galenwarren opened a new pull request #14875:
URL: https://github.com/apache/flink/pull/14875
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## What is the purpose of the change
Add a FileSystem implementation with associated RecoverableWriter
implementation for Google Cloud Storage, in order to be able to write to GCS
via a StreamingFileSink.
## Brief change log
- Add GSFileSystemFactory and register with SPI under
org.apache.flink.core.fs.FileSystemFactory. This factory supports the ```gs```
scheme.
- GSFileSystemFactory creates instances of GSFileSystem, which extends
HadoopFileSystem. An instance of [GoogleHadoopFileSystem
](https://github.com/GoogleCloudDataproc/hadoop-connectors/blob/master/gcs/src/main/java/com/google/cloud/hadoop/fs/gcs/GoogleHadoopFileSystem.java)
(i.e. the standard Hadoop connector for GCS) is used to construct
HadoopFileSystem.
- GSFileSystem creates instances of GSRecoverableWriter via
```createRecoverableWriter```
- GSRecoverableWriter writes files to GCS in a two-step process, by first
writing to a temporary blob, using the [resumable
upload](https://cloud.google.com/storage/docs/resumable-uploads) feature, and
then copying the temp blob to the final blob on commit (and deleting the temp
file). Resumable uploads can be active for up to one week.
- Recoverability during the resumable upload process is provided by the
```capture``` method on
[WriteChannel](https://googleapis.dev/java/google-cloud-clients/0.90.0-alpha/com/google/cloud/WriteChannel.html)
and the ```restore``` method on
[RestorableState<WriteChannel>](https://googleapis.dev/java/google-cloud-clients/0.90.0-alpha/com/google/cloud/RestorableState.html).
GSRecoverable holds the recoverable state, which includes:
- The opaque RestorableState object returned from
[WriteChannel.capture](https://googleapis.dev/java/google-cloud-clients/0.90.0-alpha/com/google/cloud/WriteChannel.html#capture--)
(which is Java serializable)
- The position in the write stream
- The "plan", i.e. an instance of GSRecoverablePlan, which includes the
temporary and final blob ids, to be used for eventual commit or cleanup
Four new Flink options are added:
- **gs.upload.content.type**. This is the content type to use when writing
blobs. Default: ```application/octet-stream```.
- **gs.upload.temp.bucket**. The bucket to use for temporary blobs. There is
no default; if unspecified, temporary blobs are written to the same bucket as
the final blobs. Specifying this option would allow one to put temporary blobs
in their own bucket.
- **gs.upload.temp.prefix**. The prefix to apply to the final object name to
generate the temporary object name. A UUID string is also appended to the
temporary object name to avoid collisions during the resumable upload process.
Default value: ```.inprogress```
- **gs.upload.chunk.size**. The chunk size to set for uploads. If zero (the
default), no chunk size is set and the Google default value is used.
So, for example -- if a write were initiated to
```gs://bucket-name/foo/bar```, the following would happen (assuming default
values for the options above):
- A temporary blob would be created at, say,
```gs://bucket-name/.inprogress/foo/bar/e202b566-150f-4784-9025-136cf351fcfe```
- Writes would be performed against this blob via resumable upload for up to
a week, with support for saving and restoring the upload state
- Upon commit, the temporary blob would be copied to
```gs://bucket-name/foo/bar``` and the temporary blob would be deleted
- Upon failure, the temporary blob would be deleted (via
[RecoverableWriter.cleanupRecoverableState](https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/core/fs/RecoverableWriter.html#cleanupRecoverableState-org.apache.flink.core.fs.RecoverableWriter.ResumeRecoverable-))
A few important implementation notes:
- The GSRecoverableWriterHelper class and its child interfaces -- Storage,
Writer, and WriterState -- abstract away the interactions with the underlying
GCS interfaces. DefaultGSRecoverableWriterHelper implements
GSRecoverableWriterHelper against the underlying GCS interfaces; for
unit-testing purposes, MockGSRecoverableWriterHelper implements
GSRecoverableWriterHelper against in-memory objects.
- GSRecoverableWriterHelper.WriterState implements Serializable, as it wraps
an instance of the opaque
[RestorableState<WriteChannel>](https://googleapis.dev/java/google-cloud-clients/0.90.0-alpha/com/google/cloud/RestorableState.html)
returned from the GCS API. RestorableState instances are required to be Java
serializable, and this would seem to be the only way to serialize/deserialze
them. **So, GSRecoverableSerializer uses Java serialization for WriteState**.
I'm aware this goes against the guidance not to use Java serialization, but, in
this case, I don't see an alternative (but I'm open to suggestions).
## Verifying this change
*(Please pick either of the following options)*
This change is a trivial rework / code cleanup without any test coverage.
*(or)*
This change is already covered by existing tests, such as *(please describe
tests)*.
*(or)*
**This change added tests and can be verified as follows**:
- Added unit tests in GSFileSystem test to verify the proper function of
GSFileSystemFactory and GSFileSystem, including Flink options and passthrough
of options to Hadoop. No validation of the external
[GoogleHadoopFileSystem](https://github.com/GoogleCloudDataproc/hadoop-connectors/blob/master/gcs/src/main/java/com/google/cloud/hadoop/fs/gcs/GoogleHadoopFileSystem.java)
is performed.
- Added unit tests in GSRecoverableWriterTest to test scenarios related to
writing, persist/restore, and cleanup.
- Added unit tests in GSRecoverableSerializerTest to test serialization of
GSRecoverable.
- Added unit tests in GSRecoverableCommitterTest to test commit scenarios,
including commit after recovery.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): (**yes** / no)
- Adds a new project -- **flink-gs-fs-hadoop** -- which includes
dependencies
[google-cloud-storage](https://mvnrepository.com/artifact/com.google.cloud/google-cloud-storage)
and
[gcs-connector](https://mvnrepository.com/artifact/com.google.cloud.bigdataoss/gcs-connector).
I have a question about the proper scope for gcs-connector which I'll ask in a
follow-up comment.
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: (yes / **no**)
- The serializers: (**yes** / no / don't know)
- Adds GSRecoverableSerializer, to serialize instances of GSRecoverable
- The runtime per-record code paths (performance sensitive): (yes / **no**
/ don't know)
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (yes / **no** /
don't know)
- The S3 file system connector: (yes / **no** / don't know)
## Documentation
- Does this pull request introduce a new feature? (**yes** / no)
- If yes, how is the feature documented? (not applicable / **docs** /
**JavaDocs** / not documented)
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