com.bigdata.ha.althalog

Interface IHALogReader

public interface IHALogReader

Interface for reading on an HA Log. Readers can be requested of any HALogFile.

Field Summary

Fields

Modifier and Type	Field and Description
static String	HA_LOG_EXT The filename extension used for the HALog files.
static FileFilter	HALOG_FILTER A FileFilter that visits all files ending with the HA_LOG_EXT and the names of all direct child directories.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes the Reader.
void	computeDigest(MessageDigest digest)
IRootBlockView	getClosingRootBlock() The IRootBlockView for the committed state AFTER the write set contained in the HA log file has been applied.
IRootBlockView	getOpeningRootBlock() The IRootBlockView for the committed state BEFORE the write set contained in the HA log file has been applied.
boolean	hasMoreBuffers() Checks whether we have reached the end of the file.
boolean	isEmpty() Return true if the root blocks in the log file have the same commit counter.
IHAWriteMessage	processNextBuffer(ByteBuffer clientBuffer) Attempts to read the next IHAWriteMessage and then the expected buffer, that is read into the client buffer.

Field Detail

HA_LOG_EXT

static final String HA_LOG_EXT

The filename extension used for the HALog files.

See Also:

Constant Field Values

HALOG_FILTER

static final FileFilter HALOG_FILTER

A FileFilter that visits all files ending with the HA_LOG_EXT and the names of all direct child directories. This FileFilter may be used to establish recursive scans of the HALog directory.

Method Detail

close

void close()
           throws IOException

Closes the Reader.

Throws:

IOException

isEmpty

boolean isEmpty()

Return true if the root blocks in the log file have the same commit counter. Such log files are logically empty regardless of their length.

getOpeningRootBlock

IRootBlockView getOpeningRootBlock()

The IRootBlockView for the committed state BEFORE the write set contained in the HA log file has been applied.

getClosingRootBlock

IRootBlockView getClosingRootBlock()
                                   throws IOException

The IRootBlockView for the committed state AFTER the write set contained in the HA log file has been applied.

Throws:

IOException

hasMoreBuffers

boolean hasMoreBuffers()
                       throws IOException

Checks whether we have reached the end of the file.

Throws:

IOException

processNextBuffer

IHAWriteMessage processNextBuffer(ByteBuffer clientBuffer)
                                  throws IOException

Attempts to read the next IHAWriteMessage and then the expected buffer, that is read into the client buffer. The IHAWriteMessage is returned to the caller.

Note: The caller's buffer will be filled in IFF the data is on the HALog. For some IHABufferStrategy implementations, that data is not present in the HALog. The caller's buffer will not be modified and the caller is responsible for getting the data from the IHABufferStrategy (e.g., for the WORMStrategy).

Note: IF the buffer is filled, then the limit will be the #of bytes ready to be transmitted and the position will be zero.

Parameters:

clientBuffer - A buffer from the DirectBufferPool.INSTANCE.

Throws:

IOException

computeDigest

void computeDigest(MessageDigest digest)
                   throws DigestException,
                          IOException

Throws:

DigestException

IOException