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https://issues.apache.org/jira/browse/SPARK-32582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17175981#comment-17175981
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Lantao Jin edited comment on SPARK-32582 at 8/12/20, 4:31 AM:
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{quote}
I remember I investigated this issue and Hadoop API itself lists in batch.
There streaming way of listing isn't possible.
{quote}
Yes, we could list status in one partition if it is a partitioned table. For a
non-partitioned table, it still lists all files. We assume too many files in a
non-partitioned table is a bad design in data warehouse.
{quote}
We can add one more mode "INFER_WITH_SAMPLE".
{quote}
I am not sure it would be helpful since there is no API in Hadoop to list
partial files in a folder.
But if you mean listing all files then pick some of them, yes it might be
helpful for merging schema. But I thought the performance bottleneck is listing
files in a mass partition table.
was (Author: cltlfcjin):
{quote}
I remember I investigated this issue and Hadoop API itself lists in batch.
There streaming way of listing isn't possible.
{quote}
Yes, we could list status in one partition if it is a partitioned table. For a
non-partitioned table, it still lists all files. We assume too many files in a
non-partitioned table is a bad design in data warehouse.
{quote}
We can add one more mode "INFER_WITH_SAMPLE".
{quote}
I am not sure it would be helpful since there is no API in Hadoop to list
partial files in a folder.
> Spark SQL Infer Schema Performance
> ----------------------------------
>
> Key: SPARK-32582
> URL: https://issues.apache.org/jira/browse/SPARK-32582
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.4.6, 3.0.0
> Reporter: Jarred Li
> Priority: Major
>
> When infer schema is enabled, it tries to list all the files in the table,
> however only one of the file is used to read schema informaiton. The
> performance is impacted due to list all the files in the table when the
> number of partitions is larger.
>
> See the code in
> "[https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/orc/OrcUtils.scala#L88|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/orc/OrcUtils.scala#88]";,
> all the files in the table are input, however only one of the file's schema
> is used to infer schema.
>
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