Package org.dizitart.no2.mvstore.compat.v1.mvstore

Class MVStore

    • Method Detail

      • open

        public static MVStore open​(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​(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​(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 Set<String> getMapNames()
        Get the set of all map names.
        Returns:
        the set of names

      • getMetaMap

        public MVMap<String,​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​(String name)
        Check whether a given map exists.
        Parameters:
        name - the map name
        Returns:
        true if it exists

      • hasData

        public boolean hasData​(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 AutoCloseable

      • close

        public void close​(long allowedCompactionTime)
        Close the file and the store. Unsaved changes are written to disk first, and compaction (up to a specified number of milliseconds) is attempted.
        Parameters:
        allowedCompactionTime - the allowed time for compaction (in milliseconds)

      • 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

      • compactMoveChunks

        public void compactMoveChunks()
        Compact by moving all chunks next to each other.

      • sync

        public void sync()
        Force all stored changes to be written to the storage. The default implementation calls FileChannel.force(true).

      • compactFile

        public void compactFile​(long maxCompactTime)
        Compact store file, that is, compact blocks that have a low fill rate, and move chunks next to each other. This will typically shrink the file. Changes are flushed to the file, and old chunks are overwritten.
        Parameters:
        maxCompactTime - the maximum time in milliseconds to compact

      • 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

      • getChunksFillRate

        public int getChunksFillRate()
        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)

      • getFillRate

        public int getFillRate()

      • 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

      • registerUnsavedMemory

        public void registerUnsavedMemory​(int memory)
        Adjust amount of "unsaved memory" meaning amount of RAM occupied by pages not saved yet to the file. This is the amount which triggers auto-commit.
        Parameters:
        memory - adjustment

      • 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

      • getFileStore

        public FileStore getFileStore()
        Get the file store.
        Returns:
        the file store

      • getStoreHeader

        public Map<String,​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,
                      String newName)
        Rename a map.
        Parameters:
        map - the map
        newName - the new name

      • removeMap

        public void removeMap​(MVMap<?,​?> map)
        Remove a map from the current version of the store.
        Parameters:
        map - the map to remove

      • removeMap

        public void removeMap​(String name)
        Remove map by name.
        Parameters:
        name - the map name

      • getMapName

        public 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

      • isBackgroundThread

        public boolean isBackgroundThread()

      • 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

      • isReadOnly

        public boolean isReadOnly()
        Whether the store is read-only.
        Returns:
        true if it is

      • getCacheHitRatio

        public int getCacheHitRatio()

      • 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()