com.bigdata.ha.halog

Class HALogReader

java.lang.Object

com.bigdata.ha.halog.HALogReader

All Implemented Interfaces:

IHALogReader

public class HALogReader
extends Object
implements IHALogReader

Given an HALog file can be used to replay the file and can provide a readable dump of the content. When replaying, the current position is compared to the EOF to determine whether more data can be read. The called should call IHALogReader.hasMoreBuffers() and if so read the next associated buffer and process with the returned IHAMessage. If IHALogReader.hasMoreBuffers() is false, then the committing IRootBlockView should be used to commit the replayed transaction.

Author:

Martyn Cutcher

Field Summary

Fields inherited from interface com.bigdata.ha.halog.IHALogReader

HA_LOG_EXT, HALOG_FILTER

Constructor Summary

Constructors

Constructor and Description
HALogReader(File file) CAUTION: This constructor should not be used in circumstances in which the HALogWriter is active since this constructor can not differentiate atomically between the live HALog and a historical HALog and will always provide a read-only view, even if the live HALog file is opened.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes the reader iff it is open.
void	computeDigest(MessageDigest digest) Compute the 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.
boolean	hasMoreBuffers() Checks whether we have reached the end of the file (blocking).
boolean	isEmpty() Return true if the root blocks in the log file have the same commit counter.
boolean	isLive() Return true iff this is was the live HALog at the moment when it was opened (if true, then this flag will remain true even if the writer moves onto another HALog file).
boolean	isOpen() Return true iff the reader is open.
static void	main(String[] args) Utility program will dump log files (or directories containing log files) provided as arguments.
IHAWriteMessage	processNextBuffer(ByteBuffer clientBuffer) Attempts to read the next IHAWriteMessage and then the expected buffer, that is read into the client buffer.
static IHAWriteMessage	processNextBuffer(RandomAccessFile raf, IReopenChannel<FileChannel> reopener, StoreTypeEnum storeType, ByteBuffer clientBuffer)

Methods inherited from class java.lang.Object

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

Constructor Detail

HALogReader

public HALogReader(File file)
            throws IOException

CAUTION: This constructor should not be used in circumstances in which the HALogWriter is active since this constructor can not differentiate atomically between the live HALog and a historical HALog and will always provide a read-only view, even if the live HALog file is opened.

Parameters:

file - The HALog file.

Throws:

IOException

Method Detail

close

public void close()

Description copied from interface: IHALogReader

Closes the reader iff it is open.

Note: Closing a reader does not have a side-effect on any open reader or writer for the same file. Specifically, if two readers are open for the same file and one is closed, then other will remain open. Likewise, if a reader is open for the live HALog file, closing the writer will not close the reader and closing the reader will not close the writer.

Specified by:

close in interface IHALogReader

isOpen

public boolean isOpen()

Description copied from interface: IHALogReader

Return true iff the reader is open.

Specified by:

isOpen in interface IHALogReader

isLive

public boolean isLive()

Description copied from interface: IHALogReader

Return true iff this is was the live HALog at the moment when it was opened (if true, then this flag will remain true even if the writer moves onto another HALog file).

Specified by:

isLive in interface IHALogReader

isEmpty

public boolean isEmpty()

Description copied from interface: IHALogReader

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. FIXME The code disagress and will report [false] if the live log has the same root blocks but has not yet been closed.

Specified by:

isEmpty in interface IHALogReader

getOpeningRootBlock

public IRootBlockView getOpeningRootBlock()

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

Specified by:

getOpeningRootBlock in interface IHALogReader

getClosingRootBlock

public IRootBlockView getClosingRootBlock()

Description copied from interface: IHALogReader

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

Specified by:

getClosingRootBlock in interface IHALogReader

hasMoreBuffers

public boolean hasMoreBuffers()
                       throws IOException

Description copied from interface: IHALogReader

Checks whether we have reached the end of the file (blocking).

Note: This method will block if this is the live HALog. This allows a process to block until the next message is made available on the live HALog by the writer.

Note: This method is non-blocking if this is not the live HALog since the decision can be made deterministically by inspecting the #of messages available (in the closing root block) and the #of messages consumed by the reader.

Specified by:

hasMoreBuffers in interface IHALogReader

Returns:

Return false if (a) the file is closed on entry to this method; (b) the live HALog is closed while waiting for more data to become available; or (c) the end of a historical HALog file has been reached. Return true iff more data can be read from the file.

Throws:

IOException - if there is an error reading from the backing file.

processNextBuffer

public IHAWriteMessage processNextBuffer(ByteBuffer clientBuffer)
                                  throws IOException

Description copied from interface: IHALogReader

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.

Specified by:

processNextBuffer in interface IHALogReader

Parameters:

clientBuffer - A buffer from the DirectBufferPool.INSTANCE.

Throws:

IOException

processNextBuffer

public static IHAWriteMessage processNextBuffer(RandomAccessFile raf,
                                IReopenChannel<FileChannel> reopener,
                                StoreTypeEnum storeType,
                                ByteBuffer clientBuffer)
                                         throws IOException

Throws:

IOException

main

public static void main(String[] args)
                 throws InterruptedException

Utility program will dump log files (or directories containing log files) provided as arguments.

Parameters:

args - Zero or more files or directories.

Throws:

IOException

InterruptedException

computeDigest

public void computeDigest(MessageDigest digest)
                   throws DigestException,
                          IOException

Description copied from interface: IHALogReader

Compute the digest. If the IHALogReader is backed by the live HALog, then only the digest of the then current extent will be computed.

Specified by:

computeDigest in interface IHALogReader

Throws:

DigestException

IOException