Package org.apache.hadoop.hbase.regionserver

Class MultiVersionConcurrencyControl

java.lang.Object

org.apache.hadoop.hbase.regionserver.MultiVersionConcurrencyControl

@Private
public class MultiVersionConcurrencyControl
extends Object

Manages the read/write consistency. This provides an interface for readers to determine what entries to ignore, and a mechanism for writers to obtain new write numbers, then "commit" the new writes for readers to read (thus forming atomic transactions).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	MultiVersionConcurrencyControl.WriteEntry	Write number and whether write has completed given out at start of a write transaction.

Field Summary

Fields

Modifier and Type	Field	Description
static final long	FIXED_SIZE
private static final org.slf4j.Logger	LOG
static final long	NONE	Represents no value, or not set.
(package private) final AtomicLong	readPoint
private static final long	READPOINT_ADVANCE_WAIT_TIME
private final Object	readWaiters
(package private) final String	regionName
(package private) final AtomicLong	writePoint
private final LinkedList<MultiVersionConcurrencyControl.WriteEntry>	writeQueue

Constructor Summary

Constructors

Constructor	Description
MultiVersionConcurrencyControl()
MultiVersionConcurrencyControl(long startPoint)	Construct and set read point.
MultiVersionConcurrencyControl(String regionName)

Method Summary

Modifier and Type	Method	Description
void	advanceTo(long newStartPoint)	Step the MVCC forward on to a new read/write basis.
void	await()	Wait until the read point catches up to the write point; i.e.
MultiVersionConcurrencyControl.WriteEntry	begin()	Call begin(Runnable) with an empty Runnable.
MultiVersionConcurrencyControl.WriteEntry	begin(Runnable action)	Start a write transaction.
boolean	complete(MultiVersionConcurrencyControl.WriteEntry writeEntry)	Mark the MultiVersionConcurrencyControl.WriteEntry as complete and advance the read point as much as possible.
void	completeAndWait(MultiVersionConcurrencyControl.WriteEntry e)	Complete a MultiVersionConcurrencyControl.WriteEntry that was created by begin() then wait until the read point catches up to our write.
long	getReadPoint()
long	getWritePoint()
String	toString()
(package private) boolean	tryAdvanceTo(long newStartPoint, long expected)	Step the MVCC forward on to a new read/write basis.
(package private) void	waitForRead(MultiVersionConcurrencyControl.WriteEntry e)	Wait for the global readPoint to advance up to the passed in write entry number.

Methods inherited from class java.lang.Object

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

Field Details

LOG

private static final org.slf4j.Logger LOG

READPOINT_ADVANCE_WAIT_TIME

private static final long READPOINT_ADVANCE_WAIT_TIME

See Also:

• Constant Field Values

regionName

final String regionName

readPoint

final AtomicLong readPoint

writePoint

final AtomicLong writePoint

readWaiters

private final Object readWaiters

NONE

public static final long NONE

Represents no value, or not set.

See Also:

• Constant Field Values

writeQueue

private final LinkedList<MultiVersionConcurrencyControl.WriteEntry> writeQueue

FIXED_SIZE

public static final long FIXED_SIZE

Constructor Details

MultiVersionConcurrencyControl

public MultiVersionConcurrencyControl()

MultiVersionConcurrencyControl

public MultiVersionConcurrencyControl(String regionName)

MultiVersionConcurrencyControl

public MultiVersionConcurrencyControl(long startPoint)

Construct and set read point. Write point is uninitialized.

Method Details

advanceTo

public void advanceTo(long newStartPoint)

Step the MVCC forward on to a new read/write basis.

tryAdvanceTo

boolean tryAdvanceTo(long newStartPoint,
 long expected)

Step the MVCC forward on to a new read/write basis.

Parameters:

newStartPoint - Point to move read and write points to.

expected - If not -1 (#NONE)

Returns:

Returns false if expected is not equal to the current readPoint or if startPoint is less than current readPoint

begin

public MultiVersionConcurrencyControl.WriteEntry begin()

Call begin(Runnable) with an empty Runnable.

begin

public MultiVersionConcurrencyControl.WriteEntry begin(Runnable action)

Start a write transaction. Create a new MultiVersionConcurrencyControl.WriteEntry with a new write number and add it to our queue of ongoing writes. Return this WriteEntry instance. To complete the write transaction and wait for it to be visible, call completeAndWait(WriteEntry). If the write failed, call complete(WriteEntry) so we can clean up AFTER removing ALL trace of the failed write transaction.

The action will be executed under the lock which means it can keep the same order with mvcc.

See Also:

• complete(WriteEntry)
• completeAndWait(WriteEntry)

await

public void await()

Wait until the read point catches up to the write point; i.e. wait on all outstanding mvccs to complete.

completeAndWait

public void completeAndWait(MultiVersionConcurrencyControl.WriteEntry e)

Complete a MultiVersionConcurrencyControl.WriteEntry that was created by begin() then wait until the read point catches up to our write. At the end of this call, the global read point is at least as large as the write point of the passed in WriteEntry. Thus, the write is visible to MVCC readers.

complete

public boolean complete(MultiVersionConcurrencyControl.WriteEntry writeEntry)

Mark the MultiVersionConcurrencyControl.WriteEntry as complete and advance the read point as much as possible. Call this even if the write has FAILED (AFTER backing out the write transaction changes completely) so we can clean up the outstanding transaction. How much is the read point advanced? Let S be the set of all write numbers that are completed. Set the read point to the highest numbered write of S.

Returns:

true if e is visible to MVCC readers (that is, readpoint >= e.writeNumber)

waitForRead

void waitForRead(MultiVersionConcurrencyControl.WriteEntry e)

Wait for the global readPoint to advance up to the passed in write entry number.

toString

public String toString()

Overrides:

toString in class Object

getReadPoint

public long getReadPoint()

getWritePoint

public long getWritePoint()