cybertec-postgresql / pgwatch / 34598180616

88%

push

github

[*] cut allocations in `PrometheusWriter.WritePromMetrics` (#1550)

Everything that does not depend on the row is now computed once per
envelope instead of once per row x field:

- fqName and the gauge/counter decision are memoized per field, and the
  namespace prefix is concatenated once instead of via fmt.Sprintf;
- prometheus.Desc is cached per (fqName, label keys). NewDesc allocates
  ~6+2N objects and runs regexp validation and two sorts on every call;
- numeric columns are converted with a direct float64(t) conversion
  instead of strconv.ParseFloat(fmt.Sprintf("%v", v)); only float32
  values may differ at the ULP level;
- the dead labels map allocation and the map[bool]float64 literal are
gone.

BenchmarkWritePromMetrics (500 rows, 3 tags, 8 columns):
  before  10.5 ms/op   5.14 MB/op   141k allocs/op
  after    6.3 ms/op   3.70 MB/op    86k allocs/op

61 of 69 new or added lines in 1 file covered. (88.41%)

5443 of 6192 relevant lines covered (87.9%)

1.0 hits per line