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

Class OWALPageV1

java.lang.Object

com.orientechnologies.orient.core.storage.impl.local.paginated.wal.OWALPageV1

All Implemented Interfaces:

OWALPage

public class OWALPageV1
extends Object
implements OWALPage

WAL page is organized using following format:

1. CRC32 code of page content, it is used to check whether data are broken on disk. 4 bytes
2. Magic number, randomly generated number which is used to check whether page is broken on disk. 8 bytes
3. Amount of free space left on page, which can be used to add new records, 4 bytes
4. WAL records

Each WAL record is stored using following format:

1. Flag which indicates that record should be merged with record which is stored on next page. That is needed if record can not be stored on one page and is split by two pages. 1 byte
2. Flag which indicates that this record is actually tail of long record parts of which are stored on other pages, 1 byte
3. Length of serialized content of WAL record. 4 bytes
4. Serialized content of the WAL record. Variable size.

Every time new record is added. Value of free space left on page is updated.

Since:

5/8/13

Author:

Andrey Lomakin

Field Summary

Fields inherited from interface com.orientechnologies.orient.core.storage.impl.local.paginated.wal.OWALPage

CRC_OFFSET, FREE_SPACE_OFFSET, MAGIC_NUMBER_OFFSET, MIN_RECORD_SIZE, PAGE_SIZE

Method Summary

Modifier and Type	Method and Description
int	getFreeSpace()
byte[]	getRecord(int position) Returns content of record which is stored inside of specified position of page.
boolean	mergeWithNextPage(int position) Indicates whether page stored inside of passed in position is stored only partially inside of given page, so next part of the record should be read from next page of WAL segment.

Methods inherited from class java.lang.Object

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

Method Detail

getRecord

public byte[] getRecord(int position)

Returns content of record which is stored inside of specified position of page.

Specified by:

getRecord in interface OWALPage

mergeWithNextPage

public boolean mergeWithNextPage(int position)

Indicates whether page stored inside of passed in position is stored only partially inside of given page, so next part of the record should be read from next page of WAL segment.

Specified by:

mergeWithNextPage in interface OWALPage

getFreeSpace

public int getFreeSpace()

Specified by:

getFreeSpace in interface OWALPage

Returns:

Amount of free space available to store new records inside of page.