org.apache.reef.io.checkpoint

Interface CheckpointService

All Known Implementing Classes:

FSCheckpointService

public interface CheckpointService

The CheckpointService provides a simple API to store and retrieve the state of a task.

Checkpoints are atomic, single-writer, write-once, multiple-readers, ready-many type of objects. This is provided by releasing the CheckpointID for a checkpoint only upon commit of the checkpoint, and by preventing a checkpoint to be re-opened for writes.

Non-functional properties such as durability, availability, compression, garbage collection, quotas are left to the implementation.

This API is envisioned as the basic building block for a checkpoint service, on top of which richer interfaces can be layered (e.g., frameworks providing object-serialization, checkpoint metadata and provenance, etc.)

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	CheckpointService.CheckpointReadChannel A channel to read from a checkpoint.
static interface	CheckpointService.CheckpointWriteChannel A channel to write to a checkpoint.

Method Summary

Methods

Modifier and Type	Method and Description
void	abort(CheckpointService.CheckpointWriteChannel channel) Dual to commit, it aborts the current checkpoint.
CheckpointID	commit(CheckpointService.CheckpointWriteChannel channel) Used to finalize and existing checkpoint.
CheckpointService.CheckpointWriteChannel	create() This method creates a checkpoint and provide a channel to write to it.
boolean	delete(CheckpointID checkpointId) It discards an existing checkpoint identified by its CheckpointID.
CheckpointService.CheckpointReadChannel	open(CheckpointID checkpointId) Given a CheckpointID returns a reading channel.

Method Detail

create

CheckpointService.CheckpointWriteChannel create()
                                                throws IOException,
                                                       InterruptedException

This method creates a checkpoint and provide a channel to write to it. The name/location of the checkpoint are unknown to the user as of this time, in fact, the CheckpointID is not released to the user until commit is called. This makes enforcing atomicity of writes easy.

Returns:

a CheckpointWriteChannel that can be used to write to the checkpoint

Throws:

IOException

InterruptedException

commit

CheckpointID commit(CheckpointService.CheckpointWriteChannel channel)
                    throws IOException,
                           InterruptedException

Used to finalize and existing checkpoint. It returns the CheckpointID that can be later used to access (read-only) this checkpoint. This guarantees atomicity of the checkpoint.

Parameters:

channel - the CheckpointWriteChannel to commit

Returns:

a CheckpointID

Throws:

IOException

InterruptedException

abort

void abort(CheckpointService.CheckpointWriteChannel channel)
           throws IOException,
                  InterruptedException

Dual to commit, it aborts the current checkpoint. Garbage collection choices are left to the implementation. The CheckpointID is not generated nor released to the user so the checkpoint is not accessible.

Parameters:

channel - the CheckpointWriteChannel to abort

Throws:

IOException

InterruptedException

open

CheckpointService.CheckpointReadChannel open(CheckpointID checkpointId)
                                             throws IOException,
                                                    InterruptedException

Given a CheckpointID returns a reading channel.

Parameters:

checkpointId - CheckpointID for the checkpoint to be opened

Returns:

a CheckpointReadChannel

Throws:

IOException

InterruptedException

delete

boolean delete(CheckpointID checkpointId)
               throws IOException,
                      InterruptedException

It discards an existing checkpoint identified by its CheckpointID.

Parameters:

checkpointId - CheckpointID for the checkpoint to be deleted

Returns:

a boolean confirming success of the deletion

Throws:

IOException

InterruptedException