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本文主要研究一下flink的MemoryBackendCheckpointStorage
CheckpointStorage
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/CheckpointStorage.java
/**
* 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 {
boolean supportsHighlyAvailableStorage();
boolean hasDefaultSavepointLocation();
CompletedCheckpointStorageLocation resolveCheckpoint(String externalPointer) throws IOException;
CheckpointStorageLocation initializeLocationForCheckpoint(long checkpointId) throws IOException;
CheckpointStorageLocation initializeLocationForSavepoint(
long checkpointId,
@Nullable String externalLocationPointer) throws IOException;
CheckpointStreamFactory resolveCheckpointStorageLocation(
long checkpointId,
CheckpointStorageLocationReference reference) throws IOException;
CheckpointStateOutputStream createTaskOwnedStateStream() throws IOException;
}
- CheckpointStorage接口主要定义了持久化checkpoint data及metadata streams的基本方法；supportsHighlyAvailableStorage方法返回该backend是否支持highly available storage；hasDefaultSavepointLocation方法是否有默认的savepoint location；resolveCheckpoint方法用于解析checkpoint location返回CompletedCheckpointStorageLocation；initializeLocationForCheckpoint方法根据checkpointId来初始化storage location；initializeLocationForSavepoint方法用于根据checkpointId来初始化savepoint的storage location；resolveCheckpointStorageLocation方法解析CheckpointStorageLocationReference返回CheckpointStreamFactory；createTaskOwnedStateStream方法用于打开一个stream来持久化checkpoint state
AbstractFsCheckpointStorage
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/filesystem/AbstractFsCheckpointStorage.java
/**
* An implementation of durable checkpoint storage to file systems.
*/
public abstract class AbstractFsCheckpointStorage implements CheckpointStorage {
// ------------------------------------------------------------------------
// Constants
// ------------------------------------------------------------------------
/** The prefix of the directory containing the data exclusive to a checkpoint. */
public static final String CHECKPOINT_DIR_PREFIX = "chk-";
/** The name of the directory for shared checkpoint state. */
public static final String CHECKPOINT_SHARED_STATE_DIR = "shared";
/** The name of the directory for state not owned/released by the master, but by the TaskManagers. */
public static final String CHECKPOINT_TASK_OWNED_STATE_DIR = "taskowned";
/** The name of the metadata files in checkpoints / savepoints. */
public static final String METADATA_FILE_NAME = "_metadata";
/** The magic number that is put in front of any reference. */
private static final byte[] REFERENCE_MAGIC_NUMBER = new byte[] { 0x05, 0x5F, 0x3F, 0x18 };
// ------------------------------------------------------------------------
// Fields and properties
// ------------------------------------------------------------------------
/** The jobId, written into the generated savepoint directories. */
private final JobID jobId;
/** The default location for savepoints. Null, if none is configured. */
@Nullable
private final Path defaultSavepointDirectory;
@Override
public boolean hasDefaultSavepointLocation() {
return defaultSavepointDirectory != null;
}
@Override
public CompletedCheckpointStorageLocation resolveCheckpoint(String checkpointPointer) throws IOException {
return resolveCheckpointPointer(checkpointPointer);
}
/**
* Creates a file system based storage location for a savepoint.
*
* <p>This methods implements the logic that decides which location to use (given optional
* parameters for a configured location and a location passed for this specific savepoint)
* and how to name and initialize the savepoint directory.
*
* @param externalLocationPointer The target location pointer for the savepoint.
* Must be a valid URI. Null, if not supplied.
* @param checkpointId The checkpoint ID of the savepoint.
*
* @return The checkpoint storage location for the savepoint.
*
* @throws IOException Thrown if the target directory could not be created.
*/
@Override
public CheckpointStorageLocation initializeLocationForSavepoint(
@SuppressWarnings("unused") long checkpointId,
@Nullable String externalLocationPointer) throws IOException {
// determine where to write the savepoint to
final Path savepointBasePath;
if (externalLocationPointer != null) {
savepointBasePath = new Path(externalLocationPointer);
}
else if (defaultSavepointDirectory != null) {
savepointBasePath = defaultSavepointDirectory;
}
else {
throw new IllegalArgumentException("No savepoint location given and no default location configured.");
}
// generate the savepoint directory
final FileSystem fs = savepointBasePath.getFileSystem();
final String prefix = "savepoint-" + jobId.toString().substring(0, 6) + '-';
Exception latestException = null;
for (int attempt = 0; attempt < 10; attempt++) {
final Path path = new Path(savepointBasePath, FileUtils.getRandomFilename(prefix));
try {
if (fs.mkdirs(path)) {
// we make the path qualified, to make it independent of default schemes and authorities
final Path qp = path.makeQualified(fs);
return createSavepointLocation(fs, qp);
}
} catch (Exception e) {
latestException = e;
}
}
throw new IOException("Failed to create savepoint directory at " + savepointBasePath, latestException);
}
protected abstract CheckpointStorageLocation createSavepointLocation(FileSystem fs, Path location) throws IOException;
//......
}
- AbstractFsCheckpointStorage主要是实现了CheckpointStorage接口的hasDefaultSavepointLocation、resolveCheckpoint、initializeLocationForSavepoint方法
- resolveCheckpoint方法主要做两件事情，一个是解析checkpoint/savepoint path，一个是解析checkpoint/savepoint的metadata path，获取他们的FileStatus，然后创建FsCompletedCheckpointStorageLocation
- initializeLocationForSavepoint方法主要是给savepoint创建一个CheckpointStorageLocation，它可以根据externalLocationPointer来创建，该值为null的话则使用defaultSavepointDirectory，该方法里头调用了createSavepointLocation抽象方法，由子类去实现
MemoryBackendCheckpointStorage
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/memory/MemoryBackendCheckpointStorage.java
/**
* An implementation of a checkpoint storage for the {@link MemoryStateBackend}.
* Depending on whether this is created with a checkpoint location, the setup supports
* durable checkpoints (durable metadata) or not.
*/
public class MemoryBackendCheckpointStorage extends AbstractFsCheckpointStorage {
/** The target directory for checkpoints (here metadata files only). Null, if not configured. */
@Nullable
private final Path checkpointsDirectory;
/** The file system to persist the checkpoints to. Null if this does not durably persist checkpoints. */
@Nullable
private final FileSystem fileSystem;
/** The maximum size of state stored in a state handle. */
private final int maxStateSize;
/**
* Creates a new MemoryBackendCheckpointStorage.
*
* @param jobId The ID of the job writing the checkpoints.
* @param checkpointsBaseDirectory The directory to write checkpoints to. May be null,
* in which case this storage does not support durable persistence.
* @param defaultSavepointLocation The default savepoint directory, or null, if none is set.
* @param maxStateSize The maximum size of each individual piece of state.
*
* @throws IOException Thrown if a checkpoint base directory is given configured and the
* checkpoint directory cannot be created within that directory.
*/
public MemoryBackendCheckpointStorage(
JobID jobId,
@Nullable Path checkpointsBaseDirectory,
@Nullable Path defaultSavepointLocation,
int maxStateSize) throws IOException {
super(jobId, defaultSavepointLocation);
checkArgument(maxStateSize > 0);
this.maxStateSize = maxStateSize;
if (checkpointsBaseDirectory == null) {
checkpointsDirectory = null;
fileSystem = null;
}
else {
this.fileSystem = checkpointsBaseDirectory.getFileSystem();
this.checkpointsDirectory = getCheckpointDirectoryForJob(checkpointsBaseDirectory, jobId);
fileSystem.mkdirs(checkpointsDirectory);
}
}
// ------------------------------------------------------------------------
// Properties
// ------------------------------------------------------------------------
/**
* Gets the size (in bytes) that a individual chunk of state may have at most.
*/
public int getMaxStateSize() {
return maxStateSize;
}
// ------------------------------------------------------------------------
// Checkpoint Storage
// ------------------------------------------------------------------------
@Override
public boolean supportsHighlyAvailableStorage() {
return checkpointsDirectory != null;
}
@Override
public CheckpointStorageLocation initializeLocationForCheckpoint(long checkpointId) throws IOException {
checkArgument(checkpointId >= 0);
if (checkpointsDirectory != null) {
// configured for durable metadata
// prepare all the paths needed for the checkpoints
checkState(fileSystem != null);
final Path checkpointDir = createCheckpointDirectory(checkpointsDirectory, checkpointId);
// create the checkpoint exclusive directory
fileSystem.mkdirs(checkpointDir);
return new PersistentMetadataCheckpointStorageLocation(fileSystem, checkpointDir, maxStateSize);
}
else {
// no durable metadata - typical in IDE or test setup case
return new NonPersistentMetadataCheckpointStorageLocation(maxStateSize);
}
}
@Override
public CheckpointStreamFactory resolveCheckpointStorageLocation(
long checkpointId,
CheckpointStorageLocationReference reference) throws IOException {
// no matter where the checkpoint goes, we always return the storage location that stores
// state inline with the state handles.
return new MemCheckpointStreamFactory(maxStateSize);
}
@Override
public CheckpointStateOutputStream createTaskOwnedStateStream() throws IOException {
return new MemoryCheckpointOutputStream(maxStateSize);
}
@Override
protected CheckpointStorageLocation createSavepointLocation(FileSystem fs, Path location) throws IOException {
return new PersistentMetadataCheckpointStorageLocation(fs, location, maxStateSize);
}
// ------------------------------------------------------------------------
// Utilities
// ------------------------------------------------------------------------
@Override
public String toString() {
return "MemoryBackendCheckpointStorage {" +
"checkpointsDirectory=" + checkpointsDirectory +
", fileSystem=" + fileSystem +
", maxStateSize=" + maxStateSize +
'}';
}
}
- MemoryBackendCheckpointStorage继承了AbstractFsCheckpointStorage，实现了它定义的createSavepointLocation方法，这里返回的是PersistentMetadataCheckpointStorageLocation
- MemoryBackendCheckpointStorage还实现了CheckpointStorage接口定义的AbstractFsCheckpointStorage未实现的几个方法：supportsHighlyAvailableStorage、initializeLocationForCheckpoint、resolveCheckpointStorageLocation、createTaskOwnedStateStream
- supportsHighlyAvailableStorage是根据是否有配置checkpointsDirectory来判断；initializeLocationForCheckpoint这个根据checkpointsDirectory是否有设置来创建，为null的话，创建的是NonPersistentMetadataCheckpointStorageLocation，不为null创建的是PersistentMetadataCheckpointStorageLocation；resolveCheckpointStorageLocation这里创建的是MemCheckpointStreamFactory；而createTaskOwnedStateStream创建的是MemoryCheckpointOutputStream
小结
- CheckpointStorage接口主要定义了持久化checkpoint data及metadata streams的基本方法；AbstractFsCheckpointStorage主要是实现了CheckpointStorage接口的hasDefaultSavepointLocation、resolveCheckpoint、initializeLocationForSavepoint方法，同时定义了一个抽象方法createSavepointLocation
- MemoryBackendCheckpointStorage继承了AbstractFsCheckpointStorage，实现了它定义的createSavepointLocation方法，同时还实现了CheckpointStorage接口定义的AbstractFsCheckpointStorage未实现的几个方法：supportsHighlyAvailableStorage、initializeLocationForCheckpoint、resolveCheckpointStorageLocation、createTaskOwnedStateStream
- 这里可以看到MemoryBackendCheckpointStorage虽然是memory的，但是如果有配置checkpointsDirectory(
highly available storage)，checkpoint location使用的是PersistentMetadataCheckpointStorageLocation，否则使用NonPersistentMetadataCheckpointStorageLocation；而savepoint location使用的是PersistentMetadataCheckpointStorageLocation(checkpiont可以选择是否使用文件存储，而savepoint只能使用文件存储)
