Amasterov/injection probability 17

[a-masterov]

We need to test SMGR failures.

This PR adds two features:
SMGR_API injection point in CHECK_FOR_INTERRUPTS – Injection can run even when there are no pending interrupts, and is gated by an inside_smgr_api counter for use by Neon’s SMGR layer.
Probability-based injection in the injection_points extension – New error-prob- action so injection points can raise an ERROR with a configurable probability (e.g. for fault-injection tests).

Reference: https://databricks.atlassian.net/browse/LKB-6690

[mmeent-databricks]

Same here: Can’t you install an SMGR that has these changes builtin, instead of modifying PG's code? It seems quite simple to me to have one that has these interrupts but otherwise lets that other SMGR resolve the requests.

[a-masterov]

Same here: Can’t you install an SMGR that has these changes builtin, instead of modifying PG's code? It seems quite simple to me to have one that has these interrupts but otherwise lets that other SMGR resolve the requests.

We need an arbitrary check for interrupts, not just an error in SMGR itself.
The changes in neon: https://github.com/databricks-eng/hadron/pull/4259/changes

[mmeent-databricks]

If you need arbitrary CFI, couldn't you use the hook that's already being installed?

See ProcessInterruptsCallback, which is called every time CHECK_FOR_INTERRUPTS calls into ProcessInterrupts().

It won't exactly always get called whenever execution reaches CFI, but you can mostly force that with e.g. a high-frequency timer, or by setting InterruptsPending in your callback.