pgbench: Add --percentile option for latency percentile reporting #821
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This commit adds a new --percentile option to pgbench that reports latency percentiles (p50, p90, p99, p99.9) when enabled. The implementation uses a histogram-based approach with: - Fine-grained buckets (0-100ms at 100μs resolution) - Coarse buckets (100ms-10s at 1ms resolution) - Bounded memory usage (~85KB per thread per script) This provides accurate percentile calculations without storing all individual latency measurements. Changes: - Added LatencyHistogram structure and related functions - Added --percentile command-line option - Updated help text and documentation - Added comprehensive test coverage
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pgbench: Add --percentile option for latency percentile reporting
Add support for computing and reporting latency percentiles (p50, p90, p99,
p99.9, p99.99) in pgbench using a memory-efficient histogram approach.
The existing stddev calculation uses a streaming algorithm that maintains
only sum and sum-of-squares, which cannot compute percentiles. This commit
adds an optional log-linear histogram that tracks the distribution of
latency values with bounded memory.
Histogram Design:
Memory Efficiency:
Features:
Usage:
pgbench --percentile -t 1000 -c 10 dbname
Output includes:
latency percentile 50 = X.XXX ms
latency percentile 90 = X.XXX ms
latency percentile 99 = X.XXX ms
latency percentile 99.9 = X.XXX ms
latency percentile 99.99 = X.XXX ms
TAP tests added to verify percentile output in single-threaded,
multi-threaded, and per-script scenarios.