What is the meaning of Project node in Sparks execution plan?
I have a plan containing the following:
+- Project [dm_country#population#6a1ad864-235f-4761-9a6d-0ca2a2b40686#834, dm_country#population#country#839, population#17 AS dm_country#population#population#844]
+- Project [dm_country#population#6a1ad864-235f-4761-9a6d-0ca2a2b40686#834, country#12 AS dm_country#population#country#839, population#17]
+- Project [6a1ad864-235f-4761-9a6d-0ca2a2b40686#22 AS dm_country#population#6a1ad864-235f-4761-9a6d-0ca2a2b40686#834, country#12, population#17]
+- RepartitionByExpression [country#12], 1000
+- Union
:- Project [ind#7 AS 6a1ad864-235f-4761-9a6d-0ca2a2b40686#22, country#12, population#17]
: +- Project [ind#7, country#12, population#2 AS population#17]
: +- Project [ind#7, country#1 AS country#12, population#2]
: +- Project [ind#0 AS ind#7, country#1, population#2]
: +- Relation[ind#0,country#1,population#2] JDBCRelation(schema_dbadmin.t_350) [numPartitions=100]
+- LogicalRDD [ind#45, country#46, population#47]