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本文主要研究一下flink的MemCheckpointStreamFactory
CheckpointStreamFactory
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/CheckpointStreamFactory.java
/**
* A factory for checkpoint output streams, which are used to persist data for checkpoints.
*
* <p>Stream factories can be created from the {@link CheckpointStorage} through
* {@link CheckpointStorage#resolveCheckpointStorageLocation(long, CheckpointStorageLocationReference)}.
*/
public interface CheckpointStreamFactory {
CheckpointStateOutputStream createCheckpointStateOutputStream(CheckpointedStateScope scope) throws IOException;
abstract class CheckpointStateOutputStream extends FSDataOutputStream {
@Nullable
public abstract StreamStateHandle closeAndGetHandle() throws IOException;
@Override
public abstract void close() throws IOException;
}
}
CheckpointStreamFactory为checkpoint output streams(用于持久化checkpoint的数据)的工厂，它定义了createCheckpointStateOutputStream方法，这里返回的是CheckpointStateOutputStream；CheckpointStateOutputStream继承了FSDataOutputStream，它定义了closeAndGetHandle及close两个抽象方法
CheckpointStreamFactory有两个以factory命名的实现类，分别是MemCheckpointStreamFactory(它有两个子类分别为NonPersistentMetadataCheckpointStorageLocation、PersistentMetadataCheckpointStorageLocation)、FsCheckpointStreamFactory(它有一个子类为FsCheckpointStorageLocation)
CheckpointStorageLocation接口继承了CheckpointStreamFactory接口，它有三个实现类，分别是NonPersistentMetadataCheckpointStorageLocation、PersistentMetadataCheckpointStorageLocation、FsCheckpointStorageLocation
FSDataOutputStream
flink-core-1.7.0-sources.jar!/org/apache/flink/core/fs/FSDataOutputStream.java
@Public
public abstract class FSDataOutputStream extends OutputStream {
public abstract long getPos() throws IOException;
public abstract void flush() throws IOException;
public abstract void sync() throws IOException;
public abstract void close() throws IOException;
}
FSDataOutputStream继承了java的OutputStream，它多定义了getPos、flush、sync、close几个抽象方法
CheckpointStorageLocation
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/CheckpointStorageLocation.java
/**
* A storage location for one particular checkpoint, offering data persistent, metadata persistence,
* and lifecycle/cleanup methods.
*
* <p>CheckpointStorageLocations are typically created and initialized via
* {@link CheckpointStorage#initializeLocationForCheckpoint(long)} or
* {@link CheckpointStorage#initializeLocationForSavepoint(long, String)}.
*/
public interface CheckpointStorageLocation extends CheckpointStreamFactory {
CheckpointMetadataOutputStream createMetadataOutputStream() throws IOException;
void disposeOnFailure() throws IOException;
CheckpointStorageLocationReference getLocationReference();
}
CheckpointStorageLocation继承了CheckpointStreamFactory接口，它通常是由CheckpointStorage来创建及初始化，提供数据持久化、metadata存储及lifecycle/cleanup相关方法；这里定义了createMetadataOutputStream方法用来创建CheckpointMetadataOutputStream；disposeOnFailure方法用于在checkpoint失败的时候dispose checkpoint location；getLocationReference用于返回CheckpointStorageLocationReference
MemCheckpointStreamFactory
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/memory/MemCheckpointStreamFactory.java
/**
* {@link CheckpointStreamFactory} that produces streams that write to in-memory byte arrays.
*/
public class MemCheckpointStreamFactory implements CheckpointStreamFactory {
/** The maximal size that the snapshotted memory state may have */
private final int maxStateSize;
/**
* Creates a new in-memory stream factory that accepts states whose serialized forms are
* up to the given number of bytes.
*
* @param maxStateSize The maximal size of the serialized state
*/
public MemCheckpointStreamFactory(int maxStateSize) {
this.maxStateSize = maxStateSize;
}
@Override
public CheckpointStateOutputStream createCheckpointStateOutputStream(
CheckpointedStateScope scope) throws IOException
{
return new MemoryCheckpointOutputStream(maxStateSize);
}
@Override
public String toString() {
return “In-Memory Stream Factory”;
}
static void checkSize(int size, int maxSize) throws IOException {
if (size > maxSize) {
throw new IOException(
“Size of the state is larger than the maximum permitted memory-backed state. Size=”
+ size + ” , maxSize=” + maxSize
+ ” . Consider using a different state backend, like the File System State backend.”);
}
}
/**
* A {@code CheckpointStateOutputStream} that writes into a byte array.
*/
public static class MemoryCheckpointOutputStream extends CheckpointStateOutputStream {
private final ByteArrayOutputStreamWithPos os = new ByteArrayOutputStreamWithPos();
private final int maxSize;
private AtomicBoolean closed;
boolean isEmpty = true;
public MemoryCheckpointOutputStream(int maxSize) {
this.maxSize = maxSize;
this.closed = new AtomicBoolean(false);
}
@Override
public void write(int b) throws IOException {
os.write(b);
isEmpty = false;
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
os.write(b, off, len);
isEmpty = false;
}
@Override
public void flush() throws IOException {
os.flush();
}
@Override
public void sync() throws IOException { }
// ——————————————————————–
@Override
public void close() {
if (closed.compareAndSet(false, true)) {
closeInternal();
}
}
@Nullable
@Override
public StreamStateHandle closeAndGetHandle() throws IOException {
if (isEmpty) {
return null;
}
return new ByteStreamStateHandle(String.valueOf(UUID.randomUUID()), closeAndGetBytes());
}
@Override
public long getPos() throws IOException {
return os.getPosition();
}
public boolean isClosed() {
return closed.get();
}
/**
* Closes the stream and returns the byte array containing the stream’s data.
* @return The byte array containing the stream’s data.
* @throws IOException Thrown if the size of the data exceeds the maximal
*/
public byte[] closeAndGetBytes() throws IOException {
if (closed.compareAndSet(false, true)) {
checkSize(os.size(), maxSize);
byte[] bytes = os.toByteArray();
closeInternal();
return bytes;
} else {
throw new IOException(“stream has already been closed”);
}
}
private void closeInternal() {
os.reset();
}
}
}
MemCheckpointStreamFactory实现了CheckpointStreamFactory接口，这里createCheckpointStateOutputStream方法返回MemoryCheckpointOutputStream
MemoryCheckpointOutputStream继承了CheckpointStateOutputStream，里头使用了ByteArrayOutputStreamWithPos，它在closeAndGetHandle的时候会校验大小是否超过maxSize的限制，超出则抛出IOException异常
MemCheckpointStreamFactory有两个子类分别为NonPersistentMetadataCheckpointStorageLocation、PersistentMetadataCheckpointStorageLocation，它们都实现了CheckpointStorageLocation接口
NonPersistentMetadataCheckpointStorageLocation
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/memory/NonPersistentMetadataCheckpointStorageLocation.java
/**
* A checkpoint storage location for the {@link MemoryStateBackend} in case no durable persistence
* for metadata has been configured.
*/
public class NonPersistentMetadataCheckpointStorageLocation
extends MemCheckpointStreamFactory
implements CheckpointStorageLocation {
/** The external pointer returned for checkpoints that are not externally addressable. */
public static final String EXTERNAL_POINTER = “<checkpoint-not-externally-addressable>”;
public NonPersistentMetadataCheckpointStorageLocation(int maxStateSize) {
super(maxStateSize);
}
@Override
public CheckpointMetadataOutputStream createMetadataOutputStream() throws IOException {
return new MetadataOutputStream();
}
@Override
public void disposeOnFailure() {}
@Override
public CheckpointStorageLocationReference getLocationReference() {
return CheckpointStorageLocationReference.getDefault();
}
// ————————————————————————
// CompletedCheckpointStorageLocation
// ————————————————————————
/**
* A {@link CompletedCheckpointStorageLocation} that is not persistent and only holds the
* metadata in an internal byte array.
*/
private static class NonPersistentCompletedCheckpointStorageLocation implements CompletedCheckpointStorageLocation {
private static final long serialVersionUID = 1L;
private final ByteStreamStateHandle metaDataHandle;
NonPersistentCompletedCheckpointStorageLocation(ByteStreamStateHandle metaDataHandle) {
this.metaDataHandle = metaDataHandle;
}
@Override
public String getExternalPointer() {
return EXTERNAL_POINTER;
}
@Override
public StreamStateHandle getMetadataHandle() {
return metaDataHandle;
}
@Override
public void disposeStorageLocation() {}
}
// ————————————————————————
// CheckpointMetadataOutputStream
// ————————————————————————
private static class MetadataOutputStream extends CheckpointMetadataOutputStream {
private final ByteArrayOutputStreamWithPos os = new ByteArrayOutputStreamWithPos();
private boolean closed;
@Override
public void write(int b) throws IOException {
os.write(b);
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
os.write(b, off, len);
}
@Override
public void flush() throws IOException {
os.flush();
}
@Override
public long getPos() throws IOException {
return os.getPosition();
}
@Override
public void sync() throws IOException { }
@Override
public CompletedCheckpointStorageLocation closeAndFinalizeCheckpoint() throws IOException {
synchronized (this) {
if (!closed) {
closed = true;
byte[] bytes = os.toByteArray();
ByteStreamStateHandle handle = new ByteStreamStateHandle(UUID.randomUUID().toString(), bytes);
return new NonPersistentCompletedCheckpointStorageLocation(handle);
} else {
throw new IOException(“Already closed”);
}
}
}
@Override
public void close() {
if (!closed) {
closed = true;
os.reset();
}
}
}
}
MemoryBackendCheckpointStorage在没有配置checkpointsDirectory的时候创建的是NonPersistentMetadataCheckpointStorageLocation；其createMetadataOutputStream方法创建的是MetadataOutputStream
MetadataOutputStream继承了CheckpointMetadataOutputStream，里头使用的是ByteArrayOutputStreamWithPos，而closeAndFinalizeCheckpoint返回的是NonPersistentCompletedCheckpointStorageLocation
NonPersistentCompletedCheckpointStorageLocation实现了CompletedCheckpointStorageLocation接口，其getMetadataHandle方法返回的是ByteStreamStateHandle
PersistentMetadataCheckpointStorageLocation
flink-runtime_2.11-1.7.0-sources.jar!/org/apache/flink/runtime/state/memory/PersistentMetadataCheckpointStorageLocation.java
/**
* A checkpoint storage location for the {@link MemoryStateBackend} when it durably
* persists the metadata in a file system.
*/
public class PersistentMetadataCheckpointStorageLocation
extends MemCheckpointStreamFactory
implements CheckpointStorageLocation {
private final FileSystem fileSystem;
private final Path checkpointDirectory;
private final Path metadataFilePath;
/**
* Creates a checkpoint storage persists metadata to a file system and stores state
* in line in state handles with the metadata.
*
* @param fileSystem The file system to which the metadata will be written.
* @param checkpointDir The directory where the checkpoint metadata will be written.
*/
public PersistentMetadataCheckpointStorageLocation(
FileSystem fileSystem,
Path checkpointDir,
int maxStateSize) {
super(maxStateSize);
this.fileSystem = checkNotNull(fileSystem);
this.checkpointDirectory = checkNotNull(checkpointDir);
this.metadataFilePath = new Path(checkpointDir, AbstractFsCheckpointStorage.METADATA_FILE_NAME);
}
// ————————————————————————
@Override
public CheckpointMetadataOutputStream createMetadataOutputStream() throws IOException {
return new FsCheckpointMetadataOutputStream(fileSystem, metadataFilePath, checkpointDirectory);
}
@Override
public void disposeOnFailure() throws IOException {
// on a failure, no chunk in the checkpoint directory needs to be saved, so
// we can drop it as a whole
fileSystem.delete(checkpointDirectory, true);
}
@Override
public CheckpointStorageLocationReference getLocationReference() {
return CheckpointStorageLocationReference.getDefault();
}
}
MemoryBackendCheckpointStorage在配置了checkpointsDirectory的时候创建的是PersistentMetadataCheckpointStorageLocation；其createMetadataOutputStream方法创建的是FsCheckpointMetadataOutputStream；FsCheckpointMetadataOutputStream的构造器接收三个参数，分别是fileSystem、metadataFilePath、exclusiveCheckpointDir；其中fileSystem用于根据metadataFilePath来创建FSDataOutputStream，而exclusiveCheckpointDir则在返回FsCompletedCheckpointStorageLocation的时候用到
小结
MemoryBackendCheckpointStorage在没有配置checkpointsDirectory的时候创建的是NonPersistentMetadataCheckpointStorageLocation；在配置了checkpointsDirectory的时候创建的是PersistentMetadataCheckpointStorageLocation
NonPersistentMetadataCheckpointStorageLocation及PersistentMetadataCheckpointStorageLocation都继承了MemCheckpointStreamFactory类，同时实现了CheckpointStorageLocation接口(其createMetadataOutputStream方法返回的CheckpointMetadataOutputStream类型分别为MetadataOutputStream、FsCheckpointMetadataOutputStream)
MemCheckpointStreamFactory实现了CheckpointStreamFactory接口，它的createCheckpointStateOutputStream方法返回MemoryCheckpointOutputStream；CheckpointStorageLocation继承了CheckpointStreamFactory接口，它通常是由CheckpointStorage来创建及初始化，提供数据持久化、metadata存储及lifecycle/cleanup相关方法
doc
The MemoryStateBackend
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