Jan Kuipers created BEAM-6064:
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Summary: Python BigQuery performance much worse than Java
Key: BEAM-6064
URL: https://issues.apache.org/jira/browse/BEAM-6064
Project: Beam
Issue Type: Bug
Components: sdk-py-core
Affects Versions: 2.8.0
Reporter: Jan Kuipers
Assignee: Ahmet Altay
The performance of reading from BigQuery in Python seems to be much worse than
the performance of it in Java.
To reproduce this, I've run the following two programs on the Google Cloud,
which basically read the weights from the public data set "natality" and
outputs the top 100 largest weights.
Python:
{code:java}
# <cut imports>
options = PipelineOptions()
options.view_as(StandardOptions).runner = 'DataflowRunner'
# <cut more options>
pipeline = Pipeline(options=options)
(pipeline
| 'Read' >> beam.io.Read(beam.io.BigQuerySource(query='SELECT weight_pounds
FROM [bigquery-public-data:samples.natality]'))
| 'MapToFloat' >> beam.Map(lambda elem: elem['weight_pounds'])
| 'Top' >> beam.combiners.Top.Largest(100)
| 'MapToString' >> beam.Map(lambda elem: str(elem))
| 'Write' >> beam.io.WriteToText("<output-file>"))
pipeline.run()
{code}
Java:
{code:java}
// <cut imports>
public class Natality {
public static void main(String[] args) {
DataflowPipelineOptions options =
PipelineOptionsFactory.create().as(DataflowPipelineOptions.class);
options.setRunner(DataflowRunner.class);
// <cut more options>
Pipeline pipeline = Pipeline.create(options);
pipeline.apply("Read", BigQueryIO.readTableRows()
.fromQuery("SELECT weight_pounds FROM
[bigquery-public-data:samples.natality]"))
.apply("MapToDouble", MapElements
.into(TypeDescriptors.doubles())
.via(row -> {
Object obj = row.get("weight_pounds");
return (obj == null ? 0.0 : (Double) obj);
}))
.apply("Top", Top.largest(100))
.apply("MapToString", MapElements
.into(TypeDescriptors.strings())
.via(weight -> weight.toString()))
.apply("Write", TextIO.write().to("<output-file>"));
pipeline.run().waitUntilFinish();
}
}
{code}
The "<cut more options>" are basic options like project, job name, temp
location, etc. Both programs produce identical outputs.
Running these programs launches a DataFlow job on the Google Cloud with the
following results (data from the Google Cloud Platform web interface; I could
add screenshots if that were allowed).
Python:
{noformat}
Read Succeeded 1 hr 40 min 40 sec
MapToFloat Succeeded 2 min 43 sec
Top Succeeded 5 min 25 sec
MapToString Succeeded 0 sec
Write Succeeded 3 sec{noformat}
Java:
{noformat}
Read Succeeded 4 min 45 sec
MapToDouble Succeeded 45 sec
Top Succeeded 52 sec
MapToString Succeeded 0 sec
Write Succeeded 1 sec
{noformat}
As you can see, there is an enormous performance hit in Python w.r.t. the
reading from BigQuery: 1h40m vs less than 5 minutes.
Furthermore the other standard operations (like Top) are also much slower in
Python than in Java.
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