swactor/crates/runtime-dashboard/AGENTS.md

Runtime Dashboard — Agent Diagnostic Interface

Investigate Protocol

There is a line-oriented diagnostic protocol for programmatic runtime investigation. It reads text commands from stdin and writes JSON responses to stdout (one object per line). Human-readable output goes to stderr.

Launching

cargo run -p runtime-dashboard --example investigate_demo

Or programmatically against any running runtime:

use runtime_dashboard::investigate::run_investigate;
run_investigate(runtime_arc)?;   // blocks on stdin

Response Envelope

Every response is a single JSON object on one line:

{"ok": true,  "command": "overview", "data": { ... }}
{"ok": false, "command": "bogus",    "error": "unknown command `bogus` — try `help`"}

Commands

overview

Overall runtime summary.

→ overview
← {"ok":true,"command":"overview","data":{
     "workers": 4,
     "actors": 120,
     "total_messages_processed": 584210,
     "total_mailbox_depth": 37,
     "total_panics": 0,
     "total_type_mismatches": 0,
     "sends": {"local": 312000, "cross_worker": 271000, "inbox": 1210}
   }}

workers

All workers with per-worker counters.

→ workers
← {"ok":true,"command":"workers","data":[
     {"id":0,"actors":30,"mailbox_depth":12,"messages_processed":146000,
      "local_sends":78000,"cross_sends":67000,"inbox_sends":300,
      "type_mismatches":0,"panics":0},
     ...
   ]}

worker <id>

Single worker detail including tick-phase timing and its actors.

→ worker 2
← {"ok":true,"command":"worker","data":{
     "id": 2, "actors": 30, "mailbox_depth": 8,
     "messages_processed": 148000,
     "local_sends": 80000, "cross_sends": 67500, "inbox_sends": 500,
     "type_mismatches": 0, "panics": 0,
     "tick_phases": {
       "ticks": 412,
       "active_pct": 78.4,
       "avg_tick_us": 23.7,
       "phases_us": [120, 980, 7200, 90, 1100, 280],
       "phases_pct": [1.2, 10.0, 73.6, 0.9, 11.2, 2.9]
     },
     "actor_details": [
       {"address": "a1b2c3d4…", "mailbox_depth": 3, "last_msg_type": "MyMsg"},
       ...
     ]
   }}

The six tick phases (indices 0–5): 0. spawn_drain — draining spawn channel

1. transfer_drain — draining cross-worker transfer channel
2. tick_all — processing actor mailboxes (main work)
3. spawn_drain_2 — draining spawns created during tick
4. pending_local — delivering messages buffered within the worker
5. stats_publish — updating shared stat counters

actors [--sort mailbox|worker|address] [--limit N] [--worker W]

Actor listing with sorting, limit, and worker filter.

→ actors --sort mailbox --limit 5
→ actors --worker 0 --sort address
→ actors --limit 20

actor <hex_prefix>

Find actors whose address starts with the given hex prefix.

→ actor a1b2
← {"ok":true,"command":"actor","data":{
     "prefix": "a1b2",
     "matches": 1,
     "actors": [{"address": "a1b2c3d4…", "address_full": "a1b2c3d4...(64 hex chars)", "worker_id": 2, "mailbox_depth": 3, "last_msg_type": "MyMsg"}]
   }}

hot [N]

Top N actors by mailbox depth (default 10). Use this to find backpressure.

→ hot 5

phases [worker_id]

Tick-phase timing breakdown. Without an argument returns all workers.

→ phases
→ phases 2

diff <seconds>

Takes two snapshots separated by N seconds (max 30) and reports deltas. This is the primary throughput measurement tool.

→ diff 2
← {"ok":true,"command":"diff","data":{
     "elapsed_s": 2.001,
     "actors_before": 120, "actors_after": 132,
     "delta_messages": 8432,
     "msg_per_sec": 4213.9,
     "delta_local_sends": 4500,
     "delta_cross_sends": 3900,
     "mailbox_before": 37, "mailbox_after": 42,
     "per_worker": [
       {"worker_id": 0, "delta_messages": 2100, "msg_per_sec": 1049.5,
        "actors_before": 30, "actors_after": 33,
        "mailbox_before": 12, "mailbox_after": 14},
       ...
     ]
   }}

help

Returns all commands with usage strings.

quit

Exits the session.

Investigation Playbook

When diagnosing a runtime, a useful sequence:

1. overview — get the lay of the land
2. diff 2 — measure live throughput and detect growth
3. hot 10 — find actors with deepest mailboxes (backpressure)
4. workers — compare per-worker load distribution
5. worker <id> — drill into the busiest worker, check phase breakdown
6. phases — check if workers are spending time in unexpected phases
7. actors --worker <id> --sort mailbox — find hot actors on that worker
8. actor <prefix> — get full address and type for a specific actor

Key Metrics to Watch

Symptom	Check	Meaning
High mailbox_depth	hot 10	Actor can't keep up — backpressure
Uneven msg_per_sec across workers	diff 2 per_worker	Load imbalance
High cross_sends vs local_sends	overview sends	Actors that talk are on different workers
active_pct near 100%	phases <id>	Worker is saturated
High phase 1+4 % vs phase 2	phases <id>	Delivery overhead dominates processing
Growing actors_after vs actors_before	diff 5	Unbounded actor spawning
type_mismatches > 0	overview	Messages routed to wrong actor type
panics > 0	overview	Actor handlers are panicking