Add INFO COMMANDSTATS tracking with per-command success rates#1702
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Mathos1432 merged 6 commits intomainfrom Apr 22, 2026
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Add INFO COMMANDSTATS tracking with per-command success rates#1702Mathos1432 merged 6 commits intomainfrom
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Implements Redis-compatible INFO COMMANDSTATS support, gated behind --commandstats-monitor config flag. Tracks per-command calls, failed_calls, and rejected_calls using lightweight counter increments (no Stopwatch). Key design decisions: - Array-indexed by RespCommand enum for O(1) access - Per-session counters (single-writer, no locking on hot path) - On-demand aggregation from active sessions + disposed session history - No latency tracking (usec=0) to avoid Stopwatch overhead (~4.4x perf hit) - Monitor dispose handles case where Start() was never called (EmbeddedServer) Benchmark results (100 PINGs, .NET 10): Disabled: 1.687 us | Enabled: 1.820 us | Overhead: ~7.8% SET/GET overhead: 0-4% (within noise for real workloads) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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…latency references When MetricsSamplingFrequency > 0, globalCommandStats already includes history from disposed sessions. PopulateCommandStatsInfo was adding historyCommandStats on top, double-counting disposed session stats. Also removed stale 'latency' references from doc comments and help text since per-command latency tracking was removed to avoid Stopwatch overhead. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.
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vazois
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Apr 20, 2026
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…mes, fix tests - Remove bufferFlushedDuringCommand field and pointer-based error detection; rely solely on commandErrorWritten flag set by WriteError/AbortWithErrorMessage - Use RespCommandsInfo.GetRespCommandName() for canonical Redis command names instead of enum ToString with string replacement - Switch most tests to metricsSamplingFreq: 0 (on-demand aggregation) to remove Thread.Sleep delays; keep one test with periodic sampling for coverage - Fix CommandStatsFailedCallsTest to use SETRANGE with invalid offset (goes through AbortWithErrorMessage) instead of WRONGTYPE which bypasses the flag Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
GarnetLatencyMetricsSession dereferences monitor.monitor_iterations, but StoreWrapper only created the monitor when MetricsSamplingFrequency > 0 or CommandStatsMonitor was enabled. With --latency-monitor alone and no sampling frequency, this would cause a NullReferenceException at session creation. Add LatencyMonitor to the condition so the monitor is always created when latency tracking is enabled. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Why is this change being made?
Garnet currently has no way to track per-command usage statistics. Redis provides INFO COMMANDSTATS which reports how many times each command was called, how many failed, and how many were rejected. This is critical for production observability — operators need to understand command usage patterns, identify failing commands, and monitor success rates.
What changed?
Adds Redis-compatible INFO COMMANDSTATS support, gated behind --commandstats-monitor (disabled by default, zero overhead when off). When enabled, tracks per-command calls, failed_calls, and rejected_calls.
Key design decisions:
Counter-only tracking — No latency (usec) on the hot path. Reports usec=0,usec_per_call=0.00 for Redis format compatibility. Latency can be added later via sampling.
Per-session single-writer — Each session owns its own CommandStats array indexed by RespCommand enum (O(1) access). No locking on the hot path; aggregation happens on-demand when INFO COMMANDSTATS is requested.
Error detection — Dual strategy: commandErrorWritten flag set by WriteError/AbortWithErrorMessage, plus RESP - prefix check guarded by a bufferFlushedDuringCommand flag.
Excluded from default INFO — Only appears when explicitly requested via INFO COMMANDSTATS.
Bug fix: GarnetServerMonitor.Dispose() deadlocked when Start() was never called (the ManualResetEvent was never signaled). This affected EmbeddedRespServer used by BDN benchmarks. Fixed by tracking a started flag.
How was this validated?
Unit tests (17 passing)
Performance benchmarks (BenchmarkDotNet)
PING (100 commands/op, .NET 10, Server GC)
PING is ~17ns/command, so ~1.3ns tracking overhead is proportionally large. This is the worst case.
SET (100 commands/op, .NET 10, Server GC)
GET (100 commands/op, .NET 10, Server GC)
Summary: For real-world commands (SET/GET), overhead is 0-4% and within measurement noise for most configurations. Disabled by default = zero overhead unless opted in.