models: Add new UserMessage flag active_mobile_push_notification.

This flag is used to track which user/message pairs correspond to an
active mobile push notification, that should potentially be cleared
when the user reads the message.

This flag should never appear on a message that is also marked as
read; eventually we may want a cron job to check for that condition.

We include a partial index on UserMessage for this flag.

docs/production/expensive-migrations.md

@@ -24,8 +24,12 @@ can run them manually before starting the upgrade:
         ON zerver_usermessage (user_profile_id, message_id)
         WHERE (flags & 2048) != 0;
 
-(This first migration, `zerver_usermessage_is_private_message_id`, is
+        CREATE INDEX CONCURRENTLY
-the only one new in Zulip 1.9).
+        zerver_usermessage_active_mobile_push_notification_id
+        ON zerver_usermessage (user_profile_id, message_id)
+        WHERE (flags & 4096) != 0;
+
+(These first migrations are the only new ones in Zulip 1.9).
 
         CREATE INDEX CONCURRENTLY
         zerver_usermessage_mentioned_message_id

scripts/lib/upgrade-zulip-stage-2

@@ -99,6 +99,7 @@ usermessage_index_migrations = [
     "[ ] 0098_index_has_alert_word_user_messages",
     "[ ] 0099_index_wildcard_mentioned_user_messages",
     "[ ] 0177_user_message_add_and_index_is_private_flag",
+    "[ ] 0180_usermessage_add_active_mobile_push_notification",
 ]
 # Our next optimization is to check whether any migrations are needed
 # before we start the critical section of the restart.  This saves

zerver/management/commands/create_large_indexes.py

@@ -96,6 +96,14 @@ def create_indexes() -> None:
         where_clause='WHERE (flags & 2048) != 0',
     )
 
+    # copied from 0180
+    create_index_if_not_exist(
+        index_name='zerver_usermessage_active_mobile_push_notification_id',
+        table_name='zerver_usermessage',
+        column_string='user_profile_id, message_id',
+        where_clause='WHERE (flags & 4096) != 0',
+    )
+
 class Command(ZulipBaseCommand):
     help = """Create concurrent indexes for large tables."""
 

zerver/migrations/0180_usermessage_add_active_mobile_push_notification.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.14 on 2018-08-01 23:05
+from __future__ import unicode_literals
+
+import bitfield.models
+from django.db import migrations
+from zerver.lib.migrate import create_index_if_not_exist  # nolint
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zerver', '0179_rename_to_digest_emails_enabled'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='archivedusermessage',
+            name='flags',
+            field=bitfield.models.BitField(['read', 'starred', 'collapsed', 'mentioned', 'wildcard_mentioned', 'summarize_in_home', 'summarize_in_stream', 'force_expand', 'force_collapse', 'has_alert_word', 'historical', 'is_private', 'active_mobile_push_notification'], default=0),
+        ),
+        migrations.AlterField(
+            model_name='usermessage',
+            name='flags',
+            field=bitfield.models.BitField(['read', 'starred', 'collapsed', 'mentioned', 'wildcard_mentioned', 'summarize_in_home', 'summarize_in_stream', 'force_expand', 'force_collapse', 'has_alert_word', 'historical', 'is_private', 'active_mobile_push_notification'], default=0),
+        ),
+        migrations.RunSQL(
+            create_index_if_not_exist(
+                index_name='zerver_usermessage_active_mobile_push_notification_id',
+                table_name='zerver_usermessage',
+                column_string='user_profile_id, message_id',
+                where_clause='WHERE (flags & 4096) != 0',
+            ),
+            reverse_sql='DROP INDEX zerver_usermessage_active_mobile_push_notification_id;'
+        ),
+    ]

zerver/models.py

@@ -1524,7 +1524,7 @@ class AbstractUserMessage(models.Model):
     user_profile = models.ForeignKey(UserProfile, on_delete=CASCADE)  # type: UserProfile
     ALL_FLAGS = ['read', 'starred', 'collapsed', 'mentioned', 'wildcard_mentioned',
                  'summarize_in_home', 'summarize_in_stream', 'force_expand', 'force_collapse',
-                 'has_alert_word', "historical", "is_private"]
+                 'has_alert_word', "historical", "is_private", "active_mobile_push_notification"]
     flags = BitField(flags=ALL_FLAGS, default=0)  # type: BitHandler
 
     class Meta: