Checkout liveness: use TinyTDS #ping from active? (follow-up to #1396)

[emailrhoads]

Summary

Idle TCP RST (TCP reset: peer or middlebox abruptly closes the socket while the client still believes the session is alive) leaves FreeTDS dbdead / TinyTDS active? stale-true until the next real I/O. Rails 8 verify! then hands out a half-dead checkout. The next statement can hang for the connection’s full FreeTDS statement timeout (often minutes) before failing with something like Adaptive Server connection timed out.

This is the checkout-liveness half of #1396. Exception mapping (DBPROCESS is dead… → ConnectionNotEstablished) was addressed in #1397 / 8.0.11; detecting the dead handle before the real query still needs a bounded round-trip.

Rails / adapter context

• Postgres and Trilogy still probe in active? today (query ";" / #ping).
• This adapter used to run raw_connection_do "SELECT 1" in active? until #1121 (Oct 2023) switched to passive TinyTDS active?.
• A naive return to SELECT 1 would restore probing but hang on the connection’s multi-minute FreeTDS timeout when the socket is already dead. The probe needs a short FreeTDS DBSETTIME, not Ruby Timeout (which does not reliably interrupt TinyTDS/C I/O).

Proposed split

Layer	Responsibility	PR
tiny_tds	Driver primitive: Client#ping(timeout:) + query_timeout= (temporary short DBSETTIME, SELECT 1, restore on success; false on failure)	rails-sqlserver/tiny_tds#609
activerecord-sqlserver-adapter	Policy: call #ping from active? when available; :ping_timeout (default 2s, 0 disables); fallback to passive active? on older TinyTDS	rails-sqlserver/activerecord-sqlserver-adapter#1412

Ask for maintainers

Please take a look at both PRs. tiny_tds appears lightly maintained right now, and without a reviewed #ping (or equivalent) the adapter cannot match Postgres/Trilogy checkout behavior without reintroducing long hangs. Adapter #1412 is ready to consume #ping once tiny_tds#609 lands (or guidance on an alternate driver API).

Happy to adjust either PR based on preferred defaults, naming, or whether ping should live only behind verify! vs every active?.

Related

• #1396 — idle RST + passive dbdead / active?
• #1121 — removed SELECT 1 from active?
• tiny_tds#609 — Client#ping(timeout:)
• adapter#1412 — use #ping from active?