selectQueryItr set fromNext for pagination, simplify pagination logic

src/main/scala/org/apache/spark/sql/sources/druid/DruidSelectResultIterator.scala

@@ -94,6 +94,12 @@ private class DruidSelectResultIterator(val useSmile : Boolean,
     val pagingIdentifiersJV: JsonAST.JValue = jValDeser.deserialize(jp, ctxt)
     nextPagingIdentifiers = pagingIdentifiersJV.extract[Map[String, Int]]
 
+//    nextPagingIdentifiers = nextPagingIdentifiers.map {
+//      case (s,i) if !selectSpec.descending => (s, i + 1)
+//      case (s,i) if selectSpec.descending => (s, i - 1)
+//    }
+
+
     // 1.2.2 events events field
     t = jp.nextToken // FIELD_NAME, jp.getCurrentName == events
     t = jp.nextToken // START_ARRAY
@@ -118,21 +124,8 @@ private class DruidSelectResultIterator(val useSmile : Boolean,
       val o: JsonAST.JValue = jValDeser.deserialize(jp, ctxt)
       val r = o.extract[SelectResultRow]
       t = jp.nextToken()
-      if (!thisRoundHadData) {
-        // if this the first row in this round,
-        // check that it's offset is greater
-        // than the nextPagingIdentifiers value
-        val nextOffset = nextPagingIdentifiers(r.segmentId)
-        if (r.offset >= nextOffset) {
-          finished = true
-          null
-        } else {
-          thisRoundHadData = true
-          r
-        }
-      } else {
-        r
-      }
+      thisRoundHadData = true
+      r
     }
   }
 

src/main/scala/org/sparklinedata/druid/DruidQuerySpec.scala

@@ -917,7 +917,8 @@ case class SearchQuerySpecWithSegIntervals(
 }
 
 case class PagingSpec(pagingIdentifiers : Map[String, Int],
-                      threshold : Int)
+                      threshold : Int,
+                      fromNext : Option[Boolean] = None)
 
 abstract class SelectSpec extends QuerySpec {
   self : Product =>
@@ -956,6 +957,8 @@ abstract class SelectSpec extends QuerySpec {
       case dc => dc.name
     }
 
+  def descending : Boolean
+
 }
 
 case class SelectSpecWithIntervals(queryType: String,
@@ -984,7 +987,7 @@ case class SelectSpecWithIntervals(queryType: String,
   )
 
   def withPagingIdentifier(ps :  Map[String, Int]) = {
-    copy(pagingSpec = pagingSpec.copy(pagingIdentifiers = ps))
+    copy(pagingSpec = pagingSpec.copy(pagingIdentifiers = ps, fromNext = Some(true)))
   }
 
   override def setIntervals(ins : List[Interval]) = this.copy(intervals = ins.map(_.toString))
@@ -1021,7 +1024,7 @@ case class SelectSpecWithSegmentIntervals(queryType: String,
   extends SelectSpec {
 
   def withPagingIdentifier(ps :  Map[String, Int]) = {
-    copy(pagingSpec = pagingSpec.copy(pagingIdentifiers = ps))
+    copy(pagingSpec = pagingSpec.copy(pagingIdentifiers = ps, fromNext = Some(true)))
   }
 
   override def setSegIntervals(segInAssignments: List[(DruidSegmentInfo, Interval)]): QuerySpec = {