Remove duplicate slice during Silences query

[ultrotter]

If there are a lot of silences Silences.query, for queries without
q.ids, first copies all their pointers to a slice, causing a lot of
allocations, and then does it again to a new shorter slice filtered by
the query. We avoid this by only adding to the result slice in case of a
match. This creates savings for each queries, scaling with the number of silences.

[siavashs]

What do you think about the following?

• define a new type for []*pb.Silence
• add this method to that type
• pass s as an argument to that method

for example:

Suggested change

	func (s *Silences) appendIfFiltersMatch(res *[]*pb.Silence, sil *pb.Silence, q *query, now time.Time) error {
	type result []*pb.Silence
	func (r *result) appendOnMatch(s *Silences, sil *pb.Silence, q *query, now time.Time) error {

[Spaceman1701]

If the concern is the mutation of the res argument, I think we could just write

Suggested change

	func (s *Silences) appendIfFiltersMatch(res *[]*pb.Silence, sil *pb.Silence, q *query, now time.Time) error {
	func (s *Silences) appendIfFiltersMatch(res []*pb.Silence, sil *pb.Silence, q *query, now time.Time) ([]*pb.Silence, error) {
	for _, f := range q.filters {
	ok, err := f(sil, s, now)
	if err != nil {
	return res, err
	}
	if !ok {
	return res, nil
	}
	}
	return append(res, cloneSilence(sil)), nil
	}

[Spaceman1701]

And this would be called like

var err error
res, err = appendIfFiltersMatch(res, sil, now)
if err != nil {
  // whatever
}

[ultrotter]

I tried going for @Spaceman1701's approach to avoid defining a new internal type with a one method just for this... Hopefully it's as clear!

[siavashs]

LGTM, do you mind also adding inline docs to the logic so it is clear for people looking at the code later on?

[rajagopalanand]

LGTM