[GITEA] Avoid WHERE IN for comment migration query

- Rewrite `UpdateCommentsMigrationsByType` to not use `WHERE IN` as
that's a performance diaster for MariaDB, it now use batching to query
the the relevant comment IDs via JOINs (which is not possible in a
UPDATE query for SQLite) and then update them in a seperate query.
- Add unit test.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1856

models/issues/comment.go

@@ -1177,23 +1177,37 @@ func DeleteComment(ctx context.Context, comment *Comment) error {
 
 // UpdateCommentsMigrationsByType updates comments' migrations information via given git service type and original id and poster id
 func UpdateCommentsMigrationsByType(ctx context.Context, tp structs.GitServiceType, originalAuthorID string, posterID int64) error {
-	_, err := db.GetEngine(ctx).Table("comment").
-		Where(builder.In("issue_id",
-			builder.Select("issue.id").
-				From("issue").
-				InnerJoin("repository", "issue.repo_id = repository.id").
-				Where(builder.Eq{
-					"repository.original_service_type": tp,
-				}),
-		)).
-		And("comment.original_author_id = ?", originalAuthorID).
-		Update(map[string]any{
+	const batchSize = 50
+	for {
+		commentIDs := make([]int64, 0, batchSize)
+		if err := db.GetEngine(ctx).
+			Table("comment").
+			Select("`comment`.id").
+			Join("INNER", "issue", "`comment`.issue_id = `issue`.id").
+			Join("INNER", "repository", "`repository`.id = `issue`.repo_id").
+			Where("`repository`.original_service_type = ? AND `comment`.original_author_id = ?", tp, originalAuthorID).
+			Limit(batchSize, 0).
+			Find(&commentIDs); err != nil {
+			return err
+		}
+
+		for _, commentID := range commentIDs {
+			if _, err := db.GetEngine(ctx).Table(&Comment{}).ID(commentID).Update(map[string]any{
 				"poster_id":          posterID,
 				"original_author":    "",
 				"original_author_id": 0,
-		})
+			}); err != nil {
 				return err
 			}
+		}
+
+		if len(commentIDs) < batchSize {
+			break
+		}
+	}
+
+	return nil
+}
 
 // CreateAutoMergeComment is a internal function, only use it for CommentTypePRScheduledToAutoMerge and CommentTypePRUnScheduledToAutoMerge CommentTypes
 func CreateAutoMergeComment(ctx context.Context, typ CommentType, pr *PullRequest, doer *user_model.User) (comment *Comment, err error) {

models/issues/comment_test.go

@@ -12,6 +12,7 @@ import (
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/structs"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -97,3 +98,29 @@ func TestMigrate_InsertIssueComments(t *testing.T) {
 
 	unittest.CheckConsistencyFor(t, &issues_model.Issue{})
 }
+
+func TestUpdateCommentsMigrationsByType(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	issue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 1})
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: issue.RepoID})
+	comment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: 1, IssueID: issue.ID})
+
+	// Set repository to migrated from Gitea.
+	repo.OriginalServiceType = structs.GiteaService
+	repo_model.UpdateRepositoryCols(db.DefaultContext, repo, "original_service_type")
+
+	// Set comment to have an original author.
+	comment.OriginalAuthor = "Example User"
+	comment.OriginalAuthorID = 1
+	comment.PosterID = 0
+	_, err := db.GetEngine(db.DefaultContext).ID(comment.ID).Cols("original_author", "original_author_id", "poster_id").Update(comment)
+	assert.NoError(t, err)
+
+	assert.NoError(t, issues_model.UpdateCommentsMigrationsByType(db.DefaultContext, structs.GiteaService, "1", 513))
+
+	comment = unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: 1, IssueID: issue.ID})
+	assert.Empty(t, comment.OriginalAuthor)
+	assert.Empty(t, comment.OriginalAuthorID)
+	assert.EqualValues(t, 513, comment.PosterID)
+}