Improve autocomplete performance after `#`

See epic for details, specifically around &2832 (comment 302732107).

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@donaldcook per https://gitlab.com/gitlab-org/plan/-/issues/85#note_321008586 I've added this to 13.0, lets get it weighted!

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@kushalpandya is this issue still valid or can it be closed?

@amandarueda This is very much a concern, and is something that we can improve and have benefits available across legacy Issuables as well as Work Items, I'd even track this as a part of https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/1467?iid_path=true.

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@amandarueda - please see the following guidance and update this issue.

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added typebug label

@kushalpandya, @amandarueda and groupproduct planning Software Engineer in Test,

This groupproduct planning bug has at most 50% of the SLO duration remaining and is an SLONear Miss breach. Please consider taking action before this becomes an SLOMissed in -1013 days (2020-06-08).

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I did some network request inspection here, and for gitlab-org/gitlab project, we're fetching all the open issues with their iid, title, and id, over 50k issues that is, and thus, request takes ~8 seconds and downloads about 4.9 MB of payload. However, once this list is loaded, it is cached as long as page is not reload so successive searches are faster because the frontend does it locally. which IMO is quite fast for the size of data we're fetching here.

The endpoint in question here is /gitlab-org/gitlab/-/autocomplete_sources/issues and it doesn't support page size or page number IIRC, so there are two possible approaches we can take to fix it this;

Backend + Frontend

Update /autocomplete_sources/* endpoints to support params like page_size, page (i.e. number), search (that accepts characters typed).

Only drawback here is that every key-stroke would cause a network request (unless it was already made and cached), so depending on network conditions, it can be fast or slow.

Frontend only

If we know usage for # is high, then we can proactively fetch the response and cache in the browser (either in localStorage or IndexedDB), and perhaps periodically refresh it. This would ensure that autocompletion results are loaded instantly. This can be done as an extension of #386275.

Obvious drawback here is the lack of real-time data, where the user may not have a newly created issue showing up in autocompletion and would have to wait for background refresh to complete.

mentioned in issue #225842 (closed)

marked #225842 (closed) as a duplicate of this issue

marked this issue as related to #225842 (closed)

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