Reduce memory allocation in bulk op

[feliixx]

Use memory pooling to reuse bulkActions and avoid some allocations

Here are some benchmarks results:

benchmark                 old ns/op     new ns/op     delta
BenchmarkBulkInsert-2     4441204       4473256       +0.72%

benchmark                 old allocs     new allocs     delta
BenchmarkBulkInsert-2     1967           1945           -1.12%

benchmark                 old bytes     new bytes     delta
BenchmarkBulkInsert-2     89338         37986         -57.48%

and here is the benchmark code:

func BenchmarkBulkInsert(b *testing.B) {
	var documents [1000]bson.Raw
	for i := range documents {
		data, _ := bson.Marshal(bson.M{"n": i})
		documents[i] = bson.Raw{Kind: bson.ElementDocument, Data: data}
	}
	s, err := mgo.Dial("mongodb://localhost:27017")
	if err != nil {
		b.Fail()
	}
	c := s.DB("bench").C("test")
	b.ResetTimer()

	for n := 0; n < b.N; n++ {
		bulk := c.Bulk()
		bulk.Unordered()
		for _, doc := range documents {
			bulk.Insert(doc)
		}
		_, err := bulk.Run()
		if err != nil {
			b.Fail()
		}
	}
}

[domodwyer]

This needs to be above the if !ok check - if an operation fails the actions leak.

[domodwyer]

Hey @feliixx,

Good idea and an easy win! Just need to return the action back to the pool before the check but quite happy to merge after.

Dom

memory leak

[feliixx]

Hi @domodwyer

thanks or the review, it should be fine now

[domodwyer]

Fantastic, cheers @feliixx!