org.apache.flink.runtime.state.memory

Class MemoryStateBackend

java.lang.Object

org.apache.flink.runtime.state.AbstractStateBackend

org.apache.flink.runtime.state.filesystem.AbstractFileStateBackend

org.apache.flink.runtime.state.memory.MemoryStateBackend

All Implemented Interfaces:

Serializable, ConfigurableStateBackend, StateBackend

@PublicEvolving
public class MemoryStateBackend
extends AbstractFileStateBackend
implements ConfigurableStateBackend

This state backend holds the working state in the memory (JVM heap) of the TaskManagers. The state backend checkpoints state directly to the JobManager's memory (hence the backend's name), but the checkpoints will be persisted to a file system for high-availability setups and savepoints. The MemoryStateBackend is consequently a FileSystem-based backend that can work without a file system dependency in simple setups.

This state backend should be used only for experimentation, quick local setups, or for streaming applications that have very small state: Because it requires checkpoints to go through the JobManager's memory, larger state will occupy larger portions of the JobManager's main memory, reducing operational stability. For any other setup, the FsStateBackend should be used. The FsStateBackend holds the working state on the TaskManagers in the same way, but checkpoints state directly to files rather then to the JobManager's memory, thus supporting large state sizes.

State Size Considerations

State checkpointing with this state backend is subject to the following conditions:

• Each individual state must not exceed the configured maximum state size (see getMaxStateSize().
• All state from one task (i.e., the sum of all operator states and keyed states from all chained operators of the task) must not exceed what the RPC system supports, which is be default < 10 MB. That limit can be configured up, but that is typically not advised.
• The sum of all states in the application times all retained checkpoints must comfortably fit into the JobManager's JVM heap space.

Persistence Guarantees

For the use cases where the state sizes can be handled by this backend, the backend does guarantee persistence for savepoints, externalized checkpoints (of configured), and checkpoints (when high-availability is configured).

Configuration

As for all state backends, this backend can either be configured within the application (by creating the backend with the respective constructor parameters and setting it on the execution environment) or by specifying it in the Flink configuration.

If the state backend was specified in the application, it may pick up additional configuration parameters from the Flink configuration. For example, if the backend if configured in the application without a default savepoint directory, it will pick up a default savepoint directory specified in the Flink configuration of the running job/cluster. That behavior is implemented via the configure(Configuration) method.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_MAX_STATE_SIZE The default maximal size that the snapshotted memory state may have (5 MiBytes).

Constructor Summary

Constructors

Constructor and Description
MemoryStateBackend() Creates a new memory state backend that accepts states whose serialized forms are up to the default state size (5 MB).
MemoryStateBackend(boolean asynchronousSnapshots) Creates a new memory state backend that accepts states whose serialized forms are up to the default state size (5 MB).
MemoryStateBackend(int maxStateSize) Creates a new memory state backend that accepts states whose serialized forms are up to the given number of bytes.
MemoryStateBackend(int maxStateSize, boolean asynchronousSnapshots) Creates a new memory state backend that accepts states whose serialized forms are up to the given number of bytes and that uses asynchronous snashots as configured.
MemoryStateBackend(String checkpointPath, String savepointPath) Creates a new MemoryStateBackend, setting optionally the path to persist checkpoint metadata to, and to persist savepoints to.
MemoryStateBackend(String checkpointPath, String savepointPath, int maxStateSize, TernaryBoolean asynchronousSnapshots) Creates a new MemoryStateBackend, setting optionally the paths to persist checkpoint metadata and savepoints to, as well as configuring state thresholds and asynchronous operations.

Method Summary

Modifier and Type	Method and Description
MemoryStateBackend	configure(Configuration config) Creates a copy of this state backend that uses the values defined in the configuration for fields where that were not specified in this state backend.
CheckpointStorage	createCheckpointStorage(JobID jobId) Creates a storage for checkpoints for the given job.
<K> AbstractKeyedStateBackend<K>	createKeyedStateBackend(Environment env, JobID jobID, String operatorIdentifier, TypeSerializer<K> keySerializer, int numberOfKeyGroups, KeyGroupRange keyGroupRange, TaskKvStateRegistry kvStateRegistry, TtlTimeProvider ttlTimeProvider) Creates a new AbstractKeyedStateBackend that is responsible for holding keyed state and checkpointing it.
OperatorStateBackend	createOperatorStateBackend(Environment env, String operatorIdentifier) Creates a new OperatorStateBackend that can be used for storing operator state.
int	getMaxStateSize() Gets the maximum size that an individual state can have, as configured in the constructor (by default 5242880).
boolean	isUsingAsynchronousSnapshots() Gets whether the key/value data structures are asynchronously snapshotted.
String	toString()

Methods inherited from class org.apache.flink.runtime.state.filesystem.AbstractFileStateBackend

getCheckpointPath, getSavepointPath, resolveCheckpoint

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.flink.runtime.state.StateBackend

createKeyedStateBackend

Field Detail

DEFAULT_MAX_STATE_SIZE

public static final int DEFAULT_MAX_STATE_SIZE

The default maximal size that the snapshotted memory state may have (5 MiBytes).

See Also:

Constant Field Values

Constructor Detail

MemoryStateBackend

public MemoryStateBackend()

Creates a new memory state backend that accepts states whose serialized forms are up to the default state size (5 MB).

Checkpoint and default savepoint locations are used as specified in the runtime configuration.

MemoryStateBackend

public MemoryStateBackend(boolean asynchronousSnapshots)

Creates a new memory state backend that accepts states whose serialized forms are up to the default state size (5 MB). The state backend uses asynchronous snapshots or synchronous snapshots as configured.

Checkpoint and default savepoint locations are used as specified in the runtime configuration.

Parameters:

asynchronousSnapshots - Switch to enable asynchronous snapshots.

MemoryStateBackend

public MemoryStateBackend(int maxStateSize)

Creates a new memory state backend that accepts states whose serialized forms are up to the given number of bytes.

Checkpoint and default savepoint locations are used as specified in the runtime configuration.

WARNING: Increasing the size of this value beyond the default value (5242880) should be done with care. The checkpointed state needs to be send to the JobManager via limited size RPC messages, and there and the JobManager needs to be able to hold all aggregated state in its memory.

Parameters:

maxStateSize - The maximal size of the serialized state

MemoryStateBackend

public MemoryStateBackend(int maxStateSize,
                          boolean asynchronousSnapshots)

Creates a new memory state backend that accepts states whose serialized forms are up to the given number of bytes and that uses asynchronous snashots as configured.

Checkpoint and default savepoint locations are used as specified in the runtime configuration.

WARNING: Increasing the size of this value beyond the default value (5242880) should be done with care. The checkpointed state needs to be send to the JobManager via limited size RPC messages, and there and the JobManager needs to be able to hold all aggregated state in its memory.

Parameters:

maxStateSize - The maximal size of the serialized state

asynchronousSnapshots - Switch to enable asynchronous snapshots.

MemoryStateBackend

public MemoryStateBackend(@Nullable
                          String checkpointPath,
                          @Nullable
                          String savepointPath)

Creates a new MemoryStateBackend, setting optionally the path to persist checkpoint metadata to, and to persist savepoints to.

Parameters:

checkpointPath - The path to write checkpoint metadata to. If null, the value from the runtime configuration will be used.

savepointPath - The path to write savepoints to. If null, the value from the runtime configuration will be used.

MemoryStateBackend

public MemoryStateBackend(@Nullable
                          String checkpointPath,
                          @Nullable
                          String savepointPath,
                          int maxStateSize,
                          TernaryBoolean asynchronousSnapshots)

Creates a new MemoryStateBackend, setting optionally the paths to persist checkpoint metadata and savepoints to, as well as configuring state thresholds and asynchronous operations.

WARNING: Increasing the size of this value beyond the default value (5242880) should be done with care. The checkpointed state needs to be send to the JobManager via limited size RPC messages, and there and the JobManager needs to be able to hold all aggregated state in its memory.

Parameters:

checkpointPath - The path to write checkpoint metadata to. If null, the value from the runtime configuration will be used.

savepointPath - The path to write savepoints to. If null, the value from the runtime configuration will be used.

maxStateSize - The maximal size of the serialized state.

asynchronousSnapshots - Flag to switch between synchronous and asynchronous snapshot mode. If null, the value configured in the runtime configuration will be used.

Method Detail

getMaxStateSize

public int getMaxStateSize()

Gets the maximum size that an individual state can have, as configured in the constructor (by default 5242880).

Returns:

The maximum size that an individual state can have

isUsingAsynchronousSnapshots

public boolean isUsingAsynchronousSnapshots()

Gets whether the key/value data structures are asynchronously snapshotted.

If not explicitly configured, this is the default value of CheckpointingOptions.ASYNC_SNAPSHOTS.

configure

public MemoryStateBackend configure(Configuration config)

Creates a copy of this state backend that uses the values defined in the configuration for fields where that were not specified in this state backend.

Specified by:

configure in interface ConfigurableStateBackend

Parameters:

config - the configuration

Returns:

The re-configured variant of the state backend

createCheckpointStorage

public CheckpointStorage createCheckpointStorage(JobID jobId)
                                          throws IOException

Description copied from interface: StateBackend

Creates a storage for checkpoints for the given job. The checkpoint storage is used to write checkpoint data and metadata.

Specified by:

createCheckpointStorage in interface StateBackend

Parameters:

jobId - The job to store checkpoint data for.

Returns:

A checkpoint storage for the given job.

Throws:

IOException - Thrown if the checkpoint storage cannot be initialized.

createOperatorStateBackend

public OperatorStateBackend createOperatorStateBackend(Environment env,
                                                       String operatorIdentifier)
                                                throws Exception

Description copied from interface: StateBackend

Creates a new OperatorStateBackend that can be used for storing operator state.

Operator state is state that is associated with parallel operator (or function) instances, rather than with keys.

Specified by:

createOperatorStateBackend in interface StateBackend

Specified by:

createOperatorStateBackend in class AbstractStateBackend

Parameters:

env - The runtime environment of the executing task.

operatorIdentifier - The identifier of the operator whose state should be stored.

Returns:

The OperatorStateBackend for operator identified by the job and operator identifier.

Throws:

Exception - This method may forward all exceptions that occur while instantiating the backend.

createKeyedStateBackend

public <K> AbstractKeyedStateBackend<K> createKeyedStateBackend(Environment env,
                                                                JobID jobID,
                                                                String operatorIdentifier,
                                                                TypeSerializer<K> keySerializer,
                                                                int numberOfKeyGroups,
                                                                KeyGroupRange keyGroupRange,
                                                                TaskKvStateRegistry kvStateRegistry,
                                                                TtlTimeProvider ttlTimeProvider)

Description copied from interface: StateBackend

Creates a new AbstractKeyedStateBackend that is responsible for holding keyed state and checkpointing it.

Keyed State is state where each value is bound to a key.

Specified by:

createKeyedStateBackend in interface StateBackend

Specified by:

createKeyedStateBackend in class AbstractStateBackend

Type Parameters:

K - The type of the keys by which the state is organized.

Returns:

The Keyed State Backend for the given job, operator, and key group range.

toString

public String toString()

Overrides:

toString in class Object