com.orientechnologies.orient.core.storage.impl.local.paginated.wal

Interface OLogSegment

All Superinterfaces:

Comparable<OLogSegment>

public interface OLogSegment
extends Comparable<OLogSegment>

Basic interface for classes which present log segments of WAL.

WAL is split by segments. Segments are used to truncate WAL by portions. All transactions which are started inside of segment should not cross segment. So they should be finished before new segment will be started.

Main reason of creation of this interface is support of different binary formats of WAL in the same deployment.

To detect which version of binary format is stored we use value stored under OWALPage.MAGIC_NUMBER_OFFSET

Method Summary

Modifier and Type	Method and Description
OLogSequenceNumber	begin()
void	close(boolean flush) Writes buffer of the segment to the disk and closes all acquired resources.
void	delete() Clears the buffer and deletes file content.
OLogSequenceNumber	end()
long	filledUpTo()
void	flush() Writes buffer of the segment to the disk and performs fsync of data.
OLogSequenceNumber	getNextLSN(OLogSequenceNumber lsn) Returns LSN of the record which follows after the record with passed in LSN.
long	getOrder()
String	getPath()
void	init() This method should be called before segment started to be used by WAL.
OLogSequenceNumber	logRecord(byte[] record) Appends new records to the WAL segment and returns LSN of it.
byte[]	readRecord(OLogSequenceNumber lsn) Reads WAL record from segment from position indicated by LSN.
void	startBackgroundWrite() Start background task which performs periodical write of background buffer to the disk.
void	stopBackgroundWrite(boolean flush) Stop background task which writes data from log segments buffer to the disk and writes the rest of the buffer to the disk.

Methods inherited from interface java.lang.Comparable

compareTo

Method Detail

getOrder

long getOrder()

Returns:

index if segment inside of WAL.

init

void init()
   throws IOException

This method should be called before segment started to be used by WAL. It performs initialisation of internal state of segment.

Throws:

IOException

filledUpTo

long filledUpTo()

Returns:

length of segment in pages.

begin

OLogSequenceNumber begin()
                  throws IOException

Returns:

LSN of first record contained inside of segment.

Throws:

IOException

end

OLogSequenceNumber end()

Returns:

LSN of last record contained inside of segment.

getPath

String getPath()

Returns:

Location of the buffer inside the file system.

logRecord

OLogSequenceNumber logRecord(byte[] record)

Appends new records to the WAL segment and returns LSN of it.

readRecord

byte[] readRecord(OLogSequenceNumber lsn)
           throws IOException

Reads WAL record from segment from position indicated by LSN.

Throws:

IOException

getNextLSN

OLogSequenceNumber getNextLSN(OLogSequenceNumber lsn)
                       throws IOException

Returns LSN of the record which follows after the record with passed in LSN. If passed in LSN belongs to the last record null is returned.

Throws:

IOException

close

void close(boolean flush)
    throws IOException

Writes buffer of the segment to the disk and closes all acquired resources. Performs fsync of data if necessary.

Throws:

IOException

flush

void flush()

Writes buffer of the segment to the disk and performs fsync of data.

delete

void delete()
     throws IOException

Clears the buffer and deletes file content.

Throws:

IOException

stopBackgroundWrite

void stopBackgroundWrite(boolean flush)

Stop background task which writes data from log segments buffer to the disk and writes the rest of the buffer to the disk. Performs fsync if necessary.

startBackgroundWrite

void startBackgroundWrite()

Start background task which performs periodical write of background buffer to the disk.