Improve table data preallocation and potential slice leak. This chang…

…e changes the behavior to preallocate slices to the the predicted length and capacity. It also remove some slice usage that could lead to memory preasure since it does not release data for GC to pick up

bql/table/table.go

@@ -281,21 +281,26 @@ func (t *Table) DotProduct(t2 *Table) error {
 	}
 	// Update the data.
 	td := t.data
-	t.data = []Row{}
+	cnt, size := 0, len(td)*len(t2.data)
+	t.data = make([]Row, size, size) // Preallocate resulting table.
 	for _, r1 := range td {
 		for _, r2 := range t2.data {
-			t.data = append(t.data, MergeRows([]Row{r1, r2}))
+			t.data[cnt] = MergeRows([]Row{r1, r2})
+			cnt++
 		}
 	}
 	return nil
 }
 
 // DeleteRow removes the row at position i from the table.
 func (t *Table) DeleteRow(i int) error {
+	td := make([]Row, len(t.data)-1, len(t.data)-1) // Preallocate resulting table.
 	if i < 0 || i >= len(t.data) {
 		return fmt.Errorf("cannot delete row %d from a table with %d rows", i, len(t.data))
 	}
-	t.data = append(t.data[:i], t.data[i+1:]...)
+	copy(td, t.data[:i])
+	copy(td[i:], t.data[i+1:])
+	t.data = td
 	return nil
 }
 
@@ -307,7 +312,9 @@ func (t *Table) Truncate() {
 // Limit keeps the initial ith rows.
 func (t *Table) Limit(i int64) {
 	if int64(len(t.data)) > i {
-		t.data = t.data[:i]
+		td := make([]Row, i, i) // Preallocate resulting table.
+		copy(td, t.data[:i])
+		t.data = td
 	}
 }