db:spark:dataset:partition

partitionBy(scala.collection.SeqcolNames)]]

partitionBy(String… colNames)

Apply function

foreachPartition(func) - Runs func on each partition of this Dataset.
mapPartitions - Returns a new Dataset that contains the result of applying func to each partition. Experimental

Sort

sortWithinPartitions - Returns a new Dataset with each partition sorted by the given expressions. This is the same operation as “SORT BY” in SQL (Hive QL).

Coalesce

coalesce - reduce the number of partitions - if you go from 1000 partitions to 100 partitions, there will not be a shuffle, instead each of the 100 new partitions will claim 10 of the current partitions.

Example:

// coalesce the data to a single file.
data.coalesce(1).write

Repartition

Repartition creates partitions based on the user’s input by performing a full shuffle on the data (after read)

repartition(int numPartitions)
repartition by column (takes the number of partition from spark.sql.shuffle.partitions)
repartitionByRange - range partition

If the number of partitions is not specified, the number is taken from spark.sql.shuffle.partitions.Returns a new Dataset partitioned by the given partitioning expressions. Same as DISTRIBUTE BY in SQL. All rows with the same Distribute By columns will go to the same reducer. However, Distribute By does not guarantee clustering or sorting properties on the distributed keys.

Support

Number of dynamic partitions created is XXXX, which is more than 1000.

Number of dynamic partitions created is 2100, which is more than 1000. 
To solve this try to set hive.exec.max.dynamic.partitions to at least 2100.;

The below configuration must be set before starting the spark application

spark.hadoop.hive.exec.max.dynamic.partitions

A set with Spark SQL Server will not work. You need to set the configuration at the start of the server.from https://github.com/apache/spark/pull/18769

Documentation / Reference

https://datanoon.com/blog/spark_repartition_coalesce/