perf(prometheus): optimize duplicate metric splitting to O(N) complexity #1383
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Pull request overview
This PR optimizes the Prometheus parser's metric splitting algorithm to reduce time complexity from O(N*M) to O(N) where N is the buffer size and M is the number of metric chunks. The optimization replaces repeated bytes.Index calls with a single-pass scan using bytes.IndexByte to quickly locate potential delimiters.
- Replaces dual
bytes.Indexcalls per iteration with efficientbytes.IndexBytescanning - Adds logic to skip current delimiter when positioned at one, ensuring forward progress
- Improves performance for large Prometheus metric payloads with many duplicate metrics
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| p := bytes.IndexByte(rest[scanOffset:], '#') | ||
| if p == -1 { | ||
| idx = -1 | ||
| break | ||
| } | ||
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| // Potential delimiter found at relative index (scanOffset + p) | ||
| candidate := rest[scanOffset+p:] | ||
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| // Verify if it is indeed a header | ||
| if bytes.HasPrefix(candidate, helpHeader) || bytes.HasPrefix(candidate, typeHeader) { | ||
| idx = scanOffset + p | ||
| break | ||
| } | ||
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| // False alarm (e.g. '#' inside a label or comment), continue scanning | ||
| scanOffset += p + 1 |
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The variable name 'p' conflicts with the Parser receiver variable in the method signature. While this is scoped within the for loop, it reduces readability and could be confusing. Consider using a more descriptive name like 'hashPos' or 'pos' instead.
Suggested change
| p := bytes.IndexByte(rest[scanOffset:], '#') | |
| if p == -1 { | |
| idx = -1 | |
| break | |
| } | |
| // Potential delimiter found at relative index (scanOffset + p) | |
| candidate := rest[scanOffset+p:] | |
| // Verify if it is indeed a header | |
| if bytes.HasPrefix(candidate, helpHeader) || bytes.HasPrefix(candidate, typeHeader) { | |
| idx = scanOffset + p | |
| break | |
| } | |
| // False alarm (e.g. '#' inside a label or comment), continue scanning | |
| scanOffset += p + 1 | |
| hashPos := bytes.IndexByte(rest[scanOffset:], '#') | |
| if hashPos == -1 { | |
| idx = -1 | |
| break | |
| } | |
| // Potential delimiter found at relative index (scanOffset + hashPos) | |
| candidate := rest[scanOffset+hashPos:] | |
| // Verify if it is indeed a header | |
| if bytes.HasPrefix(candidate, helpHeader) || bytes.HasPrefix(candidate, typeHeader) { | |
| idx = scanOffset + hashPos | |
| break | |
| } | |
| // False alarm (e.g. '#' inside a label or comment), continue scanning | |
| scanOffset += hashPos + 1 |
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