Configuring Automatic Merging of Small Files

Scenario

After the automatic small file merging feature is enabled, Spark writes data to the temporary directory and then checks whether the average file size of each partition is less than 16 MB (default value). If the average file size is less than 16 MB, the partition contains small files. Spark starts a job to merge these small files and writes the large files to the final table directory.

Constraints

Only Hive and DataSource tables can be written.
Parquet and ORC data formats are supported.

Parameter Configuration

Modify the following parameters in the Client installation directory/Spark/spark/conf/spark-defaults.conf file on the Spark client.

Parameter	Description	Default Value
spark.sql.mergeSmallFiles.enabled	If this parameter is set to true, Spark checks whether small files are written when writing data to the target table. If small files are found, Spark starts the file merging job.	false
spark.sql.mergeSmallFiles.threshold.avgSize	If the average file size of a partition is smaller than the value of this parameter, small file merging is started.	16 MB
spark.sql.mergeSmallFiles.maxSizePerTask	Target size of each file after the merging.	256 MB
spark.sql.mergeSmallFiles.moveParallelism	Maximum degree of parallelism of moving temporary files to the final directory. If the number of temporary files exceed the specified value, a file merging job is triggered.	10,000