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optimize to posting group label value matching #7343
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Signed-off-by: Ben Ye <benye@amazon.com>
pkg/store/bucket.go
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@@ -2726,7 +2726,7 @@ func matchersToPostingGroups(ctx context.Context, lvalsFn func(name string) ([]s | |||
// Merge PostingGroups with the same matcher into 1 to | |||
// avoid fetching duplicate postings. | |||
for _, val := range values { | |||
pg, vals, err = toPostingGroup(ctx, lvalsFunc, val) | |||
pg, vals, err = toPostingGroup(ctx, lvalsFunc, val, len(values) == 1) |
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Why do we need to check for len(values) == 1
?
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I think the difference we have with prometheus/prometheus#13958 is that we cache results of label values. So we cannot reuse vals
only if it is the last value we have. I have updated the condition.
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I am actually a little bit unsure now if it reuses the values array causes any issue or not.
Updated: OK I think it is not safe to reuse the values other than reusing it once at the last value.
Changes
The optimization comes from prometheus/prometheus#13958 and https://github.com/prometheus/prometheus/blob/main/tsdb/querier.go#L358.
With latest Prometheus regex matcher optimization, now empty value
""
is optimized intoemptyStringMatcher
which only checks the value length https://github.com/prometheus/prometheus/blob/main/model/labels/regexp.go#L325.Since label values should be always non empty, we can optimize some cases to not run matching at all.
Verification