org.apache.jackrabbit.mk.blobs

Class AbstractBlobStore

java.lang.Object

org.apache.jackrabbit.mk.blobs.AbstractBlobStore

All Implemented Interfaces:

BlobStore, Cache.Backend<AbstractBlobStore.BlockId,AbstractBlobStore.Data>

Direct Known Subclasses:

DbBlobStore, FileBlobStore, MemoryBlobStore

public abstract class AbstractBlobStore
extends Object
implements BlobStore, Cache.Backend<AbstractBlobStore.BlockId,AbstractBlobStore.Data>

An abstract data store that splits the binaries in relatively small blocks, so that each block fits in memory.

Each data store id is a list of zero or more entries. Each entry is either

• data (a number of bytes), or
• the hash code of the content of a number of bytes, or
• the hash code of the content of a data store id (indirect hash)

Thanks to the indirection, blocks can be kept relatively small, so that caching is simpler, and so that the storage backend doesn't need to support arbitrary size blobs (some storage backends buffer blobs in memory) and fast seeks (some storage backends re-read the whole blob when seeking).

The the format of a 'data' entry is: type (one byte; 0 for data), length (variable size int), data (bytes).

The format of a 'hash of content' entry is: type (one byte; 1 for hash), level (variable size int, 0 meaning not nested), size (variable size long), hash code length (variable size int), hash code.

The format of a 'hash of data store id' entry is: type (one byte; 1 for hash), level (variable size int, nesting level), total size (variable size long), size of data store id (variable size long), hash code length (variable size int), hash code.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AbstractBlobStore.BlockId A block id.
static class	AbstractBlobStore.Data The data for a block.

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	BLOCK_SIZE_LIMIT
protected static String	HASH_ALGORITHM
protected Map<String,WeakReference<String>>	inUse
protected static int	TYPE_DATA
protected static int	TYPE_HASH
protected static int	TYPE_HASH_COMPRESSED

Constructor Summary

Constructors

Constructor and Description
AbstractBlobStore()

Method Summary

Methods

Modifier and Type	Method and Description
void	clearCache()
void	clearInUse()
long	getBlobLength(String blobId) Get the length of the blob.
int	getBlockSize()
long	getBlockSizeMin()
protected abstract boolean	isMarkEnabled()
AbstractBlobStore.Data	load(AbstractBlobStore.BlockId id) Load the object.
protected abstract void	mark(AbstractBlobStore.BlockId id)
protected void	mark(String blobId)
protected void	markInUse()
int	readBlob(String blobId, long pos, byte[] buff, int off, int length) Read a number of bytes from a blob.
protected abstract byte[]	readBlockFromBackend(AbstractBlobStore.BlockId id) Load the block from the storage backend.
void	setBlockSize(int x)
void	setBlockSizeMin(int x)
abstract void	startMark()
protected abstract void	storeBlock(byte[] digest, int level, byte[] data) Store a block of data.
abstract int	sweep()
protected void	usesBlobId(String blobId)
String	writeBlob(InputStream in) Write a blob from an input stream.
String	writeBlob(String tempFilePath) Write a blob from a temporary file.

Methods inherited from class java.lang.Object

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

Field Detail

HASH_ALGORITHM

protected static final String HASH_ALGORITHM

See Also:

Constant Field Values

TYPE_DATA

protected static final int TYPE_DATA

See Also:

Constant Field Values

TYPE_HASH

protected static final int TYPE_HASH

See Also:

Constant Field Values

TYPE_HASH_COMPRESSED

protected static final int TYPE_HASH_COMPRESSED

See Also:

Constant Field Values

BLOCK_SIZE_LIMIT

protected static final int BLOCK_SIZE_LIMIT

See Also:

Constant Field Values

inUse

protected Map<String,WeakReference<String>> inUse

Constructor Detail

AbstractBlobStore

public AbstractBlobStore()

Method Detail

setBlockSizeMin

public void setBlockSizeMin(int x)

getBlockSizeMin

public long getBlockSizeMin()

setBlockSize

public void setBlockSize(int x)

getBlockSize

public int getBlockSize()

writeBlob

public String writeBlob(String tempFilePath)
                 throws Exception

Write a blob from a temporary file. The temporary file is removed afterwards. A file based blob stores might simply rename the file, so that no additional writes are necessary.

Parameters:

tempFilePath - the temporary file

Returns:

the blob id

Throws:

Exception

writeBlob

public String writeBlob(InputStream in)
                 throws Exception

Description copied from interface: BlobStore

Write a blob from an input stream. This method closes the input stream.

Specified by:

writeBlob in interface BlobStore

Parameters:

in - the input stream

Returns:

the blob id

Throws:

Exception

usesBlobId

protected void usesBlobId(String blobId)

clearInUse

public void clearInUse()

clearCache

public void clearCache()

storeBlock

protected abstract void storeBlock(byte[] digest,
              int level,
              byte[] data)
                            throws Exception

Store a block of data.

Parameters:

digest - the content hash

level - the indirection level (0 is for user data, 1 is a list of digests that point to user data, 2 is a list of digests that point to digests, and so on). This parameter is for informational use only, and it is not required to store it unless that's easy to achieve

data - the data to be stored

Throws:

Exception

startMark

public abstract void startMark()
                        throws Exception

Throws:

Exception

sweep

public abstract int sweep()
                   throws Exception

Throws:

Exception

isMarkEnabled

protected abstract boolean isMarkEnabled()

mark

protected abstract void mark(AbstractBlobStore.BlockId id)
                      throws Exception

Throws:

Exception

markInUse

protected void markInUse()
                  throws Exception

Throws:

Exception

readBlob

public int readBlob(String blobId,
           long pos,
           byte[] buff,
           int off,
           int length)
             throws Exception

Description copied from interface: BlobStore

Read a number of bytes from a blob.

Specified by:

readBlob in interface BlobStore

Parameters:

blobId - the blob id

pos - the position within the blob

buff - the target byte array

off - the offset within the target array

length - the number of bytes to read

Returns:

the number of bytes read

Throws:

Exception

load

public AbstractBlobStore.Data load(AbstractBlobStore.BlockId id)

Description copied from interface: Cache.Backend

Load the object. The method does not need to be synchronized (it is synchronized in the cache)

Specified by:

load in interface Cache.Backend<AbstractBlobStore.BlockId,AbstractBlobStore.Data>

Parameters:

id - the key

Returns:

the value

readBlockFromBackend

protected abstract byte[] readBlockFromBackend(AbstractBlobStore.BlockId id)
                                        throws Exception

Load the block from the storage backend. Returns null if the block was not found.

Parameters:

id - the block id

Returns:

the block data, or null

Throws:

Exception

getBlobLength

public long getBlobLength(String blobId)
                   throws IOException

Description copied from interface: BlobStore

Get the length of the blob.

Specified by:

getBlobLength in interface BlobStore

Parameters:

blobId - the blob id

Returns:

the length

Throws:

IOException

mark

protected void mark(String blobId)
             throws IOException

Throws:

IOException