Package com.orientechnologies.orient.core.storage.cache.local.doublewritelog

Interface DoubleWriteLog

All Known Implementing Classes:

DoubleWriteLogGL, DoubleWriteLogNoOP

public interface DoubleWriteLog

Interface for the log which keeps data of pages before they will be finally fsync-ed to the data files. This log is used to implement double write pattern.

At the first step we perform fsync of the data to the log using single sequential write calling write(ByteBuffer[], int[], int[]) method.

As the second step we write pages to the data files.

At third step we fsync data files in background process and then truncate log calling truncate() method. Write to the file and truncation of data should be done in single lock to prevent situation when data are written to the log but not to the pages and then truncated. That is typically not a problem because write cache uses single thread model.

If during the write of pages we reach log threshold write(ByteBuffer[], int[], int[]) method will return true. If that happens fsync of pages should be called to truncate page log.

Method Summary

Modifier and Type	Method	Description
void	close()
void	endCheckpoint()
OPointer	loadPage(int fileId, int pageIndex, OByteBufferPool bufferPool)
void	open(String storageName, Path storagePath, int pageSize)
void	restoreModeOff()
void	restoreModeOn()
void	startCheckpoint()
void	truncate()
boolean	write(ByteBuffer[] buffers, int[] fileId, int[] pageIndex)

Method Details

write

boolean write(ByteBuffer[] buffers,
 int[] fileId,
 int[] pageIndex)
       throws IOException

Throws:

IOException

truncate

void truncate()
       throws IOException

Throws:

IOException

open

void open(String storageName,
 Path storagePath,
 int pageSize)
   throws IOException

Throws:

IOException

loadPage

OPointer loadPage(int fileId,
 int pageIndex,
 OByteBufferPool bufferPool)
           throws IOException

Throws:

IOException

restoreModeOn

void restoreModeOn()
            throws IOException

Throws:

IOException

restoreModeOff

void restoreModeOff()

close

void close()
    throws IOException

Throws:

IOException

startCheckpoint

void startCheckpoint()
              throws IOException

Throws:

IOException

endCheckpoint

void endCheckpoint()