## What changes were proposed in this pull request?
Logging in driver when loading single large unsplittable file via `sc.textFile` or csv/json datasouce.
Current condition triggering logging is
* only generate one partition
* file is unsplittable, possible reason is:
- compressed by unsplittable compression algo such as gzip.
- multiLine mode in csv/json datasource
- wholeText mode in text datasource
* file size exceed the config threshold `spark.io.warning.largeFileThreshold` (default value is 1GB)
## How was this patch tested?
Manually test.
Generate one gzip file exceeding 1GB,
```
base64 -b 50 /dev/urandom | head -c 2000000000 > file1.txt
cat file1.txt | gzip > file1.gz
```
then launch spark-shell,
run
```
sc.textFile("file:///path/to/file1.gz").count()
```
Will print log like:
```
WARN HadoopRDD: Loading one large unsplittable file file:/.../f1.gz with only one partition, because the file is compressed by unsplittable compression codec
```
run
```
sc.textFile("file:///path/to/file1.txt").count()
```
Will print log like:
```
WARN HadoopRDD: Loading one large file file:/.../f1.gz with only one partition, we can increase partition numbers by the `minPartitions` argument in method `sc.textFile
```
run
```
spark.read.csv("file:///path/to/file1.gz").count
```
Will print log like:
```
WARN CSVScan: Loading one large unsplittable file file:/.../f1.gz with only one partition, the reason is: the file is compressed by unsplittable compression codec
```
run
```
spark.read.option("multiLine", true).csv("file:///path/to/file1.gz").count
```
Will print log like:
```
WARN CSVScan: Loading one large unsplittable file file:/.../f1.gz with only one partition, the reason is: the csv datasource is set multiLine mode
```
JSON and Text datasource also tested with similar cases.
Please review https://spark.apache.org/contributing.html before opening a pull request.
Closes#25134 from WeichenXu123/log_gz.
Authored-by: WeichenXu <weichen.xu@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
26d03b62e2