We had an outage on a Jira instance running JSD 3.16.11 today which appeared to be caused by requests to the `/jira/rest/internal/2/user/mention/search` endpoint.
Looking at request times for different queries, those that do NOT contain a query string appear to be significantly slower.
Note the scale change - the longest with a query string was 13s, the shortest without was 28s, with longest over 60s
- With a query string, took 0.14s: /jira/rest/internal/2/user/mention/search?issueKey=KEY-5678&maxResults=10&query=il&_=1587494420052, (referrer is /jira/browse/KEY-5678)
- Without a query string, took 62s: /jira/rest/internal/2/user/mention/search?issueKey=KEY-1234&maxResults=10&_=1587407226218 (referrer is /jira/browse/KEY-1234?filter=-1)
I am not sure what this endpoint is - I went into the referrer (for a lot of them this was filter=-1) and clicked around but was not able to hit that endpoint with anything I did.
Searches return promptly with no performance impact.
This actually caused an outage for us due to a spike in CPU which seems connected to GC activity.
Currently there is no known workaround for this behavior. A workaround will be added here when available