aljoscha closed pull request #6532: [FLINK-10109] Add documentation for StreamingFileSink URL: https://github.com/apache/flink/pull/6532
This is a PR merged from a forked repository. As GitHub hides the original diff on merge, it is displayed below for the sake of provenance: As this is a foreign pull request (from a fork), the diff is supplied below (as it won't show otherwise due to GitHub magic): diff --git a/docs/dev/connectors/streamfile_sink.md b/docs/dev/connectors/streamfile_sink.md new file mode 100644 index 00000000000..3db5577f67c --- /dev/null +++ b/docs/dev/connectors/streamfile_sink.md @@ -0,0 +1,123 @@ +--- +title: "Streaming File Sink" +nav-title: Streaming File Sink +nav-parent_id: connectors +nav-pos: 5 +--- +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> + +This connector provides a Sink that writes partitioned files to filesystems +supported by the Flink `FileSystem` abstraction. Since in streaming the input +is potentially infinite, the streaming file sink writes data into buckets. The +bucketing behaviour is configurable but a useful default is time-based +bucketing where we start writing a new bucket every hour and thus get +individual files that each contain a part of the infinite output stream. + +Within a bucket, we further split the output into smaller part files based on a +rolling policy. This is useful to prevent individual bucket files from getting +too big. This is also configurable but the default policy rolls files based on +file size and a timeout, i.e if no new data was written to a part file. + +The `StreamingFileSink` supports both row-wise encoding formats and +bulk-encoding formats, such as [Apache Parquet](http://parquet.apache.org). + +#### Using Row-encoded Output Formats + +The only required configuration are the base path where we want to output our +data and an +[Encoder]({{ site.baseurl }}/api/java/org/apache/flink/api/common/serialization/Encoder.html) +that is used for serializing records to the `OutputStream` for each file. + +Basic usage thus looks like this: + + +<div class="codetabs" markdown="1"> +<div data-lang="java" markdown="1"> +{% highlight java %} +import org.apache.flink.api.common.serialization.Encoder; +import org.apache.flink.core.fs.Path; +import org.apache.flink.streaming.api.functions.sink.filesystem.StreamingFileSink; + +DataStream<String> input = ...; + +final StreamingFileSink<String> sink = StreamingFileSink + .forRowFormat(new Path(outputPath), (Encoder<String>) (element, stream) -> { + PrintStream out = new PrintStream(stream); + out.println(element.f1); + }) + .build(); + +input.addSink(sink); + +{% endhighlight %} +</div> +<div data-lang="scala" markdown="1"> +{% highlight scala %} +import org.apache.flink.api.common.serialization.Encoder +import org.apache.flink.core.fs.Path +import org.apache.flink.streaming.api.functions.sink.filesystem.StreamingFileSink + +val input: DataStream[String] = ... + +final StreamingFileSink[String] sink = StreamingFileSink + .forRowFormat(new Path(outputPath), (element, stream) => { + val out = new PrintStream(stream) + out.println(element.f1) + }) + .build() + +input.addSink(sink) + +{% endhighlight %} +</div> +</div> + +This will create a streaming sink that creates hourly buckets and uses a +default rolling policy. The default bucket assigner is +[DateTimeBucketAssigner]({{ site.baseurl }}/api/java/org/apache/flink/streaming/api/functions/sink/filesystem/bucketassigners/DateTimeBucketAssigner.html) +and the default rolling policy is +[DefaultRollingPolicy]({{ site.baseurl }}/api/java/org/apache/flink/streaming/api/functions/sink/filesystem/rollingpolicies/DefaultRollingPolicy.html). +You can specify a custom +[BucketAssigner]({{ site.baseurl }}/api/java/org/apache/flink/streaming/api/functions/sink/filesystem/BucketAssigner.html) +and +[RollingPolicy]({{ site.baseurl }}/api/java/org/apache/flink/streaming/api/functions/sink/filesystem/RollingPolicy.html) +on the sink builder. Please check out the JavaDoc for +[StreamingFileSink]({{ site.baseurl }}/api/java/org/apache/flink/streaming/api/functions/sink/filesystem/StreamingFileSink.html) +for more configuration options and more documentation about the workings and +interactions of bucket assigners and rolling policies. + +#### Using Bulk-encoded Output Formats + +In the above example we used an `Encoder` that can encode or serialize each +record individually. The streaming file sink also supports bulk-encoded output +formats such as [Apache Parquet](http://parquet.apache.org). To use these, +instead of `StreamingFileSink.forRowFormat()` you would use +`StreamingFileSink.forBulkFormat()` and specify a `BulkWriter.Factory`. + +[ParquetAvroWriters]({{ site.baseurl }}/api/java/org/apache/flink/formats/parquet/avro/ParquetAvroWriters.html) +has static methods for creating a `BulkWriter.Factory` for various types. + +<div class="alert alert-info"> + <b>IMPORTANT:</b> Bulk-encoding formats can only be combined with the + `OnCheckpointRollingPolicy`, which rolls the in-progress part file on + every checkpoint. +</div> + +{% top %} ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
