[query] Improve readerIterator performance (m3db#3512)

src/dbnode/encoding/m3tsz/iterator.go

@@ -56,6 +56,7 @@ type readerIterator struct {
  mult uint8 // current int multiplier
  sig uint8 // current number of significant bits for int diff
 
+ curr ts.Datapoint
  intOptimized bool // whether encoding scheme is optimized for ints
  isFloat bool // whether encoding is in int or float
 
@@ -94,6 +95,14 @@ func (it *readerIterator) Next() bool {
  it.readFirstValue()
  }
 
+ it.curr.Timestamp = it.tsIterator.PrevTime.ToTime()
+ it.curr.TimestampNanos = it.tsIterator.PrevTime
+ if !it.intOptimized || it.isFloat {
+ it.curr.Value = math.Float64frombits(it.floatIter.PrevFloatBits)
+ } else {
+ it.curr.Value = convertFromIntFloat(it.intVal, it.mult)
+ }
+
  return it.hasNext()
 }
 
@@ -219,18 +228,7 @@ func (it *readerIterator) readBits(numBits uint8) (res uint64) {
 // Users should not hold on to the returned Annotation object as it may get invalidated when
 // the iterator calls Next().
 func (it *readerIterator) Current() (ts.Datapoint, xtime.Unit, ts.Annotation) {
- dp := ts.Datapoint{
- Timestamp: it.tsIterator.PrevTime.ToTime(),
- TimestampNanos: it.tsIterator.PrevTime,
- }
-
- if !it.intOptimized || it.isFloat {
- dp.Value = math.Float64frombits(it.floatIter.PrevFloatBits)
- } else {
- dp.Value = convertFromIntFloat(it.intVal, it.mult)
- }
-
- return dp, it.tsIterator.TimeUnit, it.tsIterator.PrevAnt
+ return it.curr, it.tsIterator.TimeUnit, it.tsIterator.PrevAnt
 }
 
 // Err returns the error encountered