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 assumed to be atomic, single-writer, write-once, multiple-readers, ready-many type of objects. To ensure this, any implementation of this interface must. 1) Return a CheckpointID to a client only upon the successful commit of the checkpoint. 2) Prevent any checkpoint from being re-opened for writes.

Non-functional properties such as durability, availability, compression, garbage collection, and 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) Aborts the current checkpoint.
CheckpointID	commit(CheckpointService.CheckpointWriteChannel channel) Closes an existing checkpoint for writes and returns the CheckpointID that can be later used to get the read-only access to this checkpoint.
CheckpointService.CheckpointWriteChannel	create() Creates a checkpoint and provides a channel to write to it.
boolean	delete(CheckpointID checkpointId) Discards an existing checkpoint identified by its CheckpointID.
CheckpointService.CheckpointReadChannel	open(CheckpointID checkpointId) Returns a reading channel to a checkpoint identified by the CheckpointID.

Method Detail

create

CheckpointService.CheckpointWriteChannel create()
                                                throws IOException,
                                                       InterruptedException

Creates a checkpoint and provides 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

Closes an existing checkpoint for writes and returns the CheckpointID that can be later used to get the read-only access to this checkpoint. Implementation is supposed to return the CheckpointID to the caller only on the successful completion of checkpoint to guarantee 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

Aborts the current checkpoint. Garbage collection choices are left to the implementation. The CheckpointID is neither generated nor released to the client so the checkpoint is not accessible.

Parameters:

channel - the CheckpointWriteChannel to abort

Throws:

IOException

InterruptedException

open

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

Returns a reading channel to a checkpoint identified by the CheckpointID.

Parameters:

checkpointId - CheckpointID for the checkpoint to be opened

Returns:

a CheckpointReadChannel

Throws:

IOException

InterruptedException

delete

boolean delete(CheckpointID checkpointId)
               throws IOException,
                      InterruptedException

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