fix: realign indexes on the 'action' table (#10040)

Fixes #9963.  This realigns all the indexes on the `action` table to best match their intended usages.

New:
- `IDX_action_created_unix (created_unix)`
    - Intended for usage in `DeleteOldActions`.
- `IDX_action_repo_id_created_unix (repo_id, created_unix)`
    - Intended for usage when fetching action feeds for a repo and a team, with the same logic as that described below in `IDX_action_user_id_created_unix`.
- `IDX_action_repo_id_op_type (repo_id, op_type)`
    - Intended for `DeleteIssueActions` when it searches for CreateIssue & CreatePullRequest actions for cleanup.  Could be optimized further with a denormalization of the issue identifier into a field, but there's no current evidence that this is required.

Replaced:
- `IDX_action_c_u (created_unix, user_id)`
    - Replaced with `IDX_action_user_id_created_unix (user_id, created_unix)`.  When action feeds are created w/ `ORDER BY created_unix DESC LIMIT 20`, an index beginning with `created_unix` will have to index scan until it can satisfy 20 records; the `user_id` portion of the index is effectively useless until two records appear at the same time.  By inverting the order, the database will be able to identify the records created by a user and then pop the most recent 20 from the index order.
    - At the scale of database I have access to, the performance difference is unmeasurable.  This change is supported by theoretical grounds and the findings of #9963, but no experimental evidence.

Removed:
- `IDX_action_user_id (user_id)`
    - Redundant with the new `IDX_action_user_id_created_unix`.
- `IDX_action_r_u (repo_id, user_id)`
    - No clear consumer for this index.

Retained with no modification:
- `IDX_action_comment_id (comment_id)`
    - Used in `DeleteIssueActions`.
- `IDX_action_au_r_c_u (act_user_id, repo_id, created_unix, user_id)`
    - Heat map generation.

## Checklist

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### Tests

- I added test coverage for Go changes...
  - [ ] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [ ] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] I do not want this change to show in the release notes.
- [x] I want the title to show in the release notes with a link to this pull request.
- [ ] I want the content of the `release-notes/<pull request number>.md` to be be used for the release notes instead of the title.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10040
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>

models/activities/action.go

@@ -145,37 +145,49 @@ func (at ActionType) InActions(actions ...string) bool {
 // used in template render.
 type Action struct {
 	ID          int64 `xorm:"pk autoincr"`
-	UserID      int64 `xorm:"INDEX"` // Receiver user id.
+	UserID      int64 // Receiver user id.
 	OpType      ActionType
 	ActUserID   int64            // Action user id.
 	ActUser     *user_model.User `xorm:"-"`
 	RepoID      int64
 	Repo        *repo_model.Repository `xorm:"-"`
-	CommentID   int64                  `xorm:"INDEX"`
+	CommentID   int64                  `xorm:"INDEX"` // indexed to support `DeleteIssueActions`
 	Comment     *issues_model.Comment  `xorm:"-"`
 	Issue       *issues_model.Issue    `xorm:"-"` // get the issue id from content
 	RefName     string
 	IsPrivate   bool               `xorm:"NOT NULL DEFAULT false"`
 	Content     string             `xorm:"TEXT"`
-	CreatedUnix timeutil.TimeStamp `xorm:"created"`
+	CreatedUnix timeutil.TimeStamp `xorm:"created INDEX"` // indexed to support `DeleteOldActions`
 }
 
 func init() {
 	db.RegisterModel(new(Action))
 }
 
-// TableIndices implements xorm's TableIndices interface
+// TableIndices implements xorm's TableIndices interface.  It is used here to ensure indexes with specified column order
+// are created, which can't be created through xorm tags on the struct.
 func (a *Action) TableIndices() []*schemas.Index {
-	repoIndex := schemas.NewIndex("r_u", schemas.IndexType)
-	repoIndex.AddColumn("repo_id", "user_id")
-
+	// Index to support getUserHeatmapData, which searches for data that is visible-to (user_id) and performed-by
+	// (act_user_id) a user, but only includes visible repos (repo_id).
 	actUserIndex := schemas.NewIndex("au_r_c_u", schemas.IndexType)
 	actUserIndex.AddColumn("act_user_id", "repo_id", "created_unix", "user_id")
 
-	cudIndex := schemas.NewIndex("c_u", schemas.IndexType)
-	cudIndex.AddColumn("created_unix", "user_id")
+	// GetFeeds is a common access point to Action and requires that all action feeds be queried based upon one of
+	// user_id (opts.RequestedUser), repo_id (opts.RequestedTeam... kinda), and/or repo_id (opts.RequestedRepo), and
+	// then the results are ordered by created_unix and paginated.  The most efficient indexes to support those queries
+	// are:
+	requestedUser := schemas.NewIndex("user_id_created_unix", schemas.IndexType)
+	requestedUser.AddColumn("user_id", "created_unix")
+	requestedRepo := schemas.NewIndex("repo_id_created_unix", schemas.IndexType)
+	requestedRepo.AddColumn("repo_id", "created_unix")
 
-	indices := []*schemas.Index{actUserIndex, repoIndex, cudIndex}
+	// To support `DeleteIssueActions` search for createissue / createpullrequest actions; this isn't a great search
+	// because `DeleteIssueActions` searches by `content` as well, but it should be sufficient performance-wise for
+	// infrequent deleting of issues.
+	repoOpType := schemas.NewIndex("repo_id_op_type", schemas.IndexType)
+	repoOpType.AddColumn("repo_id", "op_type")
+
+	indices := []*schemas.Index{actUserIndex, requestedUser, requestedRepo, repoOpType}
 
 	return indices
 }