Use temp slice to append only once

Instead of checking `s.slice` on each call to append and regrow if
necessary, create a temporary slice with the maximum possible
capacity, and append that slice to `s.slice` outside the for loop,
effectively checking and regrowing `s.slice` only once.

This further improves CPU and memory consumption.

Author: inkel

pkg/phlaredb/symdb/dedup_slice.go

@@ -279,6 +279,7 @@ func (s *deduplicatingSlice[M, K, H]) ingest(elems []M, rewriter *rewriter) {
 	if len(missing) > 0 {
 		s.lock.Lock()
 		posSlice := int64(len(s.slice))
+		misSlice := make([]M, 0, len(missing))
 		for _, pos := range missing {
 			// check again if element exists
 			k := s.helper.key(elems[pos])
@@ -288,12 +289,13 @@ func (s *deduplicatingSlice[M, K, H]) ingest(elems []M, rewriter *rewriter) {
 			}
 
 			// add element to slice/map
-			s.slice = append(s.slice, s.helper.clone(elems[pos]))
+			misSlice = append(misSlice, s.helper.clone(elems[pos]))
 			s.lookup[k] = posSlice
 			rewritingMap[int64(s.helper.setID(uint64(pos), uint64(posSlice), &elems[pos]))] = posSlice
 			posSlice++
 			s.size.Add(s.helper.size(elems[pos]))
 		}
+		s.slice = append(s.slice, misSlice...)
 		s.lock.Unlock()
 	}