org.apache.flink.runtime.state.CheckpointStorage Maven / Gradle / Ivy
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* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.flink.runtime.state;
import org.apache.flink.runtime.state.CheckpointStreamFactory.CheckpointStateOutputStream;
import javax.annotation.Nullable;
import java.io.IOException;
/**
* CheckpointStorage implements the durable storage of checkpoint data and metadata streams.
* An individual checkpoint or savepoint is stored to a {@link CheckpointStorageLocation},
* created by this class.
*/
public interface CheckpointStorage {
/**
* Checks whether this backend supports highly available storage of data.
*
* Some state backends may not support highly-available durable storage, with default settings,
* which makes them suitable for zero-config prototyping, but not for actual production setups.
*/
boolean supportsHighlyAvailableStorage();
/**
* Checks whether the storage has a default savepoint location configured.
*/
boolean hasDefaultSavepointLocation();
/**
* Resolves the given pointer to a checkpoint/savepoint into a checkpoint location. The location
* supports reading the checkpoint metadata, or disposing the checkpoint storage location.
*
*
If the state backend cannot understand the format of the pointer (for example because it
* was created by a different state backend) this method should throw an {@code IOException}.
*
* @param externalPointer The external checkpoint pointer to resolve.
* @return The checkpoint location handle.
*
* @throws IOException Thrown, if the state backend does not understand the pointer, or if
* the pointer could not be resolved due to an I/O error.
*/
CompletedCheckpointStorageLocation resolveCheckpoint(String externalPointer) throws IOException;
/**
* Resolves the given pointer to a checkpoint/savepoint into the latest completed checkpoint location.
* The location supports reading the checkpoint metadata, or disposing the checkpoint storage location.
*
*
If the state backend cannot understand the format of the pointer (for example because it
* was created by a different state backend) this method should throw an {@code IOException}.
*
* @param externalPointer The external checkpoint pointer to resolve.
* @return The latest completed checkpoint location handle.
*
* @throws IOException Thrown, if the state backend does not understand the pointer, or if
* the pointer could not be resolved due to an I/O error.
*/
CompletedCheckpointStorageLocation resolveLatestCheckpoint(String externalPointer) throws IOException;
/**
* Initializes a storage location for new checkpoint with the given ID.
*
*
The returned storage location can be used to write the checkpoint data and metadata
* to and to obtain the pointers for the location(s) where the actual checkpoint data should be
* stored.
*
* @param checkpointId The ID (logical timestamp) of the checkpoint that should be persisted.
* @return A storage location for the data and metadata of the given checkpoint.
*
* @throws IOException Thrown if the storage location cannot be initialized due to an I/O exception.
*/
CheckpointStorageLocation initializeLocationForCheckpoint(long checkpointId) throws IOException;
/**
* Initializes a storage location for new savepoint with the given ID.
*
*
If an external location pointer is passed, the savepoint storage location
* will be initialized at the location of that pointer. If the external location pointer is null,
* the default savepoint location will be used. If no default savepoint location is configured,
* this will throw an exception. Whether a default savepoint location is configured can be
* checked via {@link #hasDefaultSavepointLocation()}.
*
* @param checkpointId The ID (logical timestamp) of the savepoint's checkpoint.
* @param externalLocationPointer Optionally, a pointer to the location where the savepoint should
* be stored. May be null.
*
* @return A storage location for the data and metadata of the savepoint.
*
* @throws IOException Thrown if the storage location cannot be initialized due to an I/O exception.
*/
CheckpointStorageLocation initializeLocationForSavepoint(
long checkpointId,
@Nullable String externalLocationPointer) throws IOException;
/**
* Resolves a storage location reference into a CheckpointStreamFactory.
*
*
The reference may be the {@link CheckpointStorageLocationReference#isDefaultReference() default reference},
* in which case the method should return the default location, taking existing configuration
* and checkpoint ID into account.
*
* @param checkpointId The ID of the checkpoint that the location is initialized for.
* @param reference The checkpoint location reference.
*
* @return A checkpoint storage location reflecting the reference and checkpoint ID.
*
* @throws IOException Thrown, if the storage location cannot be initialized from the reference.
*/
CheckpointStreamFactory resolveCheckpointStorageLocation(
long checkpointId,
CheckpointStorageLocationReference reference) throws IOException;
/**
* Opens a stream to persist checkpoint state data that is owned strictly by tasks and
* not attached to the life cycle of a specific checkpoint.
*
*
This method should be used when the persisted data cannot be immediately dropped once
* the checkpoint that created it is dropped. Examples are write-ahead-logs.
* For those, the state can only be dropped once the data has been moved to the target system,
* which may sometimes take longer than one checkpoint (if the target system is temporarily unable
* to keep up).
*
*
The fact that the job manager does not own the life cycle of this type of state means also
* that it is strictly the responsibility of the tasks to handle the cleanup of this data.
*
*
Developer note: In the future, we may be able to make this a special case of "shared state",
* where the task re-emits the shared state reference as long as it needs to hold onto the
* persisted state data.
*
* @return A checkpoint state stream to the location for state owned by tasks.
* @throws IOException Thrown, if the stream cannot be opened.
*/
CheckpointStateOutputStream createTaskOwnedStateStream() throws IOException;
}