Pawel Szczur created BEAM-365: --------------------------------- Summary: TextIO withoutSharding causes Flink to throw IllegalStateException Key: BEAM-365 URL: https://issues.apache.org/jira/browse/BEAM-365 Project: Beam Issue Type: Bug Components: runner-flink Affects Versions: 0.2.0-incubating Reporter: Pawel Szczur
The exception: {code}java.lang.IllegalStateException: Shard name template '' only generated 1 distinct file names for 3 files{code} The initial discussion took place some time ago, the {{withoutSharding}} was then silently ignored. Explanation from Aljoscha Krettek: {quote} Hi, the issue is a bit more complicated and involves the Beam sink API and the Flink runner. I'll have to get a bit into how Beam sinks work. The base class for sinks is Sink (TextIO.write gets translated to Write.to(new TextSink())). Write.to normally gets translated to three ParDo operations that cooperate to do the writing: - "Initialize": this does initial initialization of the Sink, this is run only once, per sink, non-parallel. - "WriteBundles": this gets an initialized sink on a side-input and the values to write on the main input. This runs in parallel, so for Flink, if you set parallelism=6 you'll get 6 parallel instances of this operation at runtime. This operation forwards information about where it writes to downstream. This does not write to the final file location but an intermediate staging location. - "Finalize": This gets the initialized sink on the main-input and and the information about written files from "WriteBundles" as a side-input. This also only runs once, non-parallel. Here we're writing the intermediate files to a final location based on the sharding template. The problem is that Write.to() and TextSink, as well as all other sinks, are not aware of the number of shards. If you set "withoutSharding()" this will set the shard template to "" (empty string) and the number of shards to 1. "WriteBundles", however is not aware of this and will write 6 intermediate files if you set parallelism=6. In "Finalize" we will copy an intermediate file to the same final location 6 times based on the sharding template. The end result is that you only get one of the six result shards. The reason why this does only occur in the Flink runner is that all other runners have special overrides for TextIO.Write and AvroIO.Write that kick in if sharding control is required. So, for the time being this is a Flink runner bug and we might have to introduce special overrides as well until this is solved in the general case. Cheers, Aljoscha {quote} Original discussion: http://mail-archives.apache.org/mod_mbox/incubator-beam-user/201606.mbox/%3CCAMdX74-VPUsNOc9NKue2A2tYXZisnHNZ7UkPWk82_TFexpnySg%40mail.gmail.com%3E -- This message was sent by Atlassian JIRA (v6.3.4#6332)