SPARKC-312: Implementing FilterOptimizer #1019
Conversation
…e.optimization + some more tests
| val withPushdown = Map("pushdown" -> "true") | ||
| val withWhereClauseOptimizationEnabled = Map("spark.cassandra.sql.enable.where.clause.optimization" -> "true") |
There was a problem hiding this comment.
Replace the string here with the parameter defined in the conf file
EnableWhereClauseOptimizationParam.name just in case we change things later :)
| @@ -79,7 +78,15 @@ private[cassandra] class CassandraSourceRelation( | |||
| def buildScan(): RDD[Row] = baseRdd.asInstanceOf[RDD[Row]] | |||
|
|
|||
| override def unhandledFilters(filters: Array[Filter]): Array[Filter] = filterPushdown match { | |||
| case true => predicatePushDown(filters).handledBySpark.toArray | |||
| case true => | |||
| val optimizedFilters = FiltersOptimizer(filters).build() | |||
There was a problem hiding this comment.
I think it may be better if we got the FilterOptimzer into the predicatePushDown function, then I think we could skip having it written in a bunch of places.
| * val Array(f1, f2, ... fn) = ... // such that `where f1 AND f2 AND ... AND fn` | ||
| * | ||
| */ | ||
| class FiltersOptimizer(filters: Array[Filter]) { |
There was a problem hiding this comment.
I'm a little confused why there is a separate class here, do we ever use this without calling .build() immediately after?
| val filteredRdd = maybePushdownFilters(prunedRdd, pushdownFilters) | ||
| val optimizedFilters = new FiltersOptimizer(filters).build() | ||
| val optimizationCanBeApplied = isOptimizationAvailable(optimizedFilters) | ||
| val filteredRdd = if(optimizationCanBeApplied) { |
There was a problem hiding this comment.
I think this is a rather dangerous optimization sometimes, so I think we should default to off. For example
Table where x < 3 or x > 5 and x ranges from 1 to 10000. Doing two scans here is probably much more expensive than a single scan.
There was a problem hiding this comment.
I thought that both scans will be done in parallel. By default this option is set to false.
FilterOptimizer will to transform
whereclause to equivalent disjunction normal form.For example where clause
a = 5 and (b > 5 or b < 3)can be transformed to equivalenta = 5 and b > 5 or a =5 and b < 3, so now we can create two different table scans with where clausea = 5 and b > 5anda =5 andb < 3and union them.