refactor(Alerts.Sort): more performant comparison#3311
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thecristen
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Jul 1, 2026
| next_active_period_active_time(rest_of_active_periods, time) | ||
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| # period hasn't ended yet, but no defined start time -- use the current time | ||
| is_nil(start_time) -> |
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Some of our tests have alerts involving active periods with a nil start time, so I added this clause to handle those. I'm not sure if this'll ever be encountered in real alerts from Alerts Manager, though.
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I'm glad I saw this PR, I have one open with yet a 3rd way of computing the active time period. I'm going to put mine into draft for now. I saw this exact same behavior regarding only our tests having nil start times, thanks for following up with the transit data team about if that's even possible.
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Scope
While tackling #3310 I noticed that
Alerts.Sort.sort/2was featuring prominently in my flame charts, and I wanted to see if I could do anything about that.Implementation
First of all.
/stops/<mode>pages don't even show alerts. So the first commit moves the call which assigns alerts toconnto the specific method behind rendering the individual stop pages, instead of being invoked for every page handled byDotcomWeb.StopController.Then when debugging
Alerts.Sort.sort/2, I noticed the sorting logic included assessing the next active period start time. And I remembered we'd later implemented a different function for computing that, over atDotcom.Alerts.StartTime.next_active_time/2! So I wanted to see if reusing that was more performant (and looks like it is!).These charts were generated from loading South Station page with an already warmed cache.
How to test
We could verify if the subway Planned Work section still sorts those alerts in the same way as before.