Autocomplete of metric names on /graph UI is much slower on 2.7 vs. 2.2

[allengeorge]

I just upgraded one of our internal Prometheus servers from 2.2 to 2.7. After the upgrade I noticed that autocomplete has slowed down dramatically: typing a letter causes a multi-second - often 10s of seconds - lag before matches show up, and it takes another multi-second lag till I can select a metric. I looked at #3321, but decided to create a new issue because it feels like a regression (i.e. 2.2 was noticeably faster).

This behavior exhibits on both Chrome/Firefox.

We are running Prom on Kube using Helm.

[brian-brazil]

How many metric names do you have?

[simonpasquier]

I did a quick scan and couldn't find any obvious change between 2.2 and 2.7 that would explain the regression. In any case, #5139 should fix this problem.

[simonpasquier]

Closing as #5139 got merged.