org.apache.ignite.internal.pagemem

Class FullPageId

java.lang.Object

org.apache.ignite.internal.pagemem.FullPageId

public class FullPageId
extends Object

Compound object used to address a page in the global page space.

Page ID structure

Generally, a full page ID consists of a cache ID and page ID. A page ID consists of page index (32 bits), partition ID (16 bits) and flags. Higher 8 bits of page ID are unused and reserved to address entries inside data pages or page ID rotation.

Partition ID 0xFFFF is reserved for index pages.

The structure of a page ID is shown in the diagram below:

 +---------+-----------+------------+--------------------------+
 | 8 bits  |   8 bits  |  16 bits   |         32 bits          |
 +---------+-----------+------------+--------------------------+
 |  OFFSET |   FLAGS   |PARTITION ID|       PAGE INDEX         |
 +---------+-----------+------------+--------------------------+
 

 
Page ID rotation
 There are scenarios when we reference one page (B) from within another page (A) by page ID. It is also
 possible that this first page (B) is concurrently reused for a different purpose. In this
 case we should have a mechanism to determine that the reference from page (A) to page (B) is no longer valid.
 This is ensured by page ID rotation - together with page's (B) ID we should write some value that is incremented
 each time a page is reused (page ID rotation). This ID should be verified after page read and a page
 should be discarded if full ID is different.
 

 Effective page ID is page ID with zeroed bits used for page ID rotation.

Field Summary

Fields

Modifier and Type	Field and Description
static FullPageId	NULL_PAGE

Constructor Summary

Constructors

Constructor and Description
FullPageId(long pageId, int grpId)

Method Summary

Modifier and Type	Method and Description
long	effectivePageId()
boolean	equals(Object o)
int	groupId()
int	hashCode()
static int	hashCode(int grpId, long pageId)
long	pageId()
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

NULL_PAGE

public static final FullPageId NULL_PAGE

Constructor Detail

FullPageId

public FullPageId(long pageId,
                  int grpId)

Parameters:

pageId - Page ID.

grpId - Cache group ID.

Method Detail

hashCode

public static int hashCode(int grpId,
                           long pageId)

Parameters:

grpId - Cache group ID.

pageId - Page ID.

Returns:

Hash code.

pageId

public long pageId()

Returns:

Page ID.

effectivePageId

public long effectivePageId()

Returns:

Effective page ID.

groupId

public int groupId()

Returns:

Cache group ID.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object