Github user srowen commented on a diff in the pull request: https://github.com/apache/spark/pull/16157#discussion_r91445291 --- Diff: docs/programming-guide.md --- @@ -347,7 +347,7 @@ Some notes on reading files with Spark: Apart from text files, Spark's Scala API also supports several other data formats: -* `SparkContext.wholeTextFiles` lets you read a directory containing multiple small text files, and returns each of them as (filename, content) pairs. This is in contrast with `textFile`, which would return one record per line in each file. +* `SparkContext.wholeTextFiles` lets you read a directory containing multiple small text files, and returns each of them as (filename, content) pairs. This is in contrast with `textFile`, which would return one record per line in each file. It takes an optional second argument for controlling the minimal number of partitions (by default this is 2). It uses [CombineFileInputFormat](https://hadoop.apache.org/docs/current/api/org/apache/hadoop/mapreduce/lib/input/CombineFileInputFormat.html) internally in order to process large numbers of small files effectively by grouping files on the same executor into a single partition. This can lead to sub-optimal partitioning when the file sets would benefit from residing in multiple partitions (e.g., larger partitions would not fit in memory, files are replicated but a large subset is locally reachable from a single executor, subsequent transformations would benefit from multi-core processing). In those cases, set the `minPartitions` argume nt to enforce splitting. --- End diff -- Every element of the result is a file; it's fundamentally different from `textFile`, and can't be that each file therefore ends up in a partition. I don't think this merges files, right?
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