Class Db

fe/src/main/java/org/apache/impala/catalog/Db.java:76–660

Internal representation of db-related metadata. Owned by Catalog instance. Not thread safe. Tables are stored in a map from the table name to the table object. They may be loaded 'eagerly' at construction or 'lazily' on first reference. Tables are accessed via getTable which may trigger a metadata

 *
 */
public class Db extends CatalogObjectImpl implements FeDb {
  private static final Logger LOG = LoggerFactory.getLogger(Db.class);
  // TODO: We should have a consistent synchronization model for Db and Table
  // Right now, we synchronize functions and thriftDb_ object in-place and do
  // not take read lock on catalogVersion. See IMPALA-8366 for details
  private final AtomicReference<TDatabase> thriftDb_ = new AtomicReference<>();

  public static final String FUNCTION_INDEX_PREFIX = "impala_registered_function_";

  // Name of the standard system DB. Also used by Hive MetaStore.
  public static final String SYS = "sys";

  // Hive metastore imposes a limit of 4000 bytes on the key and value strings
  // in DB parameters map. We need ensure that this limit isn't crossed
  // while serializing functions to the metastore.
  private static final int HIVE_METASTORE_DB_PARAM_LIMIT_BYTES = 4000;

  // Table metadata cache.
  private final CatalogObjectCache<Table> tableCache_;

  // All of the registered user functions. The key is the user facing name (e.g. "myUdf"),
  // and the values are all the overloaded variants (e.g. myUdf(double), myUdf(string))
  // This includes both UDFs and UDAs. Updates are made thread safe by synchronizing
  // on this map. When a new Db object is initialized, this list is updated with the
  // UDF/UDAs already persisted, if any, in the metastore DB. Functions are sorted in a
  // canonical order defined by FunctionResolutionOrder.
  private final Map<String, List<Function>> functions_;

  // If true, this database is an Impala system database.
  // (e.g. can't drop it, can't add tables to it, etc).
  private boolean isSystemDb_ = false;

  // tracks the in-flight metastore events for this db
  // Also used as a monitor object to synchronize access to it to avoid blocking on table
  // lock during self-event check. If both this and dbLock_ or catalog version lock are
  // taken, inFlightEvents_ must be the last to avoid deadlock.
  private final InFlightEvents inFlightEvents_ = new InFlightEvents();

  // lock to make sure modifications to the Db object are atomically done along with
  // its associated HMS operation (eg. alterDbOwner or commentOnDb)
  private final ReentrantLock dbLock_ = new ReentrantLock();

  // if this Db is created by catalogd and if events processing is ACTIVE then
  // this field represents the event id pertaining to the creation of this database
  // in hive metastore. Defaults to -1 for already existing databases or if events
  // processing is disabled.
  private long createEventId_ = -1;

  // this field represents the last event id in metastore upto which this db is synced
  // It is used if the flag sync_to_latest_event_on_ddls is set to true.
  // Making it as volatile so that read and write of this variable are thread safe.
  // As an example, EventProcessor can check if it needs to process a db event or not
  // by reading this flag and without acquiring read lock on db object
  private volatile long lastSyncedEventId_ = -1;

  // Flag used by CatalogServiceCatalog to mark if this Db is already removed or not.
  // Should only be used by CatalogServiceCatalog.
  private volatile boolean isRemoved_ = false;