fix: DEV-2667: Replace inner_id index with multicolumn (#2542)

Author: triklozoid

label_studio/tasks/migrations/0023_auto_20220620_1007.py

@@ -0,0 +1,22 @@
+# Generated by Django 3.1.14 on 2022-06-20 10:07
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tasks', '0022_merge_20220517_1128'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='task',
+            name='inner_id',
+            field=models.BigIntegerField(default=0, help_text='Internal task ID in the project, starts with 1', null=True, verbose_name='inner id'),
+        ),
+        migrations.AddIndex(
+            model_name='task',
+            index=models.Index(fields=['project', 'inner_id'], name='task_project_499b59_idx'),
+        ),
+    ]

label_studio/tasks/models.py

@@ -66,7 +66,7 @@ class Task(TaskMixin, models.Model):
         'data_import.FileUpload', on_delete=models.SET_NULL, null=True, blank=True, related_name='tasks',
         help_text='Uploaded file used as data source for this task'
     )
-    inner_id = models.BigIntegerField(_('inner id'), default=0, db_index=True, null=True,
+    inner_id = models.BigIntegerField(_('inner id'), default=0, null=True,
                                       help_text='Internal task ID in the project, starts with 1')
     updates = ['is_labeled']
     total_annotations = models.IntegerField(_('total_annotations'), default=0, db_index=True,
@@ -83,6 +83,7 @@ class Meta:
         ordering = ['-updated_at']
         indexes = [
             models.Index(fields=['project', 'is_labeled']),
+            models.Index(fields=['project', 'inner_id']),
             models.Index(fields=['id', 'project']),
             models.Index(fields=['id', 'overlap']),
             models.Index(fields=['overlap']),