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Replay storage costs

VoiceGateway’s conversation replay captures every STT chunk, LLM token, TTS frame, and conversation-state snapshot for every session. This page surfaces the on-disk storage cost so the trade-off between fidelity and footprint is visible before you set per-project retention.

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What gets stored

Four tables per the migration 0004 schema:
TableRow payloadTypical row size
replay_stt_eventsJSON: text, is_final, alternatives100 - 400 bytes
replay_llm_tokensJSON: token_text, role, is_tool_invoke, tool_args_partial80 - 200 bytes
replay_tts_framesJSON: frame_duration_ms, underrun, voice_id80 - 120 bytes
replay_state_snapshotsJSON: system_prompt, message_history, tool_call_in_flight, structured_output_collected500 - 5000 bytes (depends on prompt + history size)
Every row also carries the boilerplate: id, session_id, t_ms, provider, cost_usd, created_at. Add roughly 80-120 bytes of column overhead per row. Indexes on (session_id, t_ms) add another 30-50% of payload size.

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Per-minute estimate

For a typical voice conversation (caller speaks for half the time, agent for half, normal-cadence LLM with a 500-token system prompt):
ModalityEvents per minuteBytes per minute
STT (partials + finals)30 - 608 KB - 24 KB
LLM tokens200 - 50030 KB - 80 KB
TTS frames (20-50ms each)600 - 150060 KB - 180 KB
State snapshots (1/sec cap)6030 KB - 300 KB
Total: roughly 130 KB - 580 KB per minute of conversation, with the floor for short crisp exchanges and the ceiling for chatty agents with long conversation histories. The design target of 30-100 KB/min is achievable on the floor; realistic agents will land closer to the ceiling. If you find yourself trending above 500 KB/min consistently, the per-project replay.enabled: false toggle is the fastest mitigation.

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Worked example

A solo developer running 100 voice calls per day, averaging 5 minutes each: 
100 calls/day × 5 min/call × 200 KB/min = 100,000 KB/day ≈ 100 MB/day
At the default 90-day retention: 
100 MB/day × 90 days ≈ 9 GB total replay storage
At AWS S3 standard storage prices (~$0.023/GB-month): 
9 GB × $0.023 ≈ $0.21/month
On the local SQLite database (no cloud markup), the cost is the disk byte cost: ~0.01/GB−monthonadeveloperSSD≈ 0.01/GB-month on a developer SSD ≈ ~0.09/month for the same 9 GB. A team agency running 10,000 conversations per day at 3 minutes average scales linearly: ~3 TB at 90-day retention, ~70/monthonS3standardor 70/month on S3 standard or ~30/month on local disk. At that point the retention_days knob matters: dropping to 30 days cuts storage to one-third.

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Tuning knobs

Three per-project knobs in voicegw.yaml’s replay: block influence storage:
KnobDefaultEffect
enabledtrueCapture for every session. Set false to skip capture entirely.
retention_days90Age replay rows out after this window. Lower to reduce footprint linearly.
flush_size_events500Batched writes; smaller writes more often, larger holds more memory. No storage effect.
buffer_size_events5000In-memory cap. Above this, oldest events are dropped with a counter. The dashboard surfaces dropped events as “events dropped here” rather than silently misleading the developer.
The enabled toggle is the binary on/off. The retention_days knob is the gradient lever. The buffer_size_events and flush_size_events knobs trade off memory pressure and write batching but do not change long-term storage volume.

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Dashboard storage view

GET /api/replay/storage returns per-project replay byte totals. The dashboard surfaces this as a breakdown so the developer sees the cost in real time: 
{
  "total_replay_size_bytes": 9234567890,
  "by_project": [
    {"project": "acme", "replay_size_bytes": 8000000000},
    {"project": "default", "replay_size_bytes": 1234567890}
  ]
}
A future follow-up will surface this in a sidebar panel on the dashboard with cost-per-month estimates inline.