Berkeley DB Java Edition
version 1.7.0

com.sleepycat.je
Class Environment

java.lang.Object
  extended bycom.sleepycat.je.Environment

public class Environment
extends Object

A database environment. Environments include support for some or all of caching, locking, logging and transactions.

To open an existing environment with default attributes the application may use a default environment configuration object or null:

    // Open an environment handle with default attributes.
    Environment env = new Environment(home, new EnvironmentConfig());

or

    Environment env = new Environment(home, null);

Note that many Environment objects may access a single environment.

To create an environment or customize attributes, the application should customize the configuration class. For example:

    EnvironmentConfig envConfig = new EnvironmentConfig();
    envConfig.setTransactional(true);
    envConfig.setAllowCreate(true);
    envConfig.setCacheSize(1000000);
    

Environment newlyCreatedEnv = new Environment(home, envConfig);

Note that environment configuration parameters can also be set through the <environment home>/je.properties file. This file takes precedence over any programmatically specified configuration parameters so that configuration changes can be made without recompiling. Environment configuration follows this order of precedence:

  1. Configuration parameters specified in <environment home>/je.properties take first precedence.
  2. Configuration parameters set in the EnvironmentConfig object used at Environment construction are next.
  3. Any configuration parameters not set by the application are set to system defaults, described in the example.properties file included at the top of the distribution.

An environment handle is an Environment instance. More than one Environment instance may be created for the same physical directory, which is the same as saying that more than one Environment handle may be open at one time for a given environment.

The Environment handle should not be closed while any other handle remains open that is using it as a reference (for example, Database or Transaction. Once Environment.close is called, this object may not be accessed again, regardless of whether or not it throws an exception.


Constructor Summary
Environment(File envHome, EnvironmentConfig envConfig)
          Create a database environment handle.
 
Method Summary
 Transaction beginTransaction(Transaction parent, TransactionConfig txnConfig)
          Create a new transaction in the database environment.
 void checkpoint(CheckpointConfig checkpointConfig)
          Synchronously checkpoint the database environment.
 int cleanLog()
          Synchronously invoke database environment log cleaning.
 void close()
          The Environment.close method closes the Berkeley DB environment.
 void compress()
          Synchronously invoke the compressor mechanism which compacts in memory data structures after delete operations.
 void evictMemory()
          Synchronously invoke the mechanism for keeping memory usage within the cache size boundaries.
 EnvironmentConfig getConfig()
          Return this object's configuration.
 List getDatabaseNames()
          Return a List of database names for the database environment.
 File getHome()
          Return the database environment's home directory.
 LockStats getLockStats(StatsConfig config)
          Return the database environment's locking statistics.
 EnvironmentMutableConfig getMutableConfig()
          Return database environment attributes.
 EnvironmentStats getStats(StatsConfig config)
          Return the general database environment statistics.
 TransactionStats getTransactionStats(StatsConfig config)
          Return the database environment's transactional statistics.
 Database openDatabase(Transaction txn, String databaseName, DatabaseConfig dbConfig)
          Open, and optionally create, a Database.
 SecondaryDatabase openSecondaryDatabase(Transaction txn, String databaseName, Database primaryDatabase, SecondaryConfig secConfig)
          Open and optionally create a SecondaryDatabase.
 void removeDatabase(Transaction txn, String databaseName)
          Remove a database.
 void renameDatabase(Transaction txn, String databaseName, String newName)
          Rename a database.
 void setMutableConfig(EnvironmentMutableConfig envMutableConfig)
          Set database environment attributes.
 void sync()
          Synchronously flush database environment databases to stable storage.
 long truncateDatabase(Transaction txn, String databaseName, boolean returnCount)
          Empty the database, discarding all records it contains.
 boolean verify(VerifyConfig verifyConfig, PrintStream out)
          Return if the database environment is consistent and correct.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Environment

public Environment(File envHome,
                   EnvironmentConfig envConfig)
            throws DatabaseException
Create a database environment handle.

Parameters:
envHome - The database environment's home directory.

envConfig - The database environment attributes. If null, default attributes are used.

Throws:
IllegalArgumentException - if an invalid parameter was specified.

DatabaseException - if a failure occurs.
Method Detail

getHome

public File getHome()
             throws DatabaseException
Return the database environment's home directory.

Returns:
The database environment's home directory.

Throws:
DatabaseException - if a failure occurs.

getConfig

public EnvironmentConfig getConfig()
                            throws DatabaseException
Return this object's configuration.

Returns:
This object's configuration.

Throws:
DatabaseException - if a failure occurs.

beginTransaction

public Transaction beginTransaction(Transaction parent,
                                    TransactionConfig txnConfig)
                             throws DatabaseException
Create a new transaction in the database environment.

Transaction handles are free-threaded; transactions handles may be used concurrently by multiple threads.

Cursors may not span transactions; that is, each cursor must be opened and closed within a single transaction. The parent parameter is a placeholder for nested transactions, and must currently be null.

Parameters:
txnConfig - The transaction attributes. If null, default attributes are used.

Returns:
The newly created transaction's handle.

Throws:
DatabaseException - if a failure occurs.

checkpoint

public void checkpoint(CheckpointConfig checkpointConfig)
                throws DatabaseException
Synchronously checkpoint the database environment.

This is an optional action for the application since this activity is, by default, handled by a database environment owned background thread.

Parameters:
checkpointConfig - The checkpoint attributes. If null, default attributes are used.

Throws:
DatabaseException - if a failure occurs.

getLockStats

public LockStats getLockStats(StatsConfig config)
                       throws DatabaseException
Return the database environment's locking statistics.

Parameters:
config - The locking statistics attributes. If null, default attributes are used.

Returns:
The database environment's locking statistics.

Throws:
DatabaseException - if a failure occurs.

getTransactionStats

public TransactionStats getTransactionStats(StatsConfig config)
                                     throws DatabaseException
Return the database environment's transactional statistics.

Parameters:
config - The transactional statistics attributes. If null, default attributes are used.

Returns:
The database environment's transactional statistics.

Throws:
DatabaseException - if a failure occurs.

close

public void close()
           throws DatabaseException
The Environment.close method closes the Berkeley DB environment.

When the last environment handle is closed, allocated resources are freed, and daemon threads are stopped.

The Environment handle should not be closed while any other handle that refers to it is not yet closed; for example, database environment handles must not be closed while database handles remain open, or transactions in the environment have not yet committed or aborted. Specifically, this includes Database, Cursor and Transaction handles.

In multithreaded applications, only a single thread should call Environment.close. Other callers will see a DatabaseException complaining that the handle is already closed.

After Environment.close has been called, regardless of its return, the Berkeley DB environment handle may not be accessed again.

Throws:
DatabaseException - if a failure occurs.

openDatabase

public Database openDatabase(Transaction txn,
                             String databaseName,
                             DatabaseConfig dbConfig)
                      throws DatabaseException
Open, and optionally create, a Database.

Parameters:
txn - For a transactional database, an explicit transaction may be specified, or null may be specified to use auto-commit. For a non-transactional database, null must be specified.

databaseName - The name of the database.

dbConfig - The database attributes. If null, default attributes are used.

Returns:
Database handle.

Throws:
DatabaseNotFoundException - if the database file does not exist.

DatabaseException - if a failure occurs.

openSecondaryDatabase

public SecondaryDatabase openSecondaryDatabase(Transaction txn,
                                               String databaseName,
                                               Database primaryDatabase,
                                               SecondaryConfig secConfig)
                                        throws DatabaseException
Open and optionally create a SecondaryDatabase.

Parameters:
txn - For a transactional database, an explicit transaction may be specified, or null may be specified to use auto-commit. For a non-transactional database, null must be specified.

databaseName - The name of the database.

primaryDatabase - the primary database with which the secondary database will be associated. The primary database must not be configured for duplicates.

secConfig - The secondary database attributes. If null, default attributes are used.

Returns:
Database handle.

Throws:
DatabaseNotFoundException - if the database file does not exist.

DatabaseException - if a failure occurs.

removeDatabase

public void removeDatabase(Transaction txn,
                           String databaseName)
                    throws DatabaseException
Remove a database.

Applications should never remove databases with open Database handles.

Parameters:
txn - For a transactional environment, an explicit transaction may be specified or null may be specified to use auto-commit. For a non-transactional environment, null must be specified.

databaseName - The database to be removed.

Throws:
DeadlockException - if the operation was selected to resolve a deadlock.

DatabaseNotFoundException - if the database file does not exist.

DatabaseException - if a failure occurs.

renameDatabase

public void renameDatabase(Transaction txn,
                           String databaseName,
                           String newName)
                    throws DatabaseException
Rename a database.

Applications should never rename databases with open Database handles.

Parameters:
txn - For a transactional environment, an explicit transaction may be specified or null may be specified to use auto-commit. For a non-transactional environment, null must be specified.

databaseName - The new name of the database.

Throws:
DeadlockException - if the operation was selected to resolve a deadlock.

DatabaseNotFoundException - if the database file does not exist.

DatabaseException - if a failure occurs.

truncateDatabase

public long truncateDatabase(Transaction txn,
                             String databaseName,
                             boolean returnCount)
                      throws DatabaseException
Empty the database, discarding all records it contains.

When called on a database configured with secondary indices, the application is responsible for also truncating all associated secondary indices.

Applications should never truncate databases with open Database handles.

Parameters:
txn - For a transactional environment, an explicit transaction may be specified or null may be specified to use auto-commit. For a non-transactional environment, null must be specified.

databaseName - The database to be truncated.

returnCount - If true, count and return the number of records discarded.

Returns:
The number of records discarded, or -1 if returnCount is false.

Throws:
DeadlockException - if the operation was selected to resolve a deadlock.

DatabaseNotFoundException - if the database file does not exist.

DatabaseException - if a failure occurs.

sync

public void sync()
          throws DatabaseException
Synchronously flush database environment databases to stable storage.

Throws:
DatabaseException - if a failure occurs.

cleanLog

public int cleanLog()
             throws DatabaseException
Synchronously invoke database environment log cleaning. This method is called periodically by the cleaner daemon thread.

Zero or more log files will be cleaned as necessary to bring the disk space utilization of the environment above the configured minimum utilization threshold. The threshold is determined by the je.cleaner.minUtilization configuration setting.

Note that the cleaned files will not deleted (or renamed) until a checkpoint occurs, and at least N files have been cleaned by the start of the checkpoint. N is determined by the je.cleaner.minFilesToDelete configuration setting. Such a checkpoint must flush all dirty internal nodes, and is therefore more expensive than a standard checkpoint.

This is an optional action for the application since this activity is, by default, handled by a database environment owned background thread.

Returns:
The number of log files that were cleaned, and that will be deleted (or renamed) when a qualifying checkpoint occurs.

Throws:
DatabaseException - if a failure occurs.

evictMemory

public void evictMemory()
                 throws DatabaseException
Synchronously invoke the mechanism for keeping memory usage within the cache size boundaries.

This is an optional action for the application since this activity is, by default, handled by a database environment owned background thread.

Throws:
DatabaseException - if a failure occurs.

compress

public void compress()
              throws DatabaseException
Synchronously invoke the compressor mechanism which compacts in memory data structures after delete operations.

This is an optional action for the application since this activity is, by default, handled by a database environment owned background thread.

Throws:
DatabaseException - if a failure occurs.

setMutableConfig

public void setMutableConfig(EnvironmentMutableConfig envMutableConfig)
                      throws DatabaseException
Set database environment attributes.

Attributes only apply to a specific Environment object and are not necessarily shared by other Environment objects accessing this database environment.

Parameters:
envMutableConfig - The database environment attributes. If null, default attributes are used.

Throws:
DatabaseException - if a failure occurs.

getMutableConfig

public EnvironmentMutableConfig getMutableConfig()
                                          throws DatabaseException
Return database environment attributes.

Returns:
Environment attributes

Throws:
DatabaseException - if a failure occurs.

getStats

public EnvironmentStats getStats(StatsConfig config)
                          throws DatabaseException
Return the general database environment statistics.

Parameters:
config - The general statistics attributes. If null, default attributes are used.

Returns:
The general database environment statistics.

Throws:
DatabaseException - if a failure occurs.

getDatabaseNames

public List getDatabaseNames()
                      throws DatabaseException
Return a List of database names for the database environment.

Each element in the list is a String.

Returns:
A List of database names for the database environment.

Throws:
DatabaseException - if a failure occurs.

verify

public boolean verify(VerifyConfig verifyConfig,
                      PrintStream out)
               throws DatabaseException
Return if the database environment is consistent and correct.

Verification is an expensive operation that should normally only be used for troubleshooting and debugging.

Parameters:
verifyConfig - The verification attributes. If null, default attributes are used.

out - The stream to which verification debugging information is written.

Returns:
If the database environment is consistent and correct.

Throws:
DatabaseException - if a failure occurs.

Berkeley DB Java Edition
version 1.7.0

Copyright (c) 1996-2004 Sleepycat Software, Inc. - All rights reserved.