fix(alert): Delete IncidentTrigger as child of AlertRuleTrigger

[kcons]

There can be 10s-100s of thousands of IncidentTrigger rows associated with an AlertRuleTrigger.
In SENTRY-4A76, we see repeated failed attempts to delete an AlertRuleTrigger with 15k IncidentTriggers, and this change will hopefully help there.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Additional details and impacted files

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+ Misses      72896     72890    -6     
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[ceorourke]

I wonder if we instead change the order here https://github.com/getsentry/sentry/blob/master/src/sentry/deletions/defaults/alertrule.py#L15 to have Incident first that would delete the IncidentTrigger objects before getting to AlertRuleTrigger

[kcons]

I wonder if we instead change the order here https://github.com/getsentry/sentry/blob/master/src/sentry/deletions/defaults/alertrule.py#L15 to have Incident first that would delete the IncidentTrigger objects before getting to AlertRuleTrigger

I think it would, but we'd probably still not want to rely on cascades, and I think we don't index IncidentTrigger by incident id, so that path would likely be pretty slow.

[ceorourke]

I wonder if we instead change the order here https://github.com/getsentry/sentry/blob/master/src/sentry/deletions/defaults/alertrule.py#L15 to have Incident first that would delete the IncidentTrigger objects before getting to AlertRuleTrigger

I think it would, but we'd probably still not want to rely on cascades, and I think we don't index IncidentTrigger by incident id, so that path would likely be pretty slow.

It is indexed https://github.com/getsentry/sentry/blob/master/src/sentry/incidents/models/incident.py#L322 but I'm ok with trying it on the AlertRuleTrigger 👍