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https://issues.apache.org/jira/browse/BEAM-5427?focusedWorklogId=146519&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-146519
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ASF GitHub Bot logged work on BEAM-5427:
----------------------------------------
Author: ASF GitHub Bot
Created on: 21/Sep/18 18:11
Start Date: 21/Sep/18 18:11
Worklog Time Spent: 10m
Work Description: youngoli commented on a change in pull request #6439:
[BEAM-5427] Fix and update sample code for CombineFn.
URL: https://github.com/apache/beam/pull/6439#discussion_r219583784
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java
##########
@@ -289,6 +305,21 @@ private Combine() {
* arbitrary tree structure. Commutativity is required because any order of
the input values is
* ignored when breaking up input values into groups.
*
+ * <h3>Note on Data Encoding</h3>
+ *
+ * <p>Data encoding is required to make CombineFn work. The sample code
above implements {@code
+ * java.io.Serializable} so that CombineFn in consequence makes use of
SerializableCoder to encode
+ * the data. In many cases though, relying on Serializable could be less
preferred for efficiency
+ * considerations. In addition, Serializable may not be applicable in all
situations. There are
+ * two alternatives to make data encoding work for AverageFn:
+ *
+ * <ul>
+ * <li>Generic Coder class. Implement an encoder class explicitly and use
{@code @DefaultCoder}
+ * tag.
+ * <li>{@link CombineFn} Specific way. While extending {@link CombineFn},
overwrite both {@link
+ * #getAccumulatorCoder} and {@link #getDefaultOutputCoder}.
+ * </ul>
+ *
Review comment:
I think I get what you're trying to explain in this note, but the grammer is
a little bit awkward. I'd like to suggest this to make it sound more natural:
```
* <h3>Note on Data Encoding</h3>
*
* <p>Some form of data encoding is required when using custom types in a
CombineFn which do not
* have well-known coders. The sample code above uses a custom Accumulator
which it encodes by
* making it {@code java.io.Serializable}. However in cases where {@code
java.io.Serializable} is
* not efficient or applicable, there are two alternatives for encoding:
*
* <ul>
* <li>Generic coder class: Implement a coder class explicitly and use
the {@code @DefaultCoder}
* tag.
* <li>CombineFn specific way: While extending CombineFn, overwrite both
{@link
* #getAccumulatorCoder} and {@link #getDefaultOutputCoder}.
* </ul>
```
If any parts of that sound incorrect feel free to fix.
Also, although I can review the writing in this documentation change, I
can't really review the correctness of it since I'm not very familiar with
coders. I would recommend adding a reviewer who is familiar with coders and can
vet that this is correct. Maybe lukecwik since he's also a committer and can
also take care of merging.
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Issue Time Tracking
-------------------
Worklog Id: (was: 146519)
Time Spent: 1h 20m (was: 1h 10m)
> Fix sample code (AverageFn) in Combine.java
> -------------------------------------------
>
> Key: BEAM-5427
> URL: https://issues.apache.org/jira/browse/BEAM-5427
> Project: Beam
> Issue Type: Improvement
> Components: examples-java
> Reporter: Ruoyun Huang
> Assignee: Ruoyun Huang
> Priority: Minor
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> Sample code missing coder.
> In its current state, job run fails with Coder missing error.
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