// Save metric and index into db.
func (d *Detector) save(m *models.Metric, idx *models.Index) error {
// Save index.
if err := d.db.Index.Put(idx); err != nil {
return err
}
// Save metric.
m.LinkTo(idx) // Important
if err := d.db.Metric.Put(m); err != nil {
return err
}
return nil
}
// analyze given metric with 3sigma, returns the new index.
// Steps:
// 1. Get index.
// 2. Get history values.
// 3. Do 3sigma calculation.
// 4. Move the index next.
func (d *Detector) analyze(idx *models.Index, m *models.Metric, rules []*models.Rule) *models.Index {
fz := idx != nil && d.shouldFill0(m, rules)
if idx != nil {
m.LinkTo(idx)
}
vals, err := d.values(m, fz)
if err != nil {
return nil
}
d.div3Sigma(m, vals)
return d.nextIdx(idx, m, d.pickTrendingFactor(rules))
}
// div3Sigma sets given metric score and average via 3-sigma.
// states that nearly all values (99.7%) lie within the 3 standard deviations
// of the mean in a normal distribution.
func (d *Detector) div3Sigma(m *models.Metric, vals []float64) {
if len(vals) == 0 {
m.Score = 0
m.Average = m.Value
return
}
// Values average and standard deviation.
avg := mathutil.Average(vals)
std := mathutil.StdDev(vals, avg)
// Set metric average
m.Average = avg
// Set metric score
if len(vals) <= int(d.cfg.Detector.LeastCount) { // Number of values not enough
m.Score = 0
return
}
last := m.Value
if std == 0 { // Eadger
switch {
case last == avg:
m.Score = 0
case last > avg:
m.Score = 1
case last < avg:
m.Score = -1
}
return
}
m.Score = (last - avg) / (3 * std) // 3-sigma
}
// Test metric and index with rules.
// The following function will fill the m.TestedRules.
func (d *Detector) test(m *models.Metric, idx *models.Index, rules []*models.Rule) {
for _, rule := range rules {
if rule.Test(m, idx, d.cfg) {
// Add tested ok rules.
m.TestedRules = append(m.TestedRules, rule)
}
}
}
// decodeKey decodes db key into metric, this will fill metric name and metric
// stamp.
func decodeKey(key []byte, m *models.Metric) error {
s := string(key)
if len(s) <= stampLen {
return ErrCorrupted
}
// First substring is Name.
idx := len(s) - stampLen
m.Name = s[:idx]
// Last substring is Stamp.
str := s[idx:]
n, err := strconv.ParseUint(str, convBase, 32)
if err != nil {
return err
}
m.Stamp = horizon + uint32(n)
return nil
}