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https://issues.apache.org/jira/browse/BEAM-10945?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17479257#comment-17479257
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Etienne Chauchot commented on BEAM-10945:
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[~egalpin] allowing the user to specify the number of bundles would be a
implementation leak and a violation of Beam portability. What happens is that
it is the native technology (spark, flink, dataflow ...) that chooses the
parallelism based on the one configured for the cluster. For ex for a single
cluster with 4 cores, an OP would configure spark (for ex) parallelism to 4.
When the beam source is translated to a spark source this configured
parallelism is read through the spark API by Beam and the corresponding number
of splits (4) is created. Split is the name of bundles for the source. If no
SDF is used and no reparallelise transform either, this parallelism of 4 will
be the one used throught the whole pipeline for parallel operations such as
map.
> ElasticsearchIO performs 0 division on DirectRunner
> ---------------------------------------------------
>
> Key: BEAM-10945
> URL: https://issues.apache.org/jira/browse/BEAM-10945
> Project: Beam
> Issue Type: Bug
> Components: io-java-elasticsearch, runner-direct
> Affects Versions: 2.23.0
> Environment: Beam 2.23
> Java 1.8.0_265
> Ubuntu 16.04
> Elastic version of cluster 7.9.1, cross cluster setup
> Parallelism of direct runner 8
> Reporter: Milan Nikl
> Priority: P3
>
> h1. Environment configuration
> In my company we use [Elasticsearch cross
> cluster|https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-cross-cluster-search.html#ccs-supported-apis]
> setup for search. Cluster version is 7.9.1.
> I intended to use ElasticsearchIO for reading application logs and
> subsequently producing some aggregated data.
> h1. Problem description
> # In cross cluster ES setup, there is no {{/<index>/_stats}} API available,
> so it is not possible to compute
> [ElasticsearchIO#getEstimatedSizeBytes|https://github.com/apache/beam/blob/master/sdks/java/io/elasticsearch/src/main/java/org/apache/beam/sdk/io/elasticsearch/ElasticsearchIO.java#L692]
> properly.
> # {{statsJson}} returned by the cluster looks like this:
> {quote}Unknown macro: \{ "_shards" }
> ,
> "_all" :
> Unknown macro: \{ "primaries" }
> ,
> "total" : \{ }
> },
> "indices" : \{ }
> }
> {quote}
> # That means that {{totalCount}} value cannot be parsed from the json and is
> thus set to {{0}}.
> # Which means that {{estimatedByteSize}} value [is set to
> 1|https://github.com/apache/beam/blob/master/sdks/java/io/elasticsearch/src/main/java/org/apache/beam/sdk/io/elasticsearch/ElasticsearchIO.java#L707]
> (Which itself is a workaround for similar issue.)
> # {{ElasticsearchIO#getEstimatedSizeBytes}} is used in
> [BoundedReadEvaluatorFactory#getInitialInputs|https://github.com/apache/beam/blob/master/runners/direct-java/src/main/java/org/apache/beam/runners/direct/BoundedReadEvaluatorFactory.java#L212]
> which does not check the value and performs division of two {{long}} values,
> which of course results in {{0}} for any {{targetParallelism > 1}}.
> # Then
> [ElasticsearchIO#split|https://github.com/apache/beam/blob/master/sdks/java/io/elasticsearch/src/main/java/org/apache/beam/sdk/io/elasticsearch/ElasticsearchIO.java#L665]
> is called with {{indexSize = 1}} and {{desiredBundleSizeBytes = 1}}. Which
> sets {{nbBundlesFloat}} value to infinity.
> # Even though the number of bundles is ceiled at {{1024}}, reading from 1024
> BoundedElasticsearchSources concurrently makes the ElasticsearchIO virtually
> impossible to use on direct runner.
> h1. Resolution suggestion
> I still haven't tested reading from ElasticsearchIO on proper runner (we use
> flink 1.10.2), so I cannot either confirm or deny its functionality on our
> elastic setup. At the moment I'm just suggesting few checks of input values
> so the zero division and unnecessary parallelism problems are eliminated on
> direct runner.
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