core/src/main/java/com/orientechnologies/orient/core/metadata/schema/OClassImpl.java
public void truncate() throws IOException {
    ODatabaseDocumentInternal db = getDatabase();
    db.checkSecurity(ORule.ResourceGeneric.CLASS, ORole.PERMISSION_UPDATE);

    if (isSubClassOf(OSecurityShared.RESTRICTED_CLASSNAME)) {
      throw new OSecurityException(
          "Class '" + getName() + "' cannot be truncated because has record level security enabled (extends '"
              + OSecurityShared.RESTRICTED_CLASSNAME + "')");
    }

    final OStorage storage = db.getStorage();
    acquireSchemaReadLock();
    try {

      for (int id : clusterIds) {
        OCluster cl = storage.getClusterById(id);
        db.checkForClusterPermissions(cl.getName());
        cl.truncate();
      }
      for (OIndex<?> index : getClassIndexes())
        index.clear();

      Set<OIndex<?>> superclassIndexes = new HashSet<OIndex<?>>();
      superclassIndexes.addAll(getIndexes());
      superclassIndexes.removeAll(getClassIndexes());
      for (OIndex index : superclassIndexes) {
        index.rebuild();
      }
    } finally {
      releaseSchemaReadLock();
    }
  }
public void truncate() throws IOException {
    ODatabaseDocumentInternal db = getDatabase();
    db.checkSecurity(ORule.ResourceGeneric.CLASS, ORole.PERMISSION_UPDATE);

    if (isSubClassOf(OSecurityShared.RESTRICTED_CLASSNAME)) {
      throw new OSecurityException(
          "Class '" + getName() + "' cannot be truncated because has record level security enabled (extends '"
              + OSecurityShared.RESTRICTED_CLASSNAME + "')");
    }

    final OStorage storage = db.getStorage();
    acquireSchemaReadLock();
    try {

      for (int id : clusterIds) {
        OCluster cl = storage.getClusterById(id);
        db.checkForClusterPermissions(cl.getName());
        cl.truncate();
      }
      for (OIndex<?> index : getClassIndexes())
        index.clear();

      Set<OIndex<?>> superclassIndexes = new HashSet<OIndex<?>>();
      superclassIndexes.addAll(getIndexes());
      superclassIndexes.removeAll(getClassIndexes());
      for (OIndex index : superclassIndexes) {
        index.rebuild();
      }
    } finally {
      releaseSchemaReadLock();
    }
  }
Truncates all the clusters the class uses.