perf: add new index to serve a full WHERE clause

[miaulalala]

This index:

• Satisfies the full WHERE clause (affecteduser, object_type, object_id) as an equality prefix
• Includes timestamp as the trailing column, allowing the ORDER BY timestamp DESC to be served directly from the index without a filesort
• Covers the filter='filter' query path completely — the DB can do an index range scan in reverse order and stop after LIMIT rows

Added it to the occ command for missing indices instead of running as a migration.

[miaulalala]

/backport to stable33

[miaulalala]

/backport to stable32

[cypress]

ActivityRun #3431

Run Properties: Passed #3431 • 0ba49e5525: perf: add new index to serve a full WHERE clause

Project	Activity
Branch Review	perf/noid/add-where-index
Run status	Passed #3431
Run duration	02m 02s
Commit	0ba49e5525: perf: add new index to serve a full WHERE clause
Committer	Anna
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Test results
Failures	0
Flaky	0
Pending	1
Skipped	0
Passing	9
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[Altahrim]

Can we have an object_id with two different object_type?

[ChristophWurst]

Downtime None (maintenance mode already active; MySQL is online DDL)
Migration duration ~30–90 seconds for 1M rows

I'm slightly doubtful about this with oc_activity usually being one of the biggest table of a Nextcloud deployment. We have a mechanism for optional indices. Why not use that?
You can, of course, add the index to the migration that creates the table so it exists for new installations.

[miaulalala]

The query index specifically accelerates the per-object activity stream — the query that runs when a user opens the activity sidebar on a file or share.

Putting it in a repair step for the missing indices works as well, I don't have any preference.

[ChristophWurst]

The index will be missing for fresh installs unless you edit the migration that creates the table

[miaulalala]

/backport to stable32