nehsyc commented on a change in pull request #14530:
URL: https://github.com/apache/beam/pull/14530#discussion_r616967664
##########
File path: sdks/java/core/src/main/java/org/apache/beam/sdk/io/WriteFiles.java
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@@ -744,7 +735,84 @@ public void processElement(@Element UserT element,
ProcessContext context)
KV.of(hashDestination(destination,
destinationCoder), element));
}
}))
- .setCoder(KvCoder.of(VarIntCoder.of(), input.getCoder()))
+ .setCoder(KvCoder.of(VarIntCoder.of(), input.getCoder()));
+
+ if (input.getWindowingStrategy().needsMerge()) {
+ // To make sure that the elements are partitioned by original input
windows and to work with
+ // merging windows such as sessions, we firstly group the elements by
destination to reify
+ // the window, if the window needs to be merged, and then perform
sharded writes for each
+ // destination and window pair.
+ Coder<BoundedWindow> windowCoder =
+ (Coder<BoundedWindow>)
input.getWindowingStrategy().getWindowFn().windowCoder();
+ return reifyWindowAndWrite(keyedInput, windowCoder, input.getCoder());
+ } else {
+ return write(keyedInput, input.getCoder());
+ }
+ }
+
+ private PCollection<List<FileResult<DestinationT>>> reifyWindowAndWrite(
+ PCollection<KV<Integer, UserT>> keyedInput,
+ Coder<BoundedWindow> windowCoder,
+ Coder<UserT> inputCoder) {
+ PCollection<KV<ValueInSingleWindow<Integer>, UserT>> windowedInput =
+ keyedInput
+ .apply("GroupByDestination", GroupByKey.create())
Review comment:
This GBK could be a bottleneck although we "reshard" before the write
which is potentially more expensive. I don't have a better idea other than
reifying the window in the keys.
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