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https://issues.apache.org/jira/browse/SPARK-15719?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16814061#comment-16814061
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Ruslan Dautkhanov commented on SPARK-15719:
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[~lian cheng] quick question on this part from the description -
{quote}
when schema merging is enabled, we need to read footers of all files anyway to
do the merge
{quote}
Is that still accurate in current Spark 2.3/ 2.4?
I was looking ParquetFileFormat.inferSchema and it does look at
`_common_metadata` and `_metadata` files here -
https://github.com/apache/spark/blob/v2.4.1/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala#L231
or Spark would still need to look at all files in all partitions, not actually
all parquet files?
Thank you.
> Disable writing Parquet summary files by default
> ------------------------------------------------
>
> Key: SPARK-15719
> URL: https://issues.apache.org/jira/browse/SPARK-15719
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0
> Reporter: Cheng Lian
> Assignee: Cheng Lian
> Priority: Major
> Labels: release_notes, releasenotes
> Fix For: 2.0.0
>
>
> Parquet summary files are not particular useful nowadays since
> # when schema merging is disabled, we assume schema of all Parquet part-files
> are identical, thus we can read the footer from any part-files.
> # when schema merging is enabled, we need to read footers of all files anyway
> to do the merge.
> On the other hand, writing summary files can be expensive because footers of
> all part-files must be read and merged. This is particularly costly when
> appending small dataset to large existing Parquet dataset.
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