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bab4c1e19b
GET /printers/{id}/cover took its printer row via Depends(get_db), whose
yield-dependency session stays open for the whole request — including the
3MF cover download (up to 8 remote paths x retries with backoff, minutes
under FTP contention). One pooled connection sat idle-in-transaction the
entire time; on a large farm a wall of dashboards drained the pool. The
route now fetches the printer in a short-lived async_session() and releases
the connection before the download (expire_on_commit=False keeps printer.*
readable). Pinned by a signature-inspection guard that fails if get_db is
ever re-added.
fix(print-start): release the DB connection across plate detection and 3MF download (#2572)
on_print_start held one session from top to bottom of the handler, across
two slow I/O blocks that need no database: the plate-detection camera grab
and, on the new-archive path, the multi-path 3MF FTP download (its own
comments cite worst cases of tens of minutes). The connection sat idle-in-
transaction for both, once per starting print. It now commits at each
boundary — only read SELECTs have run on those paths (every write branch
returns earlier), so the commit persists nothing and simply returns the
connection to the pool for the I/O; the next query re-acquires, and
expire_on_commit=False keeps printer.* readable.
fix(startup): connect to printers concurrently so the API serves within seconds (#2572)
init_printer_connections awaited each printer's connection serially, and
connect_printer ends in a fixed 1s settle wait. The MQTT connect is non-
blocking (connect_async + loop_start), so that 1s x fleet size was pure
serial dead air the FastAPI lifespan blocked on before uvicorn began
serving — ~100s before port 8000 responded on a 93-printer farm. The
connections are now started with asyncio.gather, so the step takes ~1s
regardless of fleet size. return_exceptions=True isolates each result: one
unreachable printer no longer aborts the rest, or startup itself.