org.h2.dev.store.btree
Class MVStore

java.lang.Object
  org.h2.dev.store.btree.MVStore

public class MVStore
extends java.lang.Object

A persistent storage for maps.

Field Summary

static boolean

ASSERT Whether assertions are enabled.

Method Summary

void	close() Close the file.
boolean	compact(int fillRate) Try to reduce the file size.
Compressor	getCompressor()
long	getCurrentVersion() Get the current version of the store.
int	getMaxPageSize() The maximum number of key-value pairs in a page.
MVMap<java.lang.String,java.lang.String>	getMetaMap() Get the metadata map.
int	getReadCount() Get the number of read operations since this store was opened.
int	getRetainChunk()
boolean	getReuseSpace()
int	getWriteCount() Get the number of write operations since this store was opened.
boolean	hasUnsavedChanges() Check whether there are any unsaved changes.
long	incrementVersion() Increment the current version.
static MVStore	open(java.lang.String fileName) Open a tree store.
static MVStore	open(java.lang.String fileName, MapFactory mapFactory) Open a tree store.
<K,V> MVMap<K,V>	openMap(java.lang.String name, java.lang.Class<K> keyClass, java.lang.Class<V> valueClass) Open a map.
<T extends MVMap<?,?>> T	openMap(java.lang.String name, java.lang.String mapType, java.lang.String keyType, java.lang.String valueType) Open a map.
void	rollbackTo(long version) Revert to the given version.
void	setCompressor(Compressor compressor)
void	setMaxPageSize(int maxPageSize)
void	setRetainChunk(int retainChunk) Which chunk to retain.
void	setReuseSpace(boolean reuseSpace)
long	store() Commit all changes and persist them to disk.

Methods inherited from class java.lang.Object

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

Field Detail

ASSERT

public static final boolean ASSERT

Whether assertions are enabled.

See Also:

Constant Field Values

Method Detail

open

public static MVStore open(java.lang.String fileName)

Open a tree store.

Parameters:

fileName - the file name

Returns:

the store

open

public static MVStore open(java.lang.String fileName,
                           MapFactory mapFactory)

Open a tree store.

Parameters:

fileName - the file name (null for in-memory)

mapFactory - the map factory

Returns:

the store

openMap

public <T extends MVMap<?,?>> T openMap(java.lang.String name,
                                        java.lang.String mapType,
                                        java.lang.String keyType,
                                        java.lang.String valueType)

Open a map.

Type Parameters:

T - the map type

Parameters:

name - the name of the map

mapType - the map type

keyType - the key type

valueType - the value type

Returns:

the map

getMetaMap

public MVMap<java.lang.String,java.lang.String> getMetaMap()

Get the metadata map. It contains the following entries:

 map.{name} = {mapId}/{keyType}/{valueType}
 root.{mapId} = {rootPos}
 chunk.{chunkId} = {chunkData}
 

Returns:

the metadata map

openMap

public <K,V> MVMap<K,V> openMap(java.lang.String name,
                                java.lang.Class<K> keyClass,
                                java.lang.Class<V> valueClass)

Open a map.

Type Parameters:

K - the key type

V - the value type

Parameters:

name - the name of the map

keyClass - the key class

valueClass - the value class

Returns:

the map

close

public void close()

Close the file. Uncommitted changes are ignored, and all open maps are closed.

incrementVersion

public long incrementVersion()

Increment the current version.

Returns:

the old version

store

public long store()

Commit all changes and persist them to disk. This method does nothing if there are no unsaved changes, otherwise it stores the data and increments the current version.

Returns:

the version before the commit

hasUnsavedChanges

public boolean hasUnsavedChanges()

Check whether there are any unsaved changes.

Returns:

if there are any changes

compact

public boolean compact(int fillRate)

Try to reduce the file size. Chunks with a low number of live items will be re-written. If the current fill rate is higher than the target fill rate, no optimization is done.

Parameters:

fillRate - the minimum percentage of live entries

Returns:

if anything was written

setMaxPageSize

public void setMaxPageSize(int maxPageSize)

getMaxPageSize

public int getMaxPageSize()

The maximum number of key-value pairs in a page.

Returns:

the maximum number of entries

getCompressor

public Compressor getCompressor()

setCompressor

public void setCompressor(Compressor compressor)

getReuseSpace

public boolean getReuseSpace()

setReuseSpace

public void setReuseSpace(boolean reuseSpace)

getRetainChunk

public int getRetainChunk()

setRetainChunk

public void setRetainChunk(int retainChunk)

Which chunk to retain. If not set, old chunks are re-used as soon as possible, which may make it impossible to roll back beyond a save operation, or read a older version before.

This setting is not persisted.

Parameters:

retainChunk - the earliest chunk to retain (0 to retain all chunks, -1 to re-use space as early as possible)

rollbackTo

public void rollbackTo(long version)

Revert to the given version. All later changes (stored or not) are forgotten. All maps that were created later are closed. A rollback to a version before the last stored version is immediately persisted. Before this method returns, the current version is incremented.

Parameters:

version - the version to revert to

getCurrentVersion

public long getCurrentVersion()

Get the current version of the store. When a new store is created, the version is 1. For each commit, it is incremented by one.

Returns:

the version

getWriteCount

public int getWriteCount()

Get the number of write operations since this store was opened.

Returns:

the number of write operations

getReadCount

public int getReadCount()

Get the number of read operations since this store was opened.

Returns:

the number of read operations