import com.sleepycat.db.*; import java.io.FileNotFoundException;
public void open(String file, String database, int type, int flags, int mode) throws DbException, FileNotFoundException;
The currently supported Berkeley DB file formats (or access methods) are Btree, Hash, Queue, and Recno. The Btree format is a representation of a sorted, balanced tree structure. The Hash format is an extensible, dynamic hashing scheme. The Queue format supports fast access to fixed-length records accessed sequentially or by logical record number. The Recno format supports fixed- or variable-length records, accessed sequentially or by logical record number, and optionally backed by a flat text file.
Storage and retrieval for the Berkeley DB access methods are based on key/data pairs; see Dbt for more information.
The Db.open interface opens the database represented by the file and database arguments for both reading and writing. The file argument is used as the name of an underlying file that will be used to back the database. The database argument is optional, and allows applications to have multiple databases in a single file. Although no database argument needs to be specified, it is an error to attempt to open a second database in a file that was not initially created using a database name. Further, the database argument is not supported by the Queue format.
In-memory databases never intended to be preserved on disk may be created by setting both the file and database arguments to null. Note that in-memory databases can only ever be shared by sharing the single database handle that created them, in circumstances where doing so is safe.
The type argument is of type int, and must be set to one of Db.DB_BTREE, Db.DB_HASH, Db.DB_QUEUE, Db.DB_RECNO, or Db.DB_UNKNOWN. If type is Db.DB_UNKNOWN, the database must already exist and Db.open will automatically determine its type. The Db.get_type method may be used to determine the underlying type of databases opened using Db.DB_UNKNOWN.
The flags and mode arguments specify how files will be opened and/or created if they do not already exist.
The flags value must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values:
The Db.DB_EXCL flag is only meaningful when specified with the Db.DB_CREATE flag.
Threading is always assumed in the Java API, so no special flags are required, and Berkeley DB functions will always behave as if the Db.DB_THREAD flag was specified.
The Db.DB_TRUNCATE flag cannot be transaction-protected, and it is an error to specify it in a transaction-protected environment.
On UNIX systems or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by the access methods are created with mode mode (as described in chmod(2)) and modified by the process' umask value at the time of creation (see umask(2)). If mode is 0, the access methods will use a default mode of readable and writable by both owner and group. On Windows systems, the mode argument is ignored. The group ownership of created files is based on the system and directory defaults, and is not further specified by Berkeley DB.
Calling Db.open is a reasonably expensive operation, and maintaining a set of open databases will normally be preferable to repeatedly opening and closing the database for each new query.
The Db.open method throws an exception that encapsulates a non-zero error value on failure.
The Db.open method may fail and throw an exception encapsulating a non-zero error for the following conditions:
The Db.DB_THREAD flag was specified and fast mutexes are not available for this architecture.
The Db.DB_THREAD flag was specified to Db.open, but was not specified to the DbEnv.open call for the environment in which the Db handle was created.
A backing flat text file was specified with either the Db.DB_THREAD flag or the provided database environment supports transaction processing.
The Db.open method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Db.open method may fail and throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.
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