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Fix wording from "jitterSeed" -> "offsetSeed" for server-wide scrape offsets

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In digital communication, "jitter" usually refers to how much a signal deviates
from true periodicity, see https://en.wikipedia.org/wiki/Jitter. The way we are
using the "jitterSeed" in Prometheus does not affect the true periodicity at
all, but just introduces a constant phase shift (or offset) within the period.
So it would be more correct and less confusing to call the "jitterSeed" an
"offsetSeed" instead.

Signed-off-by: Julius Volz <julius.volz@gmail.com>
pull/12399/head
Julius Volz 3 years ago
parent 89af351730
commit cb045c0e4b
4 changed files with 24 additions and 24 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 12
      scrape/manager.go
  2. 18
      scrape/manager_test.go
  3. 14
      scrape/scrape.go
  4. 4
      scrape/target_test.go

12
scrape/manager.go
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@ -150,7 +150,7 @@ type Manager struct {
append storage.Appendable
graceShut chan struct{}
jitterSeed uint64 // Global jitterSeed seed is used to spread scrape workload across HA setup.
offsetSeed uint64 // Global offsetSeed seed is used to spread scrape workload across HA setup.
mtxScrape sync.Mutex // Guards the fields below.
scrapeConfigs map[string]*config.ScrapeConfig
scrapePools map[string]*scrapePool
@ -214,7 +214,7 @@ func (m *Manager) reload() {
level.Error(m.logger).Log("msg", "error reloading target set", "err", "invalid config id:"+setName)
continue
}
sp, err := newScrapePool(scrapeConfig, m.append, m.jitterSeed, log.With(m.logger, "scrape_pool", setName), m.opts)
sp, err := newScrapePool(scrapeConfig, m.append, m.offsetSeed, log.With(m.logger, "scrape_pool", setName), m.opts)
if err != nil {
level.Error(m.logger).Log("msg", "error creating new scrape pool", "err", err, "scrape_pool", setName)
continue
@ -234,8 +234,8 @@ func (m *Manager) reload() {
wg.Wait()
}
// setJitterSeed calculates a global jitterSeed per server relying on extra label set.
func (m *Manager) setJitterSeed(labels labels.Labels) error {
// setOffsetSeed calculates a global offsetSeed per server relying on extra label set.
func (m *Manager) setOffsetSeed(labels labels.Labels) error {
h := fnv.New64a()
hostname, err := osutil.GetFQDN()
if err != nil {
@ -244,7 +244,7 @@ func (m *Manager) setJitterSeed(labels labels.Labels) error {
if _, err := fmt.Fprintf(h, "%s%s", hostname, labels.String()); err != nil {
return err
}
m.jitterSeed = h.Sum64()
m.offsetSeed = h.Sum64()
return nil
}
@ -281,7 +281,7 @@ func (m *Manager) ApplyConfig(cfg *config.Config) error {
}
m.scrapeConfigs = c
if err := m.setJitterSeed(cfg.GlobalConfig.ExternalLabels); err != nil {
if err := m.setOffsetSeed(cfg.GlobalConfig.ExternalLabels); err != nil {
return err
}

18
scrape/manager_test.go
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@ -596,7 +596,7 @@ func TestManagerTargetsUpdates(t *testing.T) {
}
}
func TestSetJitter(t *testing.T) {
func TestSetOffsetSeed(t *testing.T) {
getConfig := func(prometheus string) *config.Config {
cfgText := `
global:
@ -617,24 +617,24 @@ global:
// Load the first config.
cfg1 := getConfig("ha1")
if err := scrapeManager.setJitterSeed(cfg1.GlobalConfig.ExternalLabels); err != nil {
if err := scrapeManager.setOffsetSeed(cfg1.GlobalConfig.ExternalLabels); err != nil {
t.Error(err)
}
jitter1 := scrapeManager.jitterSeed
offsetSeed1 := scrapeManager.offsetSeed
if jitter1 == 0 {
t.Error("Jitter has to be a hash of uint64")
if offsetSeed1 == 0 {
t.Error("Offset seed has to be a hash of uint64")
}
// Load the first config.
cfg2 := getConfig("ha2")
if err := scrapeManager.setJitterSeed(cfg2.GlobalConfig.ExternalLabels); err != nil {
if err := scrapeManager.setOffsetSeed(cfg2.GlobalConfig.ExternalLabels); err != nil {
t.Error(err)
}
jitter2 := scrapeManager.jitterSeed
offsetSeed2 := scrapeManager.offsetSeed
if jitter1 == jitter2 {
t.Error("Jitter should not be the same on different set of external labels")
if offsetSeed1 == offsetSeed2 {
t.Error("Offset seed should not be the same on different set of external labels")
}
}

14
scrape/scrape.go
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@ -279,7 +279,7 @@ const maxAheadTime = 10 * time.Minute
// returning an empty label set is interpreted as "drop"
type labelsMutator func(labels.Labels) labels.Labels
func newScrapePool(cfg *config.ScrapeConfig, app storage.Appendable, jitterSeed uint64, logger log.Logger, options *Options) (*scrapePool, error) {
func newScrapePool(cfg *config.ScrapeConfig, app storage.Appendable, offsetSeed uint64, logger log.Logger, options *Options) (*scrapePool, error) {
targetScrapePools.Inc()
if logger == nil {
logger = log.NewNopLogger()
@ -325,7 +325,7 @@ func newScrapePool(cfg *config.ScrapeConfig, app storage.Appendable, jitterSeed
func(l labels.Labels) labels.Labels { return mutateReportSampleLabels(l, opts.target) },
func(ctx context.Context) storage.Appender { return app.Appender(ctx) },
cache,
jitterSeed,
offsetSeed,
opts.honorTimestamps,
opts.sampleLimit,
opts.bucketLimit,
@ -775,7 +775,7 @@ func appender(app storage.Appender, sampleLimit, bucketLimit int) storage.Append
type scraper interface {
scrape(ctx context.Context, w io.Writer) (string, error)
Report(start time.Time, dur time.Duration, err error)
offset(interval time.Duration, jitterSeed uint64) time.Duration
offset(interval time.Duration, offsetSeed uint64) time.Duration
}
// targetScraper implements the scraper interface for a target.
@ -891,7 +891,7 @@ type scrapeLoop struct {
cache *scrapeCache
lastScrapeSize int
buffers *pool.Pool
jitterSeed uint64
offsetSeed uint64
honorTimestamps bool
forcedErr error
forcedErrMtx sync.Mutex
@ -1175,7 +1175,7 @@ func newScrapeLoop(ctx context.Context,
reportSampleMutator labelsMutator,
appender func(ctx context.Context) storage.Appender,
cache *scrapeCache,
jitterSeed uint64,
offsetSeed uint64,
honorTimestamps bool,
sampleLimit int,
bucketLimit int,
@ -1217,7 +1217,7 @@ func newScrapeLoop(ctx context.Context,
sampleMutator: sampleMutator,
reportSampleMutator: reportSampleMutator,
stopped: make(chan struct{}),
jitterSeed: jitterSeed,
offsetSeed: offsetSeed,
l: l,
parentCtx: ctx,
appenderCtx: appenderCtx,
@ -1238,7 +1238,7 @@ func newScrapeLoop(ctx context.Context,
func (sl *scrapeLoop) run(errc chan<- error) {
select {
case <-time.After(sl.scraper.offset(sl.interval, sl.jitterSeed)):
case <-time.After(sl.scraper.offset(sl.interval, sl.offsetSeed)):
// Continue after a scraping offset.
case <-sl.ctx.Done():
close(sl.stopped)

4
scrape/target_test.go
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@ -59,7 +59,7 @@ func TestTargetLabels(t *testing.T) {
func TestTargetOffset(t *testing.T) {
interval := 10 * time.Second
jitter := uint64(0)
offsetSeed := uint64(0)
offsets := make([]time.Duration, 10000)
@ -68,7 +68,7 @@ func TestTargetOffset(t *testing.T) {
target := newTestTarget("example.com:80", 0, labels.FromStrings(
"label", fmt.Sprintf("%d", i),
))
offsets[i] = target.offset(interval, jitter)
offsets[i] = target.offset(interval, offsetSeed)
}
// Put the offsets into buckets and validate that they are all

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