jdbm.recman

Class BaseRecordManager

java.lang.Object

jdbm.recman.BaseRecordManager

All Implemented Interfaces:

RecordManager

public final class BaseRecordManager
extends Object
implements RecordManager

This class manages records, which are uninterpreted blobs of data. The set of operations is simple and straightforward: you communicate with the class using long "rowids" and byte[] data blocks. Rowids are returned on inserts and you can stash them away someplace safe to be able to get back to them. Data blocks can be as long as you wish, and may have lengths different from the original when updating.

Operations are synchronized, so that only one of them will happen concurrently even if you hammer away from multiple threads. Operations are made atomic by keeping a transaction log which is recovered after a crash, so the operations specified by this interface all have ACID properties.

You identify a file by just the name. The package attaches .db for the database file, and .lg for the transaction log. The transaction log is synchronized regularly and then restarted, so don't worry if you see the size going up and down.

Author:

Alex Boisvert, Cees de Groot

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	DEBUG Static debugging flag
static int	NAME_DIRECTORY_ROOT Reserved slot for name directory.

Constructor Summary

Constructors

Constructor and Description
BaseRecordManager(String filename) Creates a record manager for the indicated file

Method Summary

Modifier and Type	Method and Description
void	close() Closes the record manager.
void	commit() Commit (make persistent) all changes since beginning of transaction.
void	delete(long recid) Deletes a record.
void	disableTransactions() Switches off transactions for the record manager.
Object	fetch(long recid) Fetches a record using standard java object serialization.
Object	fetch(long recid, Serializer serializer) Fetches a record using a custom serializer.
long	getNamedObject(String name) Obtain the record id of a named object.
long	getRoot(int id) Returns the indicated root rowid.
int	getRootCount() Returns the number of slots available for "root" rowids.
TransactionManager	getTransactionManager() Get the underlying Transaction Manager
long	insert(Object obj) Inserts a new record using standard java object serialization.
long	insert(Object obj, Serializer serializer) Inserts a new record using a custom serializer.
void	rollback() Rollback (cancel) all changes since beginning of transaction.
void	setNamedObject(String name, long recid) Set the record id of a named object.
void	setRoot(int id, long rowid) Sets the indicated root rowid.
void	update(long recid, Object obj) Updates a record using standard java object serialization.
void	update(long recid, Object obj, Serializer serializer) Updates a record using a custom serializer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NAME_DIRECTORY_ROOT

public static final int NAME_DIRECTORY_ROOT

Reserved slot for name directory.

See Also:

Constant Field Values

DEBUG

public static final boolean DEBUG

Static debugging flag

See Also:

Constant Field Values

Constructor Detail

BaseRecordManager

public BaseRecordManager(String filename)
                  throws IOException

Creates a record manager for the indicated file

Throws:

IOException - when the file cannot be opened or is not a valid file content-wise.

Method Detail

getTransactionManager

public TransactionManager getTransactionManager()
                                         throws IOException

Get the underlying Transaction Manager

Throws:

IOException

disableTransactions

public void disableTransactions()

Switches off transactions for the record manager. This means that a) a transaction log is not kept, and b) writes aren't synch'ed after every update. This is useful when batch inserting into a new database.

Only call this method directly after opening the file, otherwise the results will be undefined.

close

public void close()
           throws IOException

Closes the record manager.

Specified by:

close in interface RecordManager

Throws:

IOException - when one of the underlying I/O operations fails.

insert

public long insert(Object obj)
            throws IOException

Inserts a new record using standard java object serialization.

Specified by:

insert in interface RecordManager

Parameters:

obj - the object for the new record.

Returns:

the rowid for the new record.

Throws:

IOException - when one of the underlying I/O operations fails.

insert

public long insert(Object obj,
                   Serializer serializer)
            throws IOException

Inserts a new record using a custom serializer.

Specified by:

insert in interface RecordManager

Parameters:

obj - the object for the new record.

serializer - a custom serializer

Returns:

the rowid for the new record.

Throws:

IOException - when one of the underlying I/O operations fails.

delete

public void delete(long recid)
            throws IOException

Deletes a record.

Specified by:

delete in interface RecordManager

Parameters:

recid - the rowid for the record that should be deleted.

Throws:

IOException - when one of the underlying I/O operations fails.

update

public void update(long recid,
                   Object obj)
            throws IOException

Updates a record using standard java object serialization.

Specified by:

update in interface RecordManager

Parameters:

recid - the recid for the record that is to be updated.

obj - the new object for the record.

Throws:

IOException - when one of the underlying I/O operations fails.

update

public void update(long recid,
                   Object obj,
                   Serializer serializer)
            throws IOException

Updates a record using a custom serializer.

Specified by:

update in interface RecordManager

Parameters:

recid - the recid for the record that is to be updated.

obj - the new object for the record.

serializer - a custom serializer

Throws:

IOException - when one of the underlying I/O operations fails.

fetch

public Object fetch(long recid)
             throws IOException

Fetches a record using standard java object serialization.

Specified by:

fetch in interface RecordManager

Parameters:

recid - the recid for the record that must be fetched.

Returns:

the object contained in the record.

Throws:

IOException - when one of the underlying I/O operations fails.

fetch

public Object fetch(long recid,
                    Serializer serializer)
             throws IOException

Fetches a record using a custom serializer.

Specified by:

fetch in interface RecordManager

Parameters:

recid - the recid for the record that must be fetched.

serializer - a custom serializer

Returns:

the object contained in the record.

Throws:

IOException - when one of the underlying I/O operations fails.

getRootCount

public int getRootCount()

Returns the number of slots available for "root" rowids. These slots can be used to store special rowids, like rowids that point to other rowids. Root rowids are useful for bootstrapping access to a set of data.

Specified by:

getRootCount in interface RecordManager

getRoot

public long getRoot(int id)
             throws IOException

Returns the indicated root rowid.

Specified by:

getRoot in interface RecordManager

Throws:

IOException

See Also:

getRootCount()

setRoot

public void setRoot(int id,
                    long rowid)
             throws IOException

Sets the indicated root rowid.

Specified by:

setRoot in interface RecordManager

Throws:

IOException

See Also:

getRootCount()

getNamedObject

public long getNamedObject(String name)
                    throws IOException

Obtain the record id of a named object. Returns 0 if named object doesn't exist.

Specified by:

getNamedObject in interface RecordManager

Throws:

IOException

setNamedObject

public void setNamedObject(String name,
                           long recid)
                    throws IOException

Set the record id of a named object.

Specified by:

setNamedObject in interface RecordManager

Throws:

IOException

commit

public void commit()
            throws IOException

Commit (make persistent) all changes since beginning of transaction.

Specified by:

commit in interface RecordManager

Throws:

IOException

rollback

public void rollback()
              throws IOException

Rollback (cancel) all changes since beginning of transaction.

Specified by:

rollback in interface RecordManager

Throws:

IOException