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lib/storage: add a comment to indexSearch.containsTimeRange() on why it allows false positives

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Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2239
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Aliaksandr Valialkin 2022-02-24 12:47:24 +02:00
parent a16f1ae565
commit 8bf3fb917a
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1 changed files with 6 additions and 1 deletions
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7
lib/storage/index_db.go
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@ -1868,7 +1868,12 @@ func (is *indexSearch) containsTimeRange(tr TimeRange) (bool, error) {
ts := &is.ts
kb := &is.kb
// Verify whether the maximum date in `ts` covers tr.MinTimestamp.
// Verify whether the tr.MinTimestamp is included into `ts` or is smaller than the minimum date stored in `ts`.
// Do not check whether tr.MaxTimestamp is included into `ts` or is bigger than the max date stored in `ts` for performance reasons.
// This means that containsTimeRange() can return true if `tr` is located below the min date stored in `ts`.
// This is OK, since this case isn't encountered too much in practice.
// The main practical case allows skipping searching in prev indexdb (`ts`) when `tr`
// is located above the max date stored there.
minDate := uint64(tr.MinTimestamp) / msecPerDay
kb.B = is.marshalCommonPrefix(kb.B[:0], nsPrefixDateToMetricID)
prefix := kb.B