聊聊flink的BlobStoreService

序

本文主要研究一下flink的BlobStoreService

BlobView

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/blob/BlobView.java

public interface BlobView {

	/**
	 * Copies a blob to a local file.
	 *
	 * @param jobId     ID of the job this blob belongs to (or <tt>null</tt> if job-unrelated)
	 * @param blobKey   The blob ID
	 * @param localFile The local file to copy to
	 *
	 * @return whether the file was copied (<tt>true</tt>) or not (<tt>false</tt>)
	 * @throws IOException If the copy fails
	 */
	boolean get(JobID jobId, BlobKey blobKey, File localFile) throws IOException;
}
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• BlobView定义了get方法，将指定的blob拷贝到localFile

BlobStore

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/blob/BlobStore.java

public interface BlobStore extends BlobView {

	/**
	 * Copies the local file to the blob store.
	 *
	 * @param localFile The file to copy
	 * @param jobId ID of the job this blob belongs to (or <tt>null</tt> if job-unrelated)
	 * @param blobKey   The ID for the file in the blob store
	 *
	 * @return whether the file was copied (<tt>true</tt>) or not (<tt>false</tt>)
	 * @throws IOException If the copy fails
	 */
	boolean put(File localFile, JobID jobId, BlobKey blobKey) throws IOException;

	/**
	 * Tries to delete a blob from storage.
	 *
	 * <p>NOTE: This also tries to delete any created directories if empty.</p>
	 *
	 * @param jobId ID of the job this blob belongs to (or <tt>null</tt> if job-unrelated)
	 * @param blobKey The blob ID
	 *
	 * @return  <tt>true</tt> if the given blob is successfully deleted or non-existing;
	 *          <tt>false</tt> otherwise
	 */
	boolean delete(JobID jobId, BlobKey blobKey);

	/**
	 * Tries to delete all blobs for the given job from storage.
	 *
	 * <p>NOTE: This also tries to delete any created directories if empty.</p>
	 *
	 * @param jobId The JobID part of all blobs to delete
	 *
	 * @return  <tt>true</tt> if the job directory is successfully deleted or non-existing;
	 *          <tt>false</tt> otherwise
	 */
	boolean deleteAll(JobID jobId);
}
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• BlobStore继承了BlobView，它定义了put、delete、deleteAll方法

BlobStoreService

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/blob/BlobStoreService.java

public interface BlobStoreService extends BlobStore, Closeable {

	/**
	 * Closes and cleans up the store. This entails the deletion of all blobs.
	 */
	void closeAndCleanupAllData();
}
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• BlobStoreService继承了BlobStore及Closeable接口，它定义了closeAndCleanupAllData方法；它有两个实现类，分别是VoidBlobStore、FileSystemBlobStore

VoidBlobStore

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/blob/VoidBlobStore.java

public class VoidBlobStore implements BlobStoreService {

	@Override
	public boolean put(File localFile, JobID jobId, BlobKey blobKey) throws IOException {
		return false;
	}

	@Override
	public boolean get(JobID jobId, BlobKey blobKey, File localFile) throws IOException {
		return false;
	}

	@Override
	public boolean delete(JobID jobId, BlobKey blobKey) {
		return true;
	}

	@Override
	public boolean deleteAll(JobID jobId) {
		return true;
	}

	@Override
	public void closeAndCleanupAllData() {}

	@Override
	public void close() throws IOException {}
}
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• VoidBlobStore实现了BlobStoreService接口，它执行空操作

FileSystemBlobStore

flink-release-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/blob/FileSystemBlobStore.java

public class FileSystemBlobStore implements BlobStoreService {

	private static final Logger LOG = LoggerFactory.getLogger(FileSystemBlobStore.class);

	/** The file system in which blobs are stored. */
	private final FileSystem fileSystem;

	/** The base path of the blob store. */
	private final String basePath;

	public FileSystemBlobStore(FileSystem fileSystem, String storagePath) throws IOException {
		this.fileSystem = checkNotNull(fileSystem);
		this.basePath = checkNotNull(storagePath) + "/blob";

		LOG.info("Creating highly available BLOB storage directory at {}", basePath);

		fileSystem.mkdirs(new Path(basePath));
		LOG.debug("Created highly available BLOB storage directory at {}", basePath);
	}

	// - Put ------------------------------------------------------------------

	@Override
	public boolean put(File localFile, JobID jobId, BlobKey blobKey) throws IOException {
		return put(localFile, BlobUtils.getStorageLocationPath(basePath, jobId, blobKey));
	}

	private boolean put(File fromFile, String toBlobPath) throws IOException {
		try (OutputStream os = fileSystem.create(new Path(toBlobPath), FileSystem.WriteMode.OVERWRITE)) {
			LOG.debug("Copying from {} to {}.", fromFile, toBlobPath);
			Files.copy(fromFile, os);
		}
		return true;
	}

	// - Get ------------------------------------------------------------------

	@Override
	public boolean get(JobID jobId, BlobKey blobKey, File localFile) throws IOException {
		return get(BlobUtils.getStorageLocationPath(basePath, jobId, blobKey), localFile, blobKey);
	}

	private boolean get(String fromBlobPath, File toFile, BlobKey blobKey) throws IOException {
		checkNotNull(fromBlobPath, "Blob path");
		checkNotNull(toFile, "File");
		checkNotNull(blobKey, "Blob key");

		if (!toFile.exists() && !toFile.createNewFile()) {
			throw new IOException("Failed to create target file to copy to");
		}

		final Path fromPath = new Path(fromBlobPath);
		MessageDigest md = BlobUtils.createMessageDigest();

		final int buffSize = 4096; // like IOUtils#BLOCKSIZE, for chunked file copying

		boolean success = false;
		try (InputStream is = fileSystem.open(fromPath);
			FileOutputStream fos = new FileOutputStream(toFile)) {
			LOG.debug("Copying from {} to {}.", fromBlobPath, toFile);

			// not using IOUtils.copyBytes(is, fos) here to be able to create a hash on-the-fly
			final byte[] buf = new byte[buffSize];
			int bytesRead = is.read(buf);
			while (bytesRead >= 0) {
				fos.write(buf, 0, bytesRead);
				md.update(buf, 0, bytesRead);

				bytesRead = is.read(buf);
			}

			// verify that file contents are correct
			final byte[] computedKey = md.digest();
			if (!Arrays.equals(computedKey, blobKey.getHash())) {
				throw new IOException("Detected data corruption during transfer");
			}

			success = true;
		} finally {
			// if the copy fails, we need to remove the target file because
			// outside code relies on a correct file as long as it exists
			if (!success) {
				try {
					toFile.delete();
				} catch (Throwable ignored) {}
			}
		}

		return true; // success is always true here
	}

	// - Delete ---------------------------------------------------------------

	@Override
	public boolean delete(JobID jobId, BlobKey blobKey) {
		return delete(BlobUtils.getStorageLocationPath(basePath, jobId, blobKey));
	}

	@Override
	public boolean deleteAll(JobID jobId) {
		return delete(BlobUtils.getStorageLocationPath(basePath, jobId));
	}

	private boolean delete(String blobPath) {
		try {
			LOG.debug("Deleting {}.", blobPath);

			Path path = new Path(blobPath);

			boolean result = fileSystem.delete(path, true);

			// send a call to delete the directory containing the file. This will
			// fail (and be ignored) when some files still exist.
			try {
				fileSystem.delete(path.getParent(), false);
				fileSystem.delete(new Path(basePath), false);
			} catch (IOException ignored) {}
			return result;
		}
		catch (Exception e) {
			LOG.warn("Failed to delete blob at " + blobPath);
			return false;
		}
	}

	@Override
	public void closeAndCleanupAllData() {
		try {
			LOG.debug("Cleaning up {}.", basePath);

			fileSystem.delete(new Path(basePath), true);
		}
		catch (Exception e) {
			LOG.error("Failed to clean up recovery directory.", e);
		}
	}

	@Override
	public void close() throws IOException {
		// nothing to do for the FileSystemBlobStore
	}
}
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• FileSystemBlobStore实现了BlobStoreService，它的构造器要求传入fileSystem及storagePath；put方法通过fileSystem.create来创建目标OutputStream，然后通过Files.copy把localFile拷贝到toBlobPath；get方法通过fileSystem.open打开要读取的blob，然后写入到localFile；delete及deleteAll方法通过BlobUtils.getStorageLocationPath获取blobPath，然后调用fileSystem.delete来删除；closeAndCleanupAllData方法直接调用fileSystem.delete来递归删除整个storagePath

小结

• BlobView定义了get方法，将指定的blob拷贝到localFile；BlobStore继承了BlobView，它定义了put、delete、deleteAll方法
• BlobStoreService继承了BlobStore及Closeable接口，它定义了closeAndCleanupAllData方法；它有两个实现类，分别是VoidBlobStore、FileSystemBlobStore
• VoidBlobStore实现了BlobStoreService接口，它执行空操作；FileSystemBlobStore实现了BlobStoreService，它的构造器要求传入fileSystem及storagePath；put方法通过fileSystem.create来创建目标OutputStream，然后通过Files.copy把localFile拷贝到toBlobPath；get方法通过fileSystem.open打开要读取的blob，然后写入到localFile；delete及deleteAll方法通过BlobUtils.getStorageLocationPath获取blobPath，然后调用fileSystem.delete来删除；closeAndCleanupAllData方法直接调用fileSystem.delete来递归删除整个storagePath

doc

• BlobStoreService