Implement BeamFileSystemClient for Delta Lake connector#38873
Implement BeamFileSystemClient for Delta Lake connector#38873joaohmalves wants to merge 4 commits into
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Summary of ChangesHello, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request implements the Delta Kernel Engine's FileSystemClient interface using Apache Beam's native FileSystems API. This change provides the necessary abstraction for the Delta Lake connector to perform metadata log operations across various storage layers supported by Beam, such as GCS, S3, and HDFS. The integration ensures that the Delta Lake connector can operate seamlessly within the Beam ecosystem by delegating filesystem lifecycle and I/O operations to Beam's robust infrastructure. Highlights
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joaohmalves
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Code Review
This pull request introduces BeamFileSystemClient, a Delta Kernel FileSystemClient implementation backed by Apache Beam's FileSystems. It integrates this client into BeamEngine and updates various DoFns and tests to use it. The review feedback identifies two critical issues in BeamFileSystemClient: an unused normalizedInput variable in listFrom that should be used to ensure consistent path normalization (along with filtering out directories), and the use of Java 9+ and Java 12+ APIs (InputStream.readNBytes and skipNBytes) which will cause runtime errors on Java 8/11 environments. Replacing these with Guava's ByteStreams is recommended.
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| for (MatchResult.Metadata metadata : | ||
| FileSystems.match(glob, EmptyMatchTreatment.ALLOW).metadata()) { | ||
| String metadataPath = metadata.resourceId().toString(); | ||
| if (normalizeForOrdering(metadataPath).compareTo(normalizeForOrdering(path)) >= 0) { | ||
| statuses.add(toDeltaFileStatus(metadata)); | ||
| } | ||
| } |
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The normalizedInput variable is defined on line 55 but never used. Instead, the raw path parameter is used in the comparison on line 60. This can lead to incorrect filtering in listFrom if the input path and the matched metadata paths have different normalization formats (e.g., file:/ vs file:///).
Additionally, listFrom should filter out directories to prevent downstream components from attempting to read directories as files. We can achieve this by checking !metadata.resourceId().isDirectory().
for (MatchResult.Metadata metadata :
FileSystems.match(glob, EmptyMatchTreatment.ALLOW).metadata()) {
if (metadata.resourceId().isDirectory()) {
continue;
}
String metadataPath = metadata.resourceId().toString();
if (normalizeForOrdering(metadataPath).compareTo(normalizeForOrdering(normalizedInput)) >= 0) {
statuses.add(toDeltaFileStatus(metadata));
}
}| } else { | ||
| try (InputStream stream = Channels.newInputStream(channel)) { | ||
| stream.skipNBytes(startOffset); | ||
| int read = stream.readNBytes(data, 0, readLength); | ||
| if (read != readLength) { | ||
| throw new EOFException( | ||
| String.format("Expected %s bytes from %s but read %s", readLength, path, read)); | ||
| } | ||
| } | ||
| } |
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The methods InputStream.skipNBytes (introduced in Java 12) and InputStream.readNBytes (introduced in Java 9) are used here. Since Apache Beam supports Java 8 and Java 11 as target runtimes, using these Java 12+ APIs will cause NoSuchMethodError at runtime on those platforms.
We can use Guava's ByteStreams.skipFully and ByteStreams.readFully instead, which are fully compatible with Java 8/11 and are already available on the classpath.
} else {
try (InputStream stream = Channels.newInputStream(channel)) {
com.google.common.io.ByteStreams.skipFully(stream, startOffset);
com.google.common.io.ByteStreams.readFully(stream, data);
}
}
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Implements the Delta Kernel Engine FileSystemClient interface backed by Apache Beam's native FileSystems API. This provides the foundational abstraction required for the Delta Lake conector to read/write metadata logs across any Beam-supported storage layer (GCS, S3, HDFS, local files, etc.).
What changes
sdks/java/io/.../BeamFileSystemClient.java: Implements FileSystemClient. Implements listFrom using FileSystems.match with lexicographical sorting; maps readFiles to sequential bounded array stream reads; delegates delete and copyFileAtomically using Beam's native lifecycle options (IGNORE_MISSING_FILES, SKIP_IF_DESTINATION_EXISTS).
sdks/java/io/.../BeamEngine.java: Hooks up BeamFileSystemClient as the default system client instance inside the engine constructors.
sdks/java/io/.../BeamFileSystemClientTest.java: Unit tests covering filesystem operations, range reads, folder behavior, and ordering logic using JUnit TemporaryFolder.
Fixes #38554.
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