fix bug in spill file name allocation (#1391)

The recent refactor of the spill code into its own module introduced
a bug where the file names could collide because they were named
after their position in the spill table, which grows and shrinks.
This caused distinct spills to have the same file name.  The fix is
to track the total number of spills and name the file after this.

proc/spill/merge.go

@@ -16,6 +16,7 @@ import (
 // disk a chunk at a time, then read back and merged in sorted order, effectively
 // implementing an external merge sort.
 type MergeSort struct {
+ nspill int
  runs []*peeker
  compareFn expr.CompareFn
  tempDir string
@@ -60,12 +61,12 @@ func (r *MergeSort) Cleanup() {
 // the chunks sequentially.
 func (r *MergeSort) Spill(recs []*zng.Record) error {
  expr.SortStable(recs, r.compareFn)
- index := len(r.runs)
- filename := filepath.Join(r.tempDir, strconv.Itoa(index))
- runFile, err := newPeeker(filename, index, recs, r.zctx)
+ filename := filepath.Join(r.tempDir, strconv.Itoa(r.nspill))
+ runFile, err := newPeeker(filename, r.nspill, recs, r.zctx)
  if err != nil {
  return err
  }
+ r.nspill++
  heap.Push(r, runFile)
  return nil
 }