iClass : database.getMetadata().getSchema().getClasses()) {
      for (int i : iClass.getClusterIds()) {
        if (i == clusterId)
          // IN USE
          return false;
      }
    }

    // REMOVE CACHE OF COMMAND RESULTS IF ACTIVE
    database.getMetadata().getCommandCache().invalidateResultsOfCluster(clusterName);

    database.dropCluster(clusterId, true);
    return true;
  }
public Object execute(final Map<Object, Object> iArgs) {
    if (clusterName == null)
      throw new OCommandExecutionException("Cannot execute the command because it has not been parsed yet");

    final ODatabaseDocumentInternal database = getDatabase();

    // CHECK IF ANY CLASS IS USING IT
    final int clusterId = database.getStorage().getClusterIdByName(clusterName);
    for (OClass iClass : database.getMetadata().getSchema().getClasses()) {
      for (int i : iClass.getClusterIds()) {
        if (i == clusterId)
          // IN USE
          return false;
      }
    }

    // REMOVE CACHE OF COMMAND RESULTS IF ACTIVE
    database.getMetadata().getCommandCache().invalidateResultsOfCluster(clusterName);

    database.dropCluster(clusterId, true);
    return true;
  }
Execute the DROP CLUSTER.