feat(mcp): HTTP streamable robustness for frequent queries#55
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Adds four robustness measures to the MCP server so frequent agent-side polling doesn't cripple it under load: 1. Concurrency limit. Counting semaphore (default 32 in-flight) gates tools/call. Beyond the cap, callers receive JSON-RPC error -32000 "server overloaded" so well-behaved clients back off. 2. Per-call timeout. Default 30s deadline applied to every tools/call. Past it the handler returns JSON-RPC error -32001 "call timeout" and frees its slot. 3. Result cache. A small TTL cache (default 5s) memoizes the cheap in-memory GraphRAG tools (get_service_map, impact_analysis, root_cause_analysis, get_anomaly_timeline, get_service_health), keyed by (tenant, tool, args). Cache keys are tenant-scoped so two tenants don't collide; arg-map order is normalized so the same query hits regardless of client serialization quirks. 4. SSE keep-alive. The GET /mcp stream now emits a `: keep-alive\n\n` comment every 25s so reverse proxies (nginx/Envoy/Istio) don't time out idle MCP connections. Without this, low-update-rate workloads reliably hit "connection reset" mid-session. New env vars (all opt-out via 0): MCP_MAX_CONCURRENT (32), MCP_CALL_TIMEOUT_MS (30000), MCP_CACHE_TTL_MS (5000). Tests: 11 unit tests covering overload rejection, no-cap path, timeout abort, cache hit/miss, tenant isolation, arg-order stability, TTL disable, SSE event-shape, and Stats counters. Docs updated. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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This was referenced Apr 28, 2026
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Five small follow-ups from the second-pass review of PRs #49–#55: - tsdb: fire cardinality-overflow callback AFTER releasing the Aggregator mutex. The callback is currently a Prometheus increment (atomic) but holding mu across an external function call is a footgun for any future hook. Capture the tenant under lock; invoke after Unlock. - storage: use errors.Is(err, sql.ErrNoRows) in pgLogsRelkind instead of strings.Contains(err.Error(), "no rows"). Robust against driver wrapping. - storage: convert Repository.logsPartitioned from plain bool to atomic.Bool. Removes the memory-model fragility of "the writer ran first" — read by retention.go from a separate goroutine. - config: reject negative MCP_MAX_CONCURRENT / MCP_CALL_TIMEOUT_MS / MCP_CACHE_TTL_MS at Validate(). 0 stays the documented "disable" sentinel; negatives are typos that should fail loud. - mcp: upgrade SetCallLimit doc to flag it startup-only — runtime resize leaks a slot in the old channel. Skipped (with rationale, not silently dropped): - M1 Submit TOCTOU on closed pipeline — cosmetic only, current ordering is documented. - M2 ring/onIngest setter races — would require API change to fix properly; benign during normal startup-only usage. - M4 FTS5 trigger throughput — needs a bulk-rebuild path, not a one-line tweak. - M5 isQueueFull scope — hypothetical concern with no observed symptom; revisit only if metrics show drift. Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Four robustness measures so frequent agent polling doesn't cripple the MCP server:
tools/call. Past the cap → JSON-RPC-32000server-overloaded.-32001call-timeout, slot is freed.get_service_map,impact_analysis,root_cause_analysis,get_anomaly_timeline,get_service_health). Keyed by(tenant, tool, args)with tenant-isolation and arg-order normalization.: keep-alive\n\ncomment every 25s so reverse proxies (nginx/Envoy/Istio) don't time out idle MCP streams.Why
Phase 6 of the 7-day-retention robustness initiative — the user's explicit ask "MCP HTTP streamable needs to be robust for frequent queries". Without these, sustained agent-side polling at >32 concurrent calls degrades GraphRAG, slow tool handlers wedge slots indefinitely, and idle SSE connections die behind reverse proxies.
Configuration (env, all opt-out via 0)
MCP_MAX_CONCURRENT32MCP_CALL_TIMEOUT_MS30000MCP_CACHE_TTL_MS5000Test plan
go test ./... -race -short -count=1— full suite greenTestRobustness_ConcurrencyLimit_OverloadsBeyondCap— verifies-32000and counterTestRobustness_ConcurrencyLimit_NoCapWhenDisabled— verifiesSetCallLimit(0)is no-opTestRobustness_CallTimeout_AbortsLongRunningCall— verifies deadline ctx firesTestRobustness_CacheHit_ServesFromCache— verifies pre-seeded result returns andCacheHitsincrementsTestRobustness_CacheKey_TenantIsolated— same(tool, args)across tenants → distinct keysTestRobustness_CacheKey_StableAcrossArgOrder— JSON map order does not affect the keyTestRobustness_NonWhitelistedToolNotCached— cache whitelist is enforcedTestRobustness_CacheTTLDisabled—SetCacheTTL(0)truly disablesTestRobustness_SSEHeartbeat_KeepsConnectionAlive— verifies initialevent: endpointand content-typeTestRobustness_StatsCounters_Increment— verifies counter movement on overloadgolangci-lint run --new-from-rev=origin/main— clean🤖 Generated with Claude Code