RFR: 1682: PullRequestBot::getPeriodicItems takes too long

[Zhao Song]

On Thu, 17 Nov 2022 22:57:25 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> Similar to the NotifyBot in [SKARA-1680](https://bugs.openjdk.org/browse/SKARA-1680), the PullRequestBot is also suffering from spending a very long time in the very first round of getPeriodicItems after a bot restart. The last time we redeployed this bot, it took ~40 minutes. This was long enough to trigger several users to ask if Skara was having issues.
> 
> The cause is similar. There is an `isReady` call for each PR, which checks for comments. The comment checking here is even worse than for the NotifyBot because every PR is checked for comments, not just those that match the "rfr" or "integrated" labels.
> 
> My proposed solution is similar. We need to move this expensive evaluation to the relevant WorkItems where they can run concurrently instead of serially in `getPeriodicItems`. I chose to make the call from the abstract superclass `PullRequestWorkItem`. This does add the check unnecessarily to the `LabelerWorkItem`, but that one is running so rarely that I don't think it matters performance wise. For correctness, I don't think it hurts checking an extra time.

LGTM, just a small question, what don't we move `isReady()` to `PullRequestWorkItem`?

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Marked as reviewed by zsong (Committer).

PR: https://git.openjdk.org/skara/pull/1423