Paginate the notes incremental fetch endpoint
What does this MR do?
This is an extraction from !33619 (closed) , which contains (rudimentary) frontend + backend changes.
Returning an unlimited number of elements from any endpoint is a bad idea. For the notes endpoint specifically, we return all notes since a given X-Last-Fetched-At value. The backend specifies the new value to use for that item in the response, so if we return a limited set of notes and use an appropriate value, we get a rudimentary form of keyset pagination for free.
The way the notes endpoint is used today, this is mostly a theoretical worry, and in practice, basically every response will fit within a single page anyway. However, we can use the notes endpoint instead of the discussions endpoint to fill a merge request discussion from the beginning of time. When we do this, large discussions are loaded in batches automatically, using pre-existing frontend code. So this change is best seen as preparatory work for removing discussions altogether.
This commit also fixes a pre-existing problem with the endpoint, which is the fact that updated_at is stored with microsecond precision in the database. Converting the X-Last-Fetched-At value from integer to float allows us to avoid a range of boundary conditions that result from the difference in resolution between the two levels.
Screenshots
No FE-visible changes, but here's a screenshot of some incrementally-added notes in an MR to demonstrate that the functionality continues to work:
Does this MR meet the acceptance criteria?
Conformity
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Changelog entry - [-] Documentation (if required)
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Code review guidelines -
Merge request performance guidelines -
Style guides -
Database guides - [-] Separation of EE specific content
Availability and Testing
If a very large number of notes is created within a short period, they'll take slightly longer to be shown in the frontend. However, you won't have finished reading the first 50 new notes before the next batch comes in.
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Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process. -
Tested in all supported browsers - [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done
Part of #217673 (closed)