Package org.apache.jackrabbit.oak.plugins.cow

Class COWNodeStore

java.lang.Object

org.apache.jackrabbit.oak.plugins.cow.COWNodeStore

All Implemented Interfaces:

Observable, NodeStore

public class COWNodeStore
extends Object
implements NodeStore, Observable

The copy-on-write (COW) node store implementation allows to temporarily switch the repository into the "testing" mode, in which all the changes are stored in a volatile storage, namely the MemoryNodeStore. After switching back to the "production" mode, the test changes should be dropped.

If the CoW is enabled, a special :cow=true property will be set on the root node returned by getRoot(). It's being used in the merge() to decide which store be modified. Removing this property will result in merging changes to the main node store, even in the CoW mode.

The checkpoint support is provided by the BranchNodeStore class. All the existing checkpoints are still available in the CoW mode (until they expire). New checkpoints are only created in the MemoryNodeStore.

Known limitations:

• turning the CoW mode on and off requires cleaning up the lucene indexing cache,
• switching the CoW mode may result in repository inconsistencies (eg. if two merges belongs to the same logical commit sequence),
• in the CoW mode the changes are stored in MemoryNodeStore, so it shouldn't be enabled for too long (otherwise it may exhaust the heap).

Constructor Summary

Constructors

Constructor	Description
COWNodeStore(NodeStore store)

Method Summary

Modifier and Type	Method	Description
Closeable	addObserver(Observer observer)	Register a new Observer.
@NotNull String	checkpoint(long lifetime)	Creates a new checkpoint of the latest root of the tree.
@NotNull String	checkpoint(long lifetime, @NotNull Map<String,String> properties)	Creates a new checkpoint of the latest root of the tree.
@NotNull Map<String,String>	checkpointInfo(@NotNull String checkpoint)	Retrieve the properties associated with a checkpoint.
@NotNull Iterable<String>	checkpoints()	Returns all valid checkpoints.
@NotNull Blob	createBlob(InputStream inputStream)	Create a Blob from the given input stream.
void	disableCopyOnWrite()
void	enableCopyOnWrite()
Blob	getBlob(@NotNull String reference)	Get a blob by its reference.
@NotNull NodeState	getRoot()	Returns the latest state of the tree.
@NotNull NodeState	merge(@NotNull NodeBuilder builder, @NotNull CommitHook commitHook, @NotNull CommitInfo info)	Merges the changes between the base and head states of the given builder to this store.
@NotNull NodeState	rebase(@NotNull NodeBuilder builder)	Rebases the changes between the base and head states of the given builder on top of the current root state.
boolean	release(@NotNull String checkpoint)	Releases the provided checkpoint.
NodeState	reset(@NotNull NodeBuilder builder)	Reset the passed builder by throwing away all its changes and setting its base state to the current root state.
NodeState	retrieve(@NotNull String checkpoint)	Retrieves the root node from a previously created repository checkpoint.

Methods inherited from class java.lang.Object

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

Constructor Detail

COWNodeStore

public COWNodeStore(NodeStore store)

Method Detail

enableCopyOnWrite

public void enableCopyOnWrite()
                       throws CommitFailedException

Throws:

CommitFailedException

disableCopyOnWrite

public void disableCopyOnWrite()

addObserver

public Closeable addObserver(Observer observer)

Description copied from interface: Observable

Register a new Observer. Clients need to call Closeable.close() to stop getting notifications on the registered observer and to free up any resources associated with the registration.

Specified by:

addObserver in interface Observable

Returns:

a Closeable instance.

getRoot

@NotNull
public @NotNull NodeState getRoot()

Description copied from interface: NodeStore

Returns the latest state of the tree.

Specified by:

getRoot in interface NodeStore

Returns:

root node state

merge

@NotNull
public @NotNull NodeState merge(@NotNull
                                @NotNull NodeBuilder builder,
                                @NotNull
                                @NotNull CommitHook commitHook,
                                @NotNull
                                @NotNull CommitInfo info)
                         throws CommitFailedException

Description copied from interface: NodeStore

Merges the changes between the base and head states of the given builder to this store.

Specified by:

merge in interface NodeStore

Parameters:

builder - the builder whose changes to apply

commitHook - the commit hook to apply while merging changes

info - commit info associated with this merge operation

Returns:

the node state resulting from the merge.

Throws:

CommitFailedException - if the merge failed

rebase

@NotNull
public @NotNull NodeState rebase(@NotNull
                                 @NotNull NodeBuilder builder)

Description copied from interface: NodeStore

Rebases the changes between the base and head states of the given builder on top of the current root state. The base state of the given builder becomes the latest root state of the repository, and the head state will contain the rebased changes.

Specified by:

rebase in interface NodeStore

Parameters:

builder - the builder to rebase

Returns:

the node state resulting from the rebase.

reset

public NodeState reset(@NotNull
                       @NotNull NodeBuilder builder)

Description copied from interface: NodeStore

Reset the passed builder by throwing away all its changes and setting its base state to the current root state.

Specified by:

reset in interface NodeStore

Parameters:

builder - the builder to reset

Returns:

the node state resulting from the reset.

createBlob

@NotNull
public @NotNull Blob createBlob(InputStream inputStream)
                         throws IOException

Description copied from interface: NodeStore

Create a Blob from the given input stream. The input stream is closed after this method returns.

Specified by:

createBlob in interface NodeStore

Parameters:

inputStream - The input stream for the Blob

Returns:

The Blob representing inputStream

Throws:

IOException - If an error occurs while reading from the stream

getBlob

public Blob getBlob(@NotNull
                    @NotNull String reference)

Description copied from interface: NodeStore

Get a blob by its reference.

Specified by:

getBlob in interface NodeStore

Parameters:

reference - reference to the blob

Returns:

blob or null if the reference does not resolve to a blob.

See Also:

Blob.getReference()

checkpoint

@NotNull
public @NotNull String checkpoint(long lifetime,
                                  @NotNull
                                  @NotNull Map<String,String> properties)

Description copied from interface: NodeStore

Creates a new checkpoint of the latest root of the tree. The checkpoint remains valid for at least as long as requested and allows that state of the repository to be retrieved using the returned opaque string reference.

The properties passed to this methods are associated with the checkpoint and can be retrieved through the NodeStore.checkpointInfo(String) method. Its semantics is entirely application specific.

Specified by:

checkpoint in interface NodeStore

Parameters:

lifetime - time (in milliseconds, > 0) that the checkpoint should remain available

properties - properties to associate with the checkpoint

Returns:

string reference of this checkpoint

checkpoint

@NotNull
public @NotNull String checkpoint(long lifetime)

Description copied from interface: NodeStore

Creates a new checkpoint of the latest root of the tree. The checkpoint remains valid for at least as long as requested and allows that state of the repository to be retrieved using the returned opaque string reference.

This method is a shortcut for NodeStore.checkpoint(long, Map) passing an empty map for its 2nd argument.

Specified by:

checkpoint in interface NodeStore

Parameters:

lifetime - time (in milliseconds, > 0) that the checkpoint should remain available

Returns:

string reference of this checkpoint

checkpointInfo

@NotNull
public @NotNull Map<String,String> checkpointInfo(@NotNull
                                                        @NotNull String checkpoint)

Description copied from interface: NodeStore

Retrieve the properties associated with a checkpoint.

Specified by:

checkpointInfo in interface NodeStore

Parameters:

checkpoint - string reference of a checkpoint

Returns:

the properties associated with the checkpoint referenced by checkpoint or an empty map when there is no such checkpoint.

checkpoints

@NotNull
public @NotNull Iterable<String> checkpoints()

Description copied from interface: NodeStore

Returns all valid checkpoints. The returned Iterable provides a snapshot of valid checkpoints at the time this method is called. That is, the Iterable will not reflect checkpoints created after this method was called.

See NodeStore.checkpoint(long, Map) for a definition of a valid checkpoint.

Specified by:

checkpoints in interface NodeStore

Returns:

valid checkpoints.

retrieve

public NodeState retrieve(@NotNull
                          @NotNull String checkpoint)

Description copied from interface: NodeStore

Retrieves the root node from a previously created repository checkpoint.

Specified by:

retrieve in interface NodeStore

Parameters:

checkpoint - string reference of a checkpoint

Returns:

the root node of the checkpoint, or null if the checkpoint is no longer available

release

public boolean release(@NotNull
                       @NotNull String checkpoint)

Description copied from interface: NodeStore

Releases the provided checkpoint. If the provided checkpoint doesn't exist this method should return true.

Specified by:

release in interface NodeStore

Parameters:

checkpoint - string reference of a checkpoint

Returns:

true if the checkpoint was successfully removed, or if it doesn't exist