Three related performance fixes for slow (>500ms) API responses.
1. Stop blocking the event loop. Route handlers were declared `async def`
but ran synchronous SQLAlchemy queries (and synchronous Redis calls via
the cache decorator) directly on the event loop, serializing requests.
Convert all handlers to sync `def` so FastAPI runs them in its
threadpool, and make the `@cached` decorator dual-mode (sync wrapper for
sync handlers, async wrapper preserved for a future async/Postgres path).
2. Tune SQLite for concurrency. Enable WAL, busy_timeout and
synchronous=NORMAL on every connection, and size the pool above the
threadpool so handlers don't wait on connections. In-memory SQLite is
guarded (no overflow-pool kwargs).
3. Precompute an indexed `nodes.is_observer` flag. The `observer=true`
filter scanned ~68k+ event rows to find a handful of observers (the
advertisements page calls it with limit=500). Replace the 5-way OR of
subqueries with `WHERE nodes.is_observer = ?`. The collector sets the
flag on first observation (in add_event_observer); the cleanup job
clears it once a node's events are all pruned; a migration adds the
column/index and backfills from the existing union.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Louis King