Class LogAccessFile
- java.lang.Object
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- org.apache.derby.impl.store.raw.log.LogAccessFile
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public class LogAccessFile extends java.lang.Object
Wraps a RandomAccessFile file to provide buffering on log writes. Only supports the write calls required for the log! MT - unsafe. Caller of this class must provide synchronization. The one exception is with the log file access, LogAccessFile will touch the log only inside synchronized block protected by the semaphore, which is defined by the creator of this object. Write to the log buffers are allowed when there are free buffers even when dirty buffers are being written(flushed) to the disk by a different thread. Only one flush writes to log file at a time, other wait for it to finish. Except for flushLogAccessFile , SyncAccessLogFile other function callers must provide syncronization that will allow only one of them to write to the buffers. Log Buffers are used in circular fashion, each buffer moves through following stages: freeBuffers --> dirtyBuffers --> freeBuffers. Movement of buffers from one stage to another stage is synchronized using the object(this) of this class. A Checksum log record that has the checksum value for the data that is being written to the disk is generated and written before the actual data. Except for the large log records that does not fit into a single buffer, checksum is calcualted for a group of log records that are in the buffer when buffers is switched. Checksum log record is written into the reserved space in the beginning buffer. In case of a large log record that does not fit into a buffer, the checksum is written to the byte[] allocated for the big log record. Checksum log records helps in identifying the incomplete log disk writes during recovery. This is done by recalculating the checksum value for the data on the disk and comparing it to the the value stored in the checksum log record.
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Field Summary
Fields Modifier and Type Field Description private long
checksumInstant
private int
checksumLength
private ChecksumOperation
checksumLogOperation
private LogRecord
checksumLogRecord
private int
checksumLogRecordSize
private LogAccessFileBuffer
currentBuffer
private boolean
databaseEncrypted
private java.util.LinkedList<LogAccessFileBuffer>
dirtyBuffers
private boolean
flushInProgress
private java.util.LinkedList<LogAccessFileBuffer>
freeBuffers
(package private) boolean
inReplicationMasterMode
(package private) boolean
inReplicationSlaveMode
private StorageRandomAccessFile
log
private static int
LOG_NUMBER_LOG_BUFFERS
private static int
LOG_RECORD_FIXED_OVERHEAD_SIZE
The fixed size of a log record is 16 bytes: int length : 4 bytes long instant : 8 bytes int trailing length : 4 bytesprivate static int
LOG_RECORD_HEADER_SIZE
private static int
LOG_RECORD_TRAILER_SIZE
private LogToFile
logFactory
private java.lang.Object
logFileSemaphore
private FormatIdOutputStream
logicalOut
private ArrayOutputStream
logOutputBuffer
(package private) MasterFactory
masterFac
(package private) static int
mon_numBytesToLog
(package private) static int
mon_numWritesToLog
private boolean
writeChecksum
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Constructor Summary
Constructors Constructor Description LogAccessFile(LogToFile logFactory, StorageRandomAccessFile log, int bufferSize)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description private int
appendLogRecordToBuffer(byte[] buff, int pos, int length, long instant, byte[] data, int data_offset, byte[] optional_data, int optional_data_offset, int optional_data_length)
Append a log record to a byte[].void
close()
void
corrupt()
The database is being marked corrupted, get rid of file pointer without writing out anything more.protected void
flushDirtyBuffers()
Write data from all dirty buffers into the log file.void
flushLogAccessFile()
int
getChecksumLogRecordSize()
Return the length of a checksum recordprotected long
reserveSpaceForChecksum(int length, long logFileNumber, long currentPosition)
reserve the space for the checksum log record in the log file.protected void
setReplicationMasterRole(MasterFactory masterFac)
Make this LogAccessFile pass chunks of log records (byte[]) to the MasterFactory when the chunks are written to disk.protected void
setReplicationSlaveRole()
Method to put this LogAccessFile object in replication slave mode, effectively disabling checksum writes.protected void
stopReplicationMasterRole()
Stop this LogAccessFile from passing chunks of log records to the MasterFactory.void
switchLogBuffer()
Appends the current Buffer to the dirty Buffer list and assigns a free buffer to be the currrent active buffer .void
syncLogAccessFile()
Guarantee all writes up to the last call to flushLogAccessFile on disk.void
write(byte[] b, int off, int len)
void
write(int b)
private void
writeChecksumLogRecord(byte[] buffer)
Generate the checkum log record and write it into the log buffer.protected void
writeEndMarker(int marker)
void
writeInt(int i)
private int
writeInt(int i, byte[] b, int p)
void
writeLogRecord(int length, long instant, byte[] data, int data_offset, byte[] optional_data, int optional_data_offset, int optional_data_length)
Write a single log record to the stream.void
writeLong(long l)
private int
writeLong(long l, byte[] b, int p)
private void
writeToLog(byte[] b, int off, int len, long highestInstant)
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Field Detail
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LOG_RECORD_FIXED_OVERHEAD_SIZE
private static final int LOG_RECORD_FIXED_OVERHEAD_SIZE
The fixed size of a log record is 16 bytes: int length : 4 bytes long instant : 8 bytes int trailing length : 4 bytes- See Also:
- Constant Field Values
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LOG_RECORD_HEADER_SIZE
private static final int LOG_RECORD_HEADER_SIZE
- See Also:
- Constant Field Values
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LOG_RECORD_TRAILER_SIZE
private static final int LOG_RECORD_TRAILER_SIZE
- See Also:
- Constant Field Values
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LOG_NUMBER_LOG_BUFFERS
private static final int LOG_NUMBER_LOG_BUFFERS
- See Also:
- Constant Field Values
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freeBuffers
private java.util.LinkedList<LogAccessFileBuffer> freeBuffers
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dirtyBuffers
private java.util.LinkedList<LogAccessFileBuffer> dirtyBuffers
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currentBuffer
private LogAccessFileBuffer currentBuffer
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flushInProgress
private boolean flushInProgress
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log
private final StorageRandomAccessFile log
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logFileSemaphore
private final java.lang.Object logFileSemaphore
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mon_numWritesToLog
static int mon_numWritesToLog
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mon_numBytesToLog
static int mon_numBytesToLog
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masterFac
MasterFactory masterFac
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inReplicationMasterMode
boolean inReplicationMasterMode
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inReplicationSlaveMode
boolean inReplicationSlaveMode
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logOutputBuffer
private ArrayOutputStream logOutputBuffer
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logicalOut
private FormatIdOutputStream logicalOut
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checksumInstant
private long checksumInstant
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checksumLength
private int checksumLength
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checksumLogRecordSize
private int checksumLogRecordSize
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writeChecksum
private boolean writeChecksum
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checksumLogOperation
private ChecksumOperation checksumLogOperation
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checksumLogRecord
private LogRecord checksumLogRecord
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logFactory
private LogToFile logFactory
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databaseEncrypted
private boolean databaseEncrypted
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Constructor Detail
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LogAccessFile
public LogAccessFile(LogToFile logFactory, StorageRandomAccessFile log, int bufferSize)
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Method Detail
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writeLogRecord
public void writeLogRecord(int length, long instant, byte[] data, int data_offset, byte[] optional_data, int optional_data_offset, int optional_data_length) throws StandardException, java.io.IOException
Write a single log record to the stream.For performance pass all parameters rather into a specialized routine rather than maintaining the writeInt, writeLong, and write interfaces that this class provides as a standard OutputStream. It will make it harder to use other OutputStream implementations, but makes for less function calls and allows optimizations knowing when to switch buffers.
This routine handles all log records which are smaller than one log buffer. If a log record is bigger than a log buffer it calls writeUnbufferedLogRecord().
The log record written will always look the same as if the following code had been executed: writeInt(length) writeLong(instant) write(data, data_offset, (length - optional_data_length) ) if (optional_data_length != 0) write(optional_data, optional_data_offset, optional_data_length) writeInt(length)
- Parameters:
length
- (data + optional_data) length bytes to writeinstant
- the log address of this log record.data
- "from" array to copy "data" portion of recdata_offset
- offset in "data" to start copying from.optional_data
- "from" array to copy "optional data" fromoptional_data_offset
- offset in "optional_data" to start copy fromoptional_data_length
- length of optional data to copy.- Throws:
StandardException
- Standard exception policy.java.io.IOException
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appendLogRecordToBuffer
private int appendLogRecordToBuffer(byte[] buff, int pos, int length, long instant, byte[] data, int data_offset, byte[] optional_data, int optional_data_offset, int optional_data_length)
Append a log record to a byte[]. Typically, the byte[] will be currentBuffer, but if a log record that is too big to fit in a buffer is added, buff will be a newly allocated byte[].- Parameters:
buff
- The byte[] the log record is appended topos
- The position in buff where the method will start to append tolength
- (data + optional_data) length bytes to writeinstant
- the log address of this log record.data
- "from" array to copy "data" portion of recdata_offset
- offset in "data" to start copying from.optional_data
- "from" array to copy "optional data" fromoptional_data_offset
- offset in "optional_data" to start copy fromoptional_data_length
- length of optional data to copy.- See Also:
writeLogRecord(int, long, byte[], int, byte[], int, int)
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writeInt
private final int writeInt(int i, byte[] b, int p)
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writeLong
private final int writeLong(long l, byte[] b, int p)
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writeInt
public void writeInt(int i)
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writeLong
public void writeLong(long l)
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write
public void write(int b)
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write
public void write(byte[] b, int off, int len)
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flushDirtyBuffers
protected void flushDirtyBuffers() throws java.io.IOException
Write data from all dirty buffers into the log file.A call for clients of LogAccessFile to insure that all privately buffered data has been writen to the file - so that reads on the file using one of the various scan classes will see all the data which has been writen to this point.
Note that this routine only "writes" the data to the file, this does not mean that the data has been synced to disk unless file was opened in WRITE SYNC mode(rws/rwd). The only way to insure that is by calling is to call syncLogAccessFile() after this call in Non-WRITE sync mode(rw)
MT-Safe : parallel thereads can call this function, only one threads does the flush and the other threads waits for the one that is doing the flush to finish. Currently there are two possible threads that can call this function in parallel 1) A Thread that is doing the commit 2) A Thread that is writing to the log and log buffers are full or a log records does not fit in a buffer. (Log Buffers full(switchLogBuffer() or a log record size that is greater than logbuffer size has to be writtern through writeToLog call directlty) Note: writeToLog() is not synchronized on the semaphore that is used to do buffer management to allow writes to the free buffers when flush is in progress.
- Throws:
java.io.IOException
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flushLogAccessFile
public void flushLogAccessFile() throws java.io.IOException, StandardException
- Throws:
java.io.IOException
StandardException
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switchLogBuffer
public void switchLogBuffer() throws java.io.IOException, StandardException
Appends the current Buffer to the dirty Buffer list and assigns a free buffer to be the currrent active buffer . Flushing of the buffer to disk is delayed if there is a free buffer available. dirty buffers will be flushed to the disk when flushDirtyBuffers() is invoked by a commit call or when no more free buffers are available.- Throws:
java.io.IOException
StandardException
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syncLogAccessFile
public void syncLogAccessFile() throws java.io.IOException, StandardException
Guarantee all writes up to the last call to flushLogAccessFile on disk.A call for clients of LogAccessFile to insure that all data written up to the last call to flushLogAccessFile() are written to disk. This call will not return until those writes have hit disk.
Note that this routine may block waiting for I/O to complete so callers should limit the number of resource held locked while this operation is called. It is expected that the caller Note that this routine only "writes" the data to the file, this does not mean that the data has been synced to disk. The only way to insure that is to first call switchLogBuffer() and then follow by a call of sync().
- Throws:
java.io.IOException
StandardException
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corrupt
public void corrupt() throws java.io.IOException
The database is being marked corrupted, get rid of file pointer without writing out anything more.- Throws:
java.io.IOException
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close
public void close() throws java.io.IOException, StandardException
- Throws:
java.io.IOException
StandardException
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setReplicationMasterRole
protected void setReplicationMasterRole(MasterFactory masterFac)
Make this LogAccessFile pass chunks of log records (byte[]) to the MasterFactory when the chunks are written to disk.- Parameters:
masterFac
- The MasterFactory service responsible for controlling the master side replication behaviour.
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stopReplicationMasterRole
protected void stopReplicationMasterRole()
Stop this LogAccessFile from passing chunks of log records to the MasterFactory.
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setReplicationSlaveRole
protected void setReplicationSlaveRole()
Method to put this LogAccessFile object in replication slave mode, effectively disabling checksum writes. Because checksums are received from the replication master, the slave can not be allowed to add it's own checksums - that would invalidate the checksums and would stop the database from recovering. Replication slave mode must therefore be set before LogAccessFile decides whether to write it's own checksums, and this method is therefore indirectly called from the constructor of this class by calling LogFactory.checkForReplication If replication slave mode for the database is stopped after this object has been created, checksums cannot be reenabled without creating a new instance of this class. That is conveniently handled as LogToFile.recover completes (which automatically happens once replication slave mode is no longer active)
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writeToLog
private void writeToLog(byte[] b, int off, int len, long highestInstant) throws java.io.IOException
- Throws:
java.io.IOException
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reserveSpaceForChecksum
protected long reserveSpaceForChecksum(int length, long logFileNumber, long currentPosition) throws StandardException, java.io.IOException
reserve the space for the checksum log record in the log file.- Parameters:
length
- the length of the log record to be writtenlogFileNumber
- current log file numbercurrentPosition
- current position in the log file.- Returns:
- the space that is needed to write a checksum log record.
- Throws:
StandardException
java.io.IOException
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writeChecksumLogRecord
private void writeChecksumLogRecord(byte[] buffer) throws java.io.IOException, StandardException
Generate the checkum log record and write it into the log buffer. The checksum applies to all bytes from this checksum log record to the next one.- Parameters:
buffer
- The byte[] the checksum is written to. The checksum is always written at the beginning of buffer.- Throws:
java.io.IOException
StandardException
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getChecksumLogRecordSize
public int getChecksumLogRecordSize()
Return the length of a checksum record
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writeEndMarker
protected void writeEndMarker(int marker) throws java.io.IOException, StandardException
- Throws:
java.io.IOException
StandardException
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