MVStore

java.lang.Object
- org.h2.mvstore.MVStore

All Implemented Interfaces:: java.lang.AutoCloseable

public class MVStore
extends java.lang.Object
implements java.lang.AutoCloseable

A persistent storage for maps.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static class`	`MVStore.Builder` A builder for an MVStore.
`static class`	`MVStore.TxCounter` Class TxCounter is a simple data structure to hold version of the store along with the counter of open transactions, which are still operating on this version.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`close()` Close the file and the store.
`void`	`closeImmediately()` Close the file and the store, without writing anything.
`long`	`commit()` Commit the changes.
`boolean`	`compact(int targetFillRate, int write)` Try to increase the fill rate by re-writing partially full chunks.
`void`	`compactMoveChunks()` Compact by moving all chunks next to each other.
`void`	`compactMoveChunks(int targetFillRate, long moveSize)` Compact the store by moving all chunks next to each other, if there is free space between chunks.
`boolean`	`compactRewriteFully()` Compact the store by moving all live pages to new chunks.
`void`	`deregisterVersionUsage(MVStore.TxCounter txCounter)` De-register (close) completed operation (transaction).
`int`	`getAutoCommitDelay()` Get the auto-commit delay.
`int`	`getAutoCommitMemory()` Get the maximum memory (in bytes) used for unsaved pages.
`CacheLongKeyLIRS<Page>`	`getCache()` Get the cache.
`int`	`getCacheSize()` Get the maximum cache size, in MB.
`int`	`getCacheSizeUsed()` Get the amount of memory used for caching, in MB.
`int`	`getCurrentFillRate()` Get the current fill rate (percentage of used space in the file).
`long`	`getCurrentVersion()` Get the current version of the data.
`FileStore`	`getFileStore()` Get the file store.
`int`	`getKeysPerPage()`
`long`	`getLastStoredVersion()`
`<K,V> MVMap<K,V>`	`getMap(int id)` Get map by id.
`java.lang.String`	`getMapName(int id)` Get the name of the given map.
`java.util.Set<java.lang.String>`	`getMapNames()` Get the set of all map names.
`long`	`getMaxPageSize()`
`MVMap<java.lang.String,java.lang.String>`	`getMetaMap()` Get the metadata map.
`long`	`getOldestVersionToKeep()` Get the oldest version to retain in memory, which is the manually set retain version, or the current store version (whatever is older).
`int`	`getPageSplitSize()`
`java.lang.IllegalStateException`	`getPanicException()`
`int`	`getRetentionTime()`
`boolean`	`getReuseSpace()`
`java.util.Map<java.lang.String,java.lang.Object>`	`getStoreHeader()` Get the store header.
`int`	`getStoreVersion()` Get the store version.
`int`	`getUnsavedMemory()` Get the estimated memory (in bytes) of unsaved data.
`double`	`getUpdateFailureRatio()`
`long`	`getVersionsToKeep()` Get the oldest version to retain in memory (for in-memory stores).
`boolean`	`hasData(java.lang.String name)` Check whether a given map exists and has data.
`boolean`	`hasMap(java.lang.String name)` Check whether a given map exists.
`boolean`	`hasUnsavedChanges()` Check whether there are any unsaved changes.
`boolean`	`isClosed()` Determine that store is open, or wait for it to be closed (by other thread)
`boolean`	`isReadOnly()` Whether the store is read-only.
`boolean`	`isSaveNeeded()`
`static MVStore`	`open(java.lang.String fileName)` Open a store in exclusive mode.
`<K,V> MVMap<K,V>`	`openMap(java.lang.String name)` Open a map with the default settings.
`<M extends MVMap<K,V>,K,V> M`	`openMap(java.lang.String name, MVMap.MapBuilder<M,K,V> builder)` Open a map with the given builder.
`void`	`registerUnsavedPage(int memory)` Increment the number of unsaved pages.
`MVStore.TxCounter`	`registerVersionUsage()` Register opened operation (transaction).
`void`	`removeMap(MVMap<?,?> map)` Remove a map.
`void`	`removeMap(MVMap<?,?> map, boolean delayed)` Remove a map.
`void`	`removeMap(java.lang.String name)` Remove map by name.
`void`	`renameMap(MVMap<?,?> map, java.lang.String newName)` Rename a map.
`void`	`rollback()` Revert to the beginning of the current version, reverting all uncommitted changes.
`void`	`rollbackTo(long version)` Revert to the beginning of the given version.
`void`	`setAutoCommitDelay(int millis)` Set the maximum delay in milliseconds to auto-commit changes.
`void`	`setCacheSize(int mb)` Set the read cache size in MB.
`void`	`setRetentionTime(int ms)` How long to retain old, persisted chunks, in milliseconds.
`void`	`setReuseSpace(boolean reuseSpace)` Whether empty space in the file should be re-used.
`void`	`setStoreVersion(int version)` Update the store version.
`void`	`setVersionsToKeep(int count)` How many versions to retain for in-memory stores.
`void`	`sync()` Force all stored changes to be written to the storage.
`long`	`tryCommit()` Unlike regular commit this method returns immediately if there is commit in progress on another thread, otherwise it acts as regular commit.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - getPanicException
```
public java.lang.IllegalStateException getPanicException()
```
  - open
```
public static MVStore open(java.lang.String fileName)
```
    Open a store in exclusive mode. For a file-based store, the parent directory must already exist.
    
    Parameters:
    fileName - the file name (null for in-memory)
    
    Returns:
    the store
  - openMap
```
public <K,V> MVMap<K,V> openMap(java.lang.String name)
```
    Open a map with the default settings. The map is automatically create if it does not yet exist. If a map with this name is already open, this map is returned.
    
    Type Parameters:
    K - the key type
    V - the value type
    Parameters:
    name - the name of the map
    
    Returns:
    the map
  - openMap
```
public <M extends MVMap<K,V>,K,V> M openMap(java.lang.String name,
                                   MVMap.MapBuilder<M,K,V> builder)
```
    Open a map with the given builder. The map is automatically create if it does not yet exist. If a map with this name is already open, this map is returned.
    
    Type Parameters:
    M - the map type
    K - the key type
    V - the value type
    Parameters:
    name - the name of the map
    builder - the map builder
    
    Returns:
    the map
  - getMap
```
public <K,V> MVMap<K,V> getMap(int id)
```
    Get map by id.
    
    Type Parameters:
    K - the key type
    V - the value type
    Parameters:
    id - map id
    
    Returns:
    Map
  - getMapNames
```
public java.util.Set<java.lang.String> getMapNames()
```
    Get the set of all map names.
    
    Returns:
    the set of names
  - getMetaMap
```
public MVMap<java.lang.String,java.lang.String> getMetaMap()
```
    Get the metadata map. This data is for informational purposes only. The data is subject to change in future versions.
    The data in this map should not be modified (changing system data may corrupt the store). If modifications are needed, they need be synchronized on the store.
    The metadata map contains the following entries:
```
 chunk.{chunkId} = {chunk metadata}
 name.{name} = {mapId}
 map.{mapId} = {map metadata}
 root.{mapId} = {root position}
 setting.storeVersion = {version}
 
```
    Returns:
    the metadata map
  - hasMap
```
public boolean hasMap(java.lang.String name)
```
    Check whether a given map exists.
    
    Parameters:
    name - the map name
    
    Returns:
    true if it exists
  - hasData
```
public boolean hasData(java.lang.String name)
```
    Check whether a given map exists and has data.
    
    Parameters:
    name - the map name
    
    Returns:
    true if it exists and has data.
  - close
```
public void close()
```
    Close the file and the store. Unsaved changes are written to disk first.
    
    Specified by:
    
    close in interface java.lang.AutoCloseable
  - closeImmediately
```
public void closeImmediately()
```
    Close the file and the store, without writing anything. This will try to stop the background thread (without waiting for it). This method ignores all errors.
  - tryCommit
```
public long tryCommit()
```
    Unlike regular commit this method returns immediately if there is commit in progress on another thread, otherwise it acts as regular commit. This method may return BEFORE this thread changes are actually persisted!
    
    Returns:
    the new version (incremented if there were changes)
  - commit
```
public long commit()
```
    Commit the changes.
    This method does nothing if there are no unsaved changes, otherwise it increments the current version and stores the data (for file based stores).
    It is not necessary to call this method when auto-commit is enabled (the default setting), as in this case it is automatically called from time to time or when enough changes have accumulated. However, it may still be called to flush all changes to disk.
    At most one store operation may run at any time.
    
    Returns:
    the new version (incremented if there were changes)
  - hasUnsavedChanges
```
public boolean hasUnsavedChanges()
```
    Check whether there are any unsaved changes.
    
    Returns:
    if there are any changes
  - compactRewriteFully
```
public boolean compactRewriteFully()
```
    Compact the store by moving all live pages to new chunks.
    
    Returns:
    if anything was written
  - compactMoveChunks
```
public void compactMoveChunks()
```
    Compact by moving all chunks next to each other.
  - compactMoveChunks
```
public void compactMoveChunks(int targetFillRate,
                     long moveSize)
```
    Compact the store by moving all chunks next to each other, if there is free space between chunks. This might temporarily increase the file size. Chunks are overwritten irrespective of the current retention time. Before overwriting chunks and before resizing the file, syncFile() is called.
    
    Parameters:
    targetFillRate - do nothing if the file store fill rate is higher than this
    moveSize - the number of bytes to move
  - sync
```
public void sync()
```
    Force all stored changes to be written to the storage. The default implementation calls FileChannel.force(true).
  - compact
```
public boolean compact(int targetFillRate,
              int write)
```
    Try to increase the fill rate by re-writing partially full chunks. Chunks with a low number of live items are re-written.
    If the current fill rate is higher than the target fill rate, nothing is done.
    Please note this method will not necessarily reduce the file size, as empty chunks are not overwritten.
    Only data of open maps can be moved. For maps that are not open, the old chunk is still referenced. Therefore, it is recommended to open all maps before calling this method.
    
    Parameters:
    targetFillRate - the minimum percentage of live entries
    write - the minimum number of bytes to write
    
    Returns:
    if a chunk was re-written
  - getCurrentFillRate
```
public int getCurrentFillRate()
```
    Get the current fill rate (percentage of used space in the file). Unlike the fill rate of the store, here we only account for chunk data; the fill rate here is how much of the chunk data is live (still referenced). Young chunks are considered live.
    
    Returns:
    the fill rate, in percent (100 is completely full)
  - getPageSplitSize
```
public int getPageSplitSize()
```
  - getKeysPerPage
```
public int getKeysPerPage()
```
  - getMaxPageSize
```
public long getMaxPageSize()
```
  - getReuseSpace
```
public boolean getReuseSpace()
```
  - setReuseSpace
```
public void setReuseSpace(boolean reuseSpace)
```
    Whether empty space in the file should be re-used. If enabled, old data is overwritten (default). If disabled, writes are appended at the end of the file.
    This setting is specially useful for online backup. To create an online backup, disable this setting, then copy the file (starting at the beginning of the file). In this case, concurrent backup and write operations are possible (obviously the backup process needs to be faster than the write operations).
    
    Parameters:
    reuseSpace - the new value
  - getRetentionTime
```
public int getRetentionTime()
```
  - setRetentionTime
```
public void setRetentionTime(int ms)
```
    How long to retain old, persisted chunks, in milliseconds. Chunks that are older may be overwritten once they contain no live data.
    The default value is 45000 (45 seconds) when using the default file store. It is assumed that a file system and hard disk will flush all write buffers within this time. Using a lower value might be dangerous, unless the file system and hard disk flush the buffers earlier. To manually flush the buffers, use MVStore.getFile().force(true), however please note that according to various tests this does not always work as expected depending on the operating system and hardware.
    The retention time needs to be long enough to allow reading old chunks while traversing over the entries of a map.
    This setting is not persisted.
    
    Parameters:
    ms - how many milliseconds to retain old chunks (0 to overwrite them as early as possible)
  - setVersionsToKeep
```
public void setVersionsToKeep(int count)
```
    How many versions to retain for in-memory stores. If not set, 5 old versions are retained.
    
    Parameters:
    count - the number of versions to keep
  - getVersionsToKeep
```
public long getVersionsToKeep()
```
    Get the oldest version to retain in memory (for in-memory stores).
    
    Returns:
    the version
  - getOldestVersionToKeep
```
public long getOldestVersionToKeep()
```
    Get the oldest version to retain in memory, which is the manually set retain version, or the current store version (whatever is older).
    
    Returns:
    the version
  - registerUnsavedPage
```
public void registerUnsavedPage(int memory)
```
    Increment the number of unsaved pages.
    
    Parameters:
    memory - the memory usage of the page
  - isSaveNeeded
```
public boolean isSaveNeeded()
```
  - getStoreVersion
```
public int getStoreVersion()
```
    Get the store version. The store version is usually used to upgrade the structure of the store after upgrading the application. Initially the store version is 0, until it is changed.
    
    Returns:
    the store version
  - setStoreVersion
```
public void setStoreVersion(int version)
```
    Update the store version.
    
    Parameters:
    version - the new store version
  - rollback
```
public void rollback()
```
    Revert to the beginning of the current version, reverting all uncommitted changes.
  - rollbackTo
```
public void rollbackTo(long version)
```
    Revert to the beginning of 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. Rollback to version 0 means all data is removed.
    
    Parameters:
    version - the version to revert to
  - getCurrentVersion
```
public long getCurrentVersion()
```
    Get the current version of the data. When a new store is created, the version is 0.
    
    Returns:
    the version
  - getLastStoredVersion
```
public long getLastStoredVersion()
```
  - getFileStore
```
public FileStore getFileStore()
```
    Get the file store.
    
    Returns:
    the file store
  - getStoreHeader
```
public java.util.Map<java.lang.String,java.lang.Object> getStoreHeader()
```
    Get the store header. This data is for informational purposes only. The data is subject to change in future versions. The data should not be modified (doing so may corrupt the store).
    
    Returns:
    the store header
  - renameMap
```
public void renameMap(MVMap<?,?> map,
             java.lang.String newName)
```
    Rename a map.
    
    Parameters:
    map - the map
    newName - the new name
  - removeMap
```
public void removeMap(MVMap<?,?> map)
```
    Remove a map. Please note rolling back this operation does not restore the data; if you need this ability, use Map.clear().
    
    Parameters:
    map - the map to remove
  - removeMap
```
public void removeMap(MVMap<?,?> map,
             boolean delayed)
```
    Remove a map.
    
    Parameters:
    map - the map to remove
    delayed - whether to delay deleting the metadata
  - removeMap
```
public void removeMap(java.lang.String name)
```
    Remove map by name.
    
    Parameters:
    name - the map name
  - getMapName
```
public java.lang.String getMapName(int id)
```
    Get the name of the given map.
    
    Parameters:
    id - the map id
    
    Returns:
    the name, or null if not found
  - setCacheSize
```
public void setCacheSize(int mb)
```
    Set the read cache size in MB.
    
    Parameters:
    mb - the cache size in MB.
  - isClosed
```
public boolean isClosed()
```
    Determine that store is open, or wait for it to be closed (by other thread)
    
    Returns:
    true if store is open, false otherwise
  - setAutoCommitDelay
```
public void setAutoCommitDelay(int millis)
```
    Set the maximum delay in milliseconds to auto-commit changes.
    To disable auto-commit, set the value to 0. In this case, changes are only committed when explicitly calling commit.
    The default is 1000, meaning all changes are committed after at most one second.
    
    Parameters:
    millis - the maximum delay
  - getAutoCommitDelay
```
public int getAutoCommitDelay()
```
    Get the auto-commit delay.
    
    Returns:
    the delay in milliseconds, or 0 if auto-commit is disabled.
  - getAutoCommitMemory
```
public int getAutoCommitMemory()
```
    Get the maximum memory (in bytes) used for unsaved pages. If this number is exceeded, unsaved changes are stored to disk.
    
    Returns:
    the memory in bytes
  - getUnsavedMemory
```
public int getUnsavedMemory()
```
    Get the estimated memory (in bytes) of unsaved data. If the value exceeds the auto-commit memory, the changes are committed.
    The returned value is an estimation only.
    
    Returns:
    the memory in bytes
  - getCacheSizeUsed
```
public int getCacheSizeUsed()
```
    Get the amount of memory used for caching, in MB. Note that this does not include the page chunk references cache, which is 25% of the size of the page cache.
    
    Returns:
    the amount of memory used for caching
  - getCacheSize
```
public int getCacheSize()
```
    Get the maximum cache size, in MB. Note that this does not include the page chunk references cache, which is 25% of the size of the page cache.
    
    Returns:
    the cache size
  - getCache
```
public CacheLongKeyLIRS<Page> getCache()
```
    Get the cache.
    
    Returns:
    the cache
  - isReadOnly
```
public boolean isReadOnly()
```
    Whether the store is read-only.
    
    Returns:
    true if it is
  - getUpdateFailureRatio
```
public double getUpdateFailureRatio()
```
  - registerVersionUsage
```
public MVStore.TxCounter registerVersionUsage()
```
    Register opened operation (transaction). This would increment usage counter for the current version. This version (and all after it) should not be dropped until all transactions involved are closed and usage counter goes to zero.
    
    Returns:
    TxCounter to be decremented when operation finishes (transaction closed).
  - deregisterVersionUsage
```
public void deregisterVersionUsage(MVStore.TxCounter txCounter)
```
    De-register (close) completed operation (transaction). This will decrement usage counter for the corresponding version. If counter reaches zero, that version (and all unused after it) can be dropped immediately.
    
    Parameters:
    txCounter - to be decremented, obtained from registerVersionUsage()

Class MVStore

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Method Detail

getPanicException

open

openMap

openMap

getMap

getMapNames

getMetaMap

hasMap

hasData

close

closeImmediately

tryCommit

commit

hasUnsavedChanges

compactRewriteFully

compactMoveChunks

compactMoveChunks

sync

compact

getCurrentFillRate

getPageSplitSize

getKeysPerPage

getMaxPageSize

getReuseSpace

setReuseSpace

getRetentionTime

setRetentionTime

setVersionsToKeep

getVersionsToKeep

getOldestVersionToKeep

registerUnsavedPage

isSaveNeeded

getStoreVersion

setStoreVersion

rollback

rollbackTo

getCurrentVersion

getLastStoredVersion

getFileStore

getStoreHeader

renameMap

removeMap

removeMap

removeMap

getMapName

setCacheSize

isClosed

setAutoCommitDelay

getAutoCommitDelay

getAutoCommitMemory

getUnsavedMemory

getCacheSizeUsed

getCacheSize

getCache

isReadOnly

getUpdateFailureRatio

registerVersionUsage

deregisterVersionUsage