What does this property spark.sql.files.openCostInBytes do ?
This is official document definition:
The estimated cost to open a file, measured by the number of bytes could be scanned in the same time. This is used when putting multiple files into a partition. It is better to over-estimated, then the partitions with small files will be faster than partitions with bigger files (which is scheduled first). This configuration is effective only when using file-based sources such as Parquet, JSON and ORC.
But still didn't get it. Can anyone explain with small example that why and where its useful?