org.mapdb

Class TxEngine

java.lang.Object

org.mapdb.EngineWrapper

org.mapdb.TxEngine

All Implemented Interfaces:

Engine

public class TxEngine
extends EngineWrapper

Naive implementation of Snapshots on top of StorageEngine. On update it takes old value and stores it aside.

TODO merge snapshots down with Storage for best performance

Author:

Jan Kotek

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	TxEngine.Tx

Nested classes/interfaces inherited from class org.mapdb.EngineWrapper

EngineWrapper.CloseOnJVMShutdown, EngineWrapper.ImmutabilityCheckEngine, EngineWrapper.ReadOnlyEngine, EngineWrapper.SerializerCheckEngineWrapper, EngineWrapper.SynchronizedEngineWrapper

Field Summary

Fields

Modifier and Type	Field and Description
protected ReentrantReadWriteLock	commitLock
protected boolean	fullTx
protected ReentrantReadWriteLock[]	locks
protected int	PREALLOC_RECID_SIZE
protected Queue<Long>	preallocRecids
protected static Object	TOMBSTONE
protected ReferenceQueue<TxEngine.Tx>	txQueue
protected Set<Reference<TxEngine.Tx>>	txs
protected boolean	uncommitedData

Fields inherited from class org.mapdb.EngineWrapper

CLOSED

Fields inherited from interface org.mapdb.Engine

CATALOG_RECID, CHECK_RECORD, CLASS_INFO_RECID, LAST_RESERVED_RECID

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	TxEngine(Engine engine, boolean fullTx)

Method Summary

Modifier and Type	Method and Description
boolean	canSnapshot()
protected void	cleanTxQueue()
void	close() Close store/cache.
void	commit() Makes all changes made since the previous commit/rollback permanent.
<A> boolean	compareAndSwap(long recid, A expectedOldValue, A newValue, Serializer<A> serializer) Updates existing record in atomic (Compare And Swap) manner.
static Engine	createSnapshotFor(Engine engine)
<A> void	delete(long recid, Serializer<A> serializer) Remove existing record from store/cache Recid must be a number returned by 'put' method.
<A> A	get(long recid, Serializer<A> serializer) Get existing record.
long	preallocate() Preallocates recid for not yet created record.
void	preallocate(long[] recids) Preallocates recids for not yet created record.
protected Long	preallocRecidTake()
<A> long	put(A value, Serializer<A> serializer) Insert new record.
void	rollback() Undoes all changes made in the current transaction.
Engine	snapshot() Returns read-only snapshot of data in Engine.
protected void	superCommit()
protected <A> void	superDelete(long recid, Serializer<A> serializer)
protected <A> A	superGet(long recid, Serializer<A> serializer)
protected <A> void	superUpdate(long recid, A value, Serializer<A> serializer)
<A> void	update(long recid, A value, Serializer<A> serializer) Update existing record with new value.

Methods inherited from class org.mapdb.EngineWrapper

canRollback, checkClosed, clearCache, closeListenerRegister, closeListenerUnregister, compact, getSerializerPojo, getWrappedEngine, isClosed, isReadOnly

Methods inherited from class java.lang.Object

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

Field Detail

TOMBSTONE

protected static final Object TOMBSTONE

commitLock

protected final ReentrantReadWriteLock commitLock

locks

protected final ReentrantReadWriteLock[] locks

uncommitedData

protected volatile boolean uncommitedData

txs

protected Set<Reference<TxEngine.Tx>> txs

txQueue

protected ReferenceQueue<TxEngine.Tx> txQueue

fullTx

protected final boolean fullTx

preallocRecids

protected final Queue<Long> preallocRecids

PREALLOC_RECID_SIZE

protected final int PREALLOC_RECID_SIZE

See Also:

Constant Field Values

Constructor Detail

TxEngine

protected TxEngine(Engine engine,
                   boolean fullTx)

Method Detail

preallocRecidTake

protected Long preallocRecidTake()

createSnapshotFor

public static Engine createSnapshotFor(Engine engine)

canSnapshot

public boolean canSnapshot()

Specified by:

canSnapshot in interface Engine

Overrides:

canSnapshot in class EngineWrapper

Returns:

true if engine can create read-only snapshots

snapshot

public Engine snapshot()

Description copied from interface: Engine

Returns read-only snapshot of data in Engine.

Specified by:

snapshot in interface Engine

Overrides:

snapshot in class EngineWrapper

See Also:

EngineWrapper.canSnapshot()

cleanTxQueue

protected void cleanTxQueue()

preallocate

public long preallocate()

Description copied from interface: Engine

Preallocates recid for not yet created record. It does not insert any data into it.

Specified by:

preallocate in interface Engine

Overrides:

preallocate in class EngineWrapper

Returns:

new recid

preallocate

public void preallocate(long[] recids)

Description copied from interface: Engine

Preallocates recids for not yet created record. It does not insert any data into it. This is done in batch of given size (determied by size of array in argument)

Specified by:

preallocate in interface Engine

Overrides:

preallocate in class EngineWrapper

Parameters:

recids - array to put result into

put

public <A> long put(A value,
                    Serializer<A> serializer)

Description copied from interface: Engine

Insert new record.

Specified by:

put in interface Engine

Overrides:

put in class EngineWrapper

Parameters:

value - records to be added

serializer - used to convert record into/from binary form

Returns:

recid (record identifier) under which record is stored.

get

public <A> A get(long recid,
                 Serializer<A> serializer)

Description copied from interface: Engine

Get existing record.

Recid must be a number returned by 'put' method. Behaviour for invalid recid (random number or already deleted record) is not defined, typically it returns null or throws 'EndOfFileException'

Specified by:

get in interface Engine

Overrides:

get in class EngineWrapper

Parameters:

recid - (record identifier) under which record was persisted

serializer - used to deserialize record from binary form

Returns:

record matching given recid, or null if record is not found under given recid.

update

public <A> void update(long recid,
                       A value,
                       Serializer<A> serializer)

Description copied from interface: Engine

Update existing record with new value.

Recid must be a number returned by 'put' method. Behaviour for invalid recid (random number or already deleted record) is not defined, typically it throws 'EndOfFileException', but it may also corrupt store.

Specified by:

update in interface Engine

Overrides:

update in class EngineWrapper

Parameters:

recid - (record identifier) under which record was persisted.

value - new record value to be stored

serializer - used to serialize record into binary form

compareAndSwap

public <A> boolean compareAndSwap(long recid,
                                  A expectedOldValue,
                                  A newValue,
                                  Serializer<A> serializer)

Description copied from interface: Engine

Updates existing record in atomic (Compare And Swap) manner. Value is modified only if old value matches expected value. There are three ways to match values, MapDB may use any of them:

1. Equality check oldValue==expectedOldValue when old value is found in instance cache
2. Deserializing oldValue using serializer and checking oldValue.equals(expectedOldValue)
3. Serializing expectedOldValue using serializer and comparing binary array with already serialized oldValue

Recid must be a number returned by 'put' method. Behaviour for invalid recid (random number or already deleted record) is not defined, typically it throws 'EndOfFileException', but it may also corrupt store.

Specified by:

compareAndSwap in interface Engine

Overrides:

compareAndSwap in class EngineWrapper

Parameters:

recid - (record identifier) under which record was persisted.

expectedOldValue - old value to be compared with existing record

newValue - to be written if values are matching

serializer - used to serialize record into binary form

Returns:

true if values matched and newValue was written

delete

public <A> void delete(long recid,
                       Serializer<A> serializer)

Description copied from interface: Engine

Remove existing record from store/cache

Recid must be a number returned by 'put' method. Behaviour for invalid recid (random number or already deleted record) is not defined, typically it throws 'EndOfFileException', but it may also corrupt store.

Specified by:

delete in interface Engine

Overrides:

delete in class EngineWrapper

Parameters:

recid - (record identifier) under which was record persisted

serializer - which may be used in some circumstances to deserialize and store old object

close

public void close()

Description copied from interface: Engine

Close store/cache. This method must be called before JVM exits to flush all caches and prevent store corruption. Also it releases resources used by MapDB (disk, memory..).

Engine can no longer be used after this method was called. If Engine is used after closing, it may throw any exception including NullPointerException

There is an configuration option DBMaker.closeOnJvmShutdown() which uses shutdown hook to automatically close Engine when JVM shutdowns.

Specified by:

close in interface Engine

Overrides:

close in class EngineWrapper

commit

public void commit()

Description copied from interface: Engine

Makes all changes made since the previous commit/rollback permanent. In transactional mode (on by default) it means creating journal file and replaying it to storage. In other modes it may flush disk caches or do nothing at all (check your config options)

Specified by:

commit in interface Engine

Overrides:

commit in class EngineWrapper

rollback

public void rollback()

Description copied from interface: Engine

Undoes all changes made in the current transaction. If transactions are disabled it throws UnsupportedOperationException.

Specified by:

rollback in interface Engine

Overrides:

rollback in class EngineWrapper

superCommit

protected void superCommit()

superUpdate

protected <A> void superUpdate(long recid,
                               A value,
                               Serializer<A> serializer)

superDelete

protected <A> void superDelete(long recid,
                               Serializer<A> serializer)

superGet

protected <A> A superGet(long recid,
                         Serializer<A> serializer)