[dev] Add INFO COMMANDSTATS tracking with per-command success rates

[Mathos1432]

Why is this change being made?

Garnet lacks Redis-compatible command usage statistics. Users and monitoring tools that rely on INFO COMMANDSTATS get no data, making it harder to understand workload composition and identify failing commands. This cherry-picks #1702 (merged to main) onto dev.

What changed?

• libs/server/Metrics/CommandStats.cs — New per-command statistics structure (calls, failed_calls, rejected_calls) array-indexed by RespCommand for O(1) access
• libs/server/Resp/RespServerSession.cs — Per-session command stats field, counter increments in ProcessMessages loop, commandErrorWritten flag for error detection, history handoff on dispose
• libs/server/Resp/RespServerSessionOutput.cs — WriteError overloads set commandErrorWritten flag
• libs/server/Resp/Objects/ObjectStoreUtils.cs — AbortWithErrorMessage sets commandErrorWritten flag
• libs/server/Metrics/GarnetServerMonitor.cs — History storage from disposed sessions, on-demand aggregation via Servers property, COMMANDSTATS reset support, dispose fix for when Start() was never called, resetEventFlags uses Enum.GetValues to fix pre-existing KeyNotFoundException
• libs/server/Metrics/GarnetServerMetrics.cs — globalCommandStats and historyCommandStats fields
• libs/server/Metrics/Info/GarnetInfoMetrics.cs — PopulateCommandStatsInfo with on-demand aggregation, canonical command names via RespCommandsInfo.GetRespCommandName()
• libs/server/Servers/GarnetServerOptions.cs — CommandStatsMonitor bool property
• libs/server/StoreWrapper.cs — Monitor creation includes CommandStatsMonitor and LatencyMonitor (fixes pre-existing NRE when only --latency-monitor enabled)
• libs/host/Configuration/Options.cs — --commandstats-monitor CLI flag
• libs/host/Configuration/Redis/RedisOptions.cs — commandstats-tracking Redis config alias
• libs/host/defaults.conf — CommandStatsMonitor default entry
• libs/common/Metrics/InfoMetricsType.cs — COMMANDSTATS enum value
• libs/server/SessionParseStateExtensions.cs — COMMANDSTATS parser case
• test/Garnet.test/RespCommandStatsTests.cs — 8 test cases covering disabled state, call tracking, failed calls, usec fields, multiple commands, success rate with periodic sampling, INFO SERVER status, Redis format
• test/Garnet.test/RespInfoTests.cs — Extended InfoSectionOptionsTest to validate all 6 excluded sections are absent from bare INFO
• test/Garnet.test/TestUtils.cs — commandStatsMonitor parameter for test server setup

How was this validated?

• All 12 new/updated tests pass on net8.0 and net10.0 (8 CommandStats + 4 InfoSection tests)
• BDN benchmarks show acceptable overhead: PING ~7.8%, SET/GET 0-4% (counter increments only, no Stopwatch)
• Existing test suite unaffected (CI green on Add INFO COMMANDSTATS tracking with per-command success rates #1702)
• Integration pipeline: [link]

[Copilot]

Pull request overview

Adds Redis-compatible INFO COMMANDSTATS support to Garnet, enabling per-command observability (calls / failed_calls / rejected_calls) with low overhead and opt-in tracking.

Changes:

• Introduces CommandStats data structure (array-indexed by RespCommand) and wires per-session tracking + history aggregation.
• Extends INFO plumbing to support a new COMMANDSTATS section (excluded from default INFO) and exposes enablement via CLI/config.
• Adds unit tests validating disabled behavior, call/failure tracking, formatting, and INFO section exclusions.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Garnet.test/TestUtils.cs	Adds commandStatsMonitor parameter to test server creation.
test/Garnet.test/RespInfoTests.cs	Extends INFO section exclusion assertions to include additional sections + Commandstats.
test/Garnet.test/RespCommandStatsTests.cs	Adds coverage for COMMANDSTATS output and tracking behavior.
libs/server/StoreWrapper.cs	Ensures GarnetServerMonitor is created when commandstats/latency monitors are enabled.
libs/server/SessionParseStateExtensions.cs	Adds parser support for COMMANDSTATS section token.
libs/server/Servers/GarnetServerOptions.cs	Adds CommandStatsMonitor option to server configuration.
libs/server/Resp/RespServerSessionOutput.cs	Marks commandErrorWritten when WriteError helpers are used.
libs/server/Resp/RespServerSession.cs	Adds per-session CommandStats and increments calls/failed/rejected counters.
libs/server/Resp/Objects/ObjectStoreUtils.cs	Marks commandErrorWritten for abort/error helper path.
libs/server/Metrics/Info/GarnetInfoMetrics.cs	Adds INFO COMMANDSTATS section generation + aggregation logic.
libs/server/Metrics/GarnetServerMonitor.cs	Adds history aggregation for commandstats, reset support, and Start/Dispose fix.
libs/server/Metrics/GarnetServerMetrics.cs	Adds global + history commandstats fields to global metrics.
libs/server/Metrics/CommandStats.cs	Implements the per-command counters and aggregation/reset helpers.
libs/host/defaults.conf	Adds default config entry for CommandStatsMonitor.
libs/host/Configuration/Redis/RedisOptions.cs	Adds commandstats-tracking config alias mapping.
libs/host/Configuration/Options.cs	Adds --commandstats-monitor CLI flag and wires it into server options.
libs/common/Metrics/InfoMetricsType.cs	Adds COMMANDSTATS enum value for INFO sections.

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