ottyl/tickets/026-max-logs-in-memory.md

026 — Settings: maximum logs kept in memory

Summary

ottyl currently keeps every ingested log forever in the in-memory BTreeMap. The wishlist wants a settings-configurable cap on how many logs are retained, with no cap (unlimited) as the default.

Scope

• New Settings field (e.g. max_logs: Option<usize>), None/unset = unlimited, matching the existing "by default it should be unlimited" requirement.
• Enforce the cap in the engine's ingest path: once the IngestedLog range exceeds the configured max, evict the oldest entries (lowest sequence) to bring it back under the cap.
• Decide and document what happens to data that references evicted logs:
  • Params/metrics already derived into Bucket values from an evicted log are not retroactively removed (buckets are aggregate data, not raw logs) — state this explicitly so it's not treated as a bug later.
  • sequence numbering does not reset/renumber on eviction.
• Expose the setting in the Settings API/NavMenu settings panel (a numeric input, clearable back to "unlimited").

Acceptance criteria

• With no cap configured, behavior is unchanged (unbounded retention, as today).
• Setting a cap and ingesting past it keeps memory usage bounded — oldest logs are evicted, newest max_logs remain queryable via GET /api/logs.
• Changing the cap at runtime (via settings) takes effect on the next ingest without requiring a restart.

Depends on

None — extends the existing Settings model.