feat(sparkJobs): If tracing downsampler, log chunks read from cassand…

…ra (#756)

spark-jobs/src/main/scala/filodb/downsampler/chunk/BatchDownsampler.scala

@@ -270,6 +270,16 @@ class BatchDownsampler(settings: DownsamplerSettings) extends Instance with Seri
         val tsAcc = chunkset.vectorAccessor(timestampCol)
         val tsReader = rawPartToDownsample.chunkReader(timestampCol, tsAcc, tsPtr).asLongReader
 
+        if (shouldTrace) {
+          downsamplers.zipWithIndex.foreach { case (d, i) =>
+            val ptr = chunkset.vectorAddress(i)
+            val acc = chunkset.vectorAccessor(i)
+            val reader = rawPartToDownsample.chunkReader(i, acc, ptr)
+            DownsamplerContext.dsLogger.info(s"Hex Vectors: Col $i for ${rawPartToDownsample.stringPartition} uses " +
+              s"downsampler ${d.encoded} vector=${reader.toHexString(acc, ptr)}RemoveEOL")
+          }
+        }
+
         val startRow = tsReader.binarySearch(tsAcc, tsPtr, userTimeStart) & 0x7fffffff
         // userTimeEndExclusive-1 since ceilingIndex does an inclusive check
         val endRow = Math.min(tsReader.ceilingIndex(tsAcc, tsPtr, userTimeEndExclusive - 1), chunkset.numRows - 1)