fix: extend action c_u index to include created_unix for faster dashboard feeds

The c_u index on the action table was defined as (user_id, is_deleted)
without created_unix. The dashboard feed query filters by those two
columns and then orders by created_unix DESC, so the database had to
load and sort every matching row before it could return the first page
of 20 — causing 27+ second queries on large action tables.

Adds created_unix as the third column of the c_u index so the database
can seek to (user_id, is_deleted) and walk created_unix in reverse
order, stopping after 20 rows without a full sort.

Assisted-by: Claude:claude-sonnet-4-6

models/activities/action.go

@@ -166,7 +166,7 @@ func (a *Action) TableIndices() []*schemas.Index {
 	cudIndex.AddColumn("created_unix", "user_id", "is_deleted")
 
 	cuIndex := schemas.NewIndex("c_u", schemas.IndexType)
-	cuIndex.AddColumn("user_id", "is_deleted")
+	cuIndex.AddColumn("user_id", "is_deleted", "created_unix")
 
 	actUserUserIndex := schemas.NewIndex("au_c_u", schemas.IndexType)
 	actUserUserIndex.AddColumn("act_user_id", "created_unix", "user_id")

models/migrations/migrations.go

@@ -414,6 +414,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(334, "Add cancelling support to action runners", v1_27.AddCancellingSupportToActionRunner),
 		newMigration(335, "Add reusable workflow fields and action_run_attempt_job_id_index table for ActionRunJob", v1_27.AddReusableWorkflowFieldsToActionRunJob),
 		newMigration(336, "Add ActionRunJobSummary table", v1_27.AddActionRunJobSummaryTable),
+		newMigration(337, "Extend action c_u index to include created_unix for faster dashboard feed queries", v1_27.AddCreatedUnixToActionUserIsDeletedIndex),
 	}
 	return preparedMigrations
 }

models/migrations/v1_27/v337.go

@@ -0,0 +1,61 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_27
+
+import (
+	"gitea.dev/models/db"
+	"gitea.dev/modules/timeutil"
+
+	"xorm.io/xorm/schemas"
+)
+
+// actionWithUpdatedIndex is a minimal mirror of the action table used to apply
+// the updated c_u composite index (user_id, is_deleted, created_unix).
+// The previous index only covered (user_id, is_deleted), which forced the
+// database to sort all matching rows by created_unix before returning a page,
+// causing multi-second query times on large action tables.
+type actionWithUpdatedIndex struct {
+	ID          int64              `xorm:"pk autoincr"`
+	UserID      int64              `xorm:"INDEX"`
+	OpType      int
+	ActUserID   int64
+	RepoID      int64
+	CommentID   int64              `xorm:"INDEX"`
+	IsDeleted   bool               `xorm:"NOT NULL DEFAULT false"`
+	RefName     string
+	IsPrivate   bool               `xorm:"NOT NULL DEFAULT false"`
+	Content     string             `xorm:"TEXT"`
+	CreatedUnix timeutil.TimeStamp `xorm:"created"`
+}
+
+func (actionWithUpdatedIndex) TableName() string { return "action" }
+
+func (actionWithUpdatedIndex) TableIndices() []*schemas.Index {
+	repoIndex := schemas.NewIndex("r_u_d", schemas.IndexType)
+	repoIndex.AddColumn("repo_id", "user_id", "is_deleted")
+
+	actUserIndex := schemas.NewIndex("au_r_c_u_d", schemas.IndexType)
+	actUserIndex.AddColumn("act_user_id", "repo_id", "created_unix", "user_id", "is_deleted")
+
+	cudIndex := schemas.NewIndex("c_u_d", schemas.IndexType)
+	cudIndex.AddColumn("created_unix", "user_id", "is_deleted")
+
+	// Extended from (user_id, is_deleted) to include created_unix so that
+	// ORDER BY created_unix DESC on the dashboard query is satisfied by the
+	// index without a full sort of all matching rows.
+	cuIndex := schemas.NewIndex("c_u", schemas.IndexType)
+	cuIndex.AddColumn("user_id", "is_deleted", "created_unix")
+
+	actUserUserIndex := schemas.NewIndex("au_c_u", schemas.IndexType)
+	actUserUserIndex.AddColumn("act_user_id", "created_unix", "user_id")
+
+	return []*schemas.Index{actUserIndex, repoIndex, cudIndex, cuIndex, actUserUserIndex}
+}
+
+// AddCreatedUnixToActionUserIsDeletedIndex extends the c_u composite index on
+// the action table to include created_unix, enabling efficient ORDER BY on the
+// dashboard feed query without a full sort of all matching rows.
+func AddCreatedUnixToActionUserIsDeletedIndex(x db.EngineMigration) error {
+	return x.Sync(new(actionWithUpdatedIndex))
+}

models/migrations/v1_27/v337_test.go

@@ -0,0 +1,72 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_27
+
+import (
+	"context"
+	"testing"
+
+	"gitea.dev/models/migrations/migrationtest"
+	"gitea.dev/modules/timeutil"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"xorm.io/xorm/schemas"
+)
+
+type actionBeforeV337 struct {
+	ID          int64              `xorm:"pk autoincr"`
+	UserID      int64              `xorm:"INDEX"`
+	OpType      int
+	ActUserID   int64
+	RepoID      int64
+	CommentID   int64              `xorm:"INDEX"`
+	IsDeleted   bool               `xorm:"NOT NULL DEFAULT false"`
+	RefName     string
+	IsPrivate   bool               `xorm:"NOT NULL DEFAULT false"`
+	Content     string             `xorm:"TEXT"`
+	CreatedUnix timeutil.TimeStamp `xorm:"created"`
+}
+
+func (actionBeforeV337) TableName() string { return "action" }
+
+func (actionBeforeV337) TableIndices() []*schemas.Index {
+	repoIndex := schemas.NewIndex("r_u_d", schemas.IndexType)
+	repoIndex.AddColumn("repo_id", "user_id", "is_deleted")
+
+	actUserIndex := schemas.NewIndex("au_r_c_u_d", schemas.IndexType)
+	actUserIndex.AddColumn("act_user_id", "repo_id", "created_unix", "user_id", "is_deleted")
+
+	cudIndex := schemas.NewIndex("c_u_d", schemas.IndexType)
+	cudIndex.AddColumn("created_unix", "user_id", "is_deleted")
+
+	// old 2-column index, before the migration
+	cuIndex := schemas.NewIndex("c_u", schemas.IndexType)
+	cuIndex.AddColumn("user_id", "is_deleted")
+
+	actUserUserIndex := schemas.NewIndex("au_c_u", schemas.IndexType)
+	actUserUserIndex.AddColumn("act_user_id", "created_unix", "user_id")
+
+	return []*schemas.Index{actUserIndex, repoIndex, cudIndex, cuIndex, actUserUserIndex}
+}
+
+func Test_AddCreatedUnixToActionUserIsDeletedIndex(t *testing.T) {
+	x, deferable := migrationtest.PrepareTestEnv(t, 0, new(actionBeforeV337))
+	defer deferable()
+	if x == nil || t.Failed() {
+		return
+	}
+
+	indexes, err := x.Dialect().GetIndexes(x.DB(), context.Background(), "action")
+	require.NoError(t, err)
+	assert.True(t, hasIndexWithColumns(indexes, []string{"user_id", "is_deleted"}, false), "old c_u index should exist before migration")
+	assert.False(t, hasIndexWithColumns(indexes, []string{"user_id", "is_deleted", "created_unix"}, false), "new c_u index should not exist before migration")
+
+	require.NoError(t, AddCreatedUnixToActionUserIsDeletedIndex(x))
+
+	indexes, err = x.Dialect().GetIndexes(x.DB(), context.Background(), "action")
+	require.NoError(t, err)
+	assert.False(t, hasIndexWithColumns(indexes, []string{"user_id", "is_deleted"}, false), "old 2-column c_u index should be gone after migration")
+	assert.True(t, hasIndexWithColumns(indexes, []string{"user_id", "is_deleted", "created_unix"}, false), "new 3-column c_u index must exist after migration")
+}