unit: Add md5 index on source/target/context fields

This improves exact strings lookups like done in automatic translation
or consistency checks.

Issue #9118
Issue #1994

weblate/trans/autotranslate.py

@@ -8,6 +8,7 @@
 from django.conf import settings
 from django.core.exceptions import PermissionDenied
 from django.db import transaction
+from django.db.models.functions import MD5
 
 from weblate.machinery.models import MACHINERY
 from weblate.trans.models import Change, Component, Suggestion, Unit
@@ -119,7 +120,9 @@ def process_others(self, source: Optional[int]):
         translations = {
             source: split_plural(target)
             for source, state, target in sources.filter(
-                source__in=self.get_units().values("source")
+                source__md5__in=self.get_units()
+                .annotate(source__md5=MD5("source"))
+                .values("source__md5")
             ).values_list("source", "state", "target")
         }
 

weblate/trans/migrations/0169_unit_trans_unit_source_md5_index_and_more.py

@@ -0,0 +1,38 @@
+# Copyright © Michal Čihař <michal@weblate.org>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Generated by Django 4.2.1 on 2023-05-18 11:58
+
+import django.db.models.functions.text
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("trans", "0168_unit_last_updated_unit_target_hash"),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name="unit",
+            index=models.Index(
+                django.db.models.functions.text.MD5("source"),
+                name="trans_unit_source_md5_index",
+            ),
+        ),
+        migrations.AddIndex(
+            model_name="unit",
+            index=models.Index(
+                django.db.models.functions.text.MD5("target"),
+                name="trans_unit_target_md5_index",
+            ),
+        ),
+        migrations.AddIndex(
+            model_name="unit",
+            index=models.Index(
+                django.db.models.functions.text.MD5("context"),
+                name="trans_unit_context_md5_index",
+            ),
+        ),
+    ]

weblate/trans/models/unit.py

@@ -9,7 +9,8 @@
 from django.core.cache import cache
 from django.db import Error as DjangoDatabaseError
 from django.db import models, transaction
-from django.db.models import Count, Max, Q
+from django.db.models import Count, Max, Q, Value
+from django.db.models.functions import MD5
 from django.utils import timezone
 from django.utils.functional import cached_property
 from django.utils.translation import gettext, gettext_lazy, gettext_noop
@@ -139,8 +140,8 @@ def same(self, unit, exclude=True):
         translation = unit.translation
         component = translation.component
         result = self.filter(
-            source=unit.source,
-            context=unit.context,
+            source__md5=MD5(Value(unit.source)),
+            context__md5=MD5(Value(unit.context)),
             translation__component__project_id=component.project_id,
             translation__language_id=translation.language_id,
             translation__component__source_language_id=component.source_language_id,
@@ -340,6 +341,11 @@ class Meta:
         unique_together = [("translation", "id_hash")]
         verbose_name = "string"
         verbose_name_plural = "strings"
+        indexes = [
+            models.Index(MD5("source"), name="trans_unit_source_md5_index"),
+            models.Index(MD5("target"), name="trans_unit_target_md5_index"),
+            models.Index(MD5("context"), name="trans_unit_context_md5_index"),
+        ]
 
     def __str__(self):
         if self.translation.is_template:

weblate/utils/apps.py

@@ -5,6 +5,7 @@
 from django.apps import AppConfig
 from django.core.checks import register
 from django.db.models import CharField, TextField
+from django.db.models.functions import MD5
 from django.db.models.lookups import Regex
 
 from weblate.utils.checks import (
@@ -55,17 +56,19 @@ def ready(self):
         init_error_collection()
 
         if using_postgresql():
-            lookups = (
+            lookups = [
                 (PostgreSQLSearchLookup,),
                 (PostgreSQLSubstringLookup,),
                 (PostgreSQLRegexLookup, "trgm_regex"),
-            )
+            ]
         else:
-            lookups = (
+            lookups = [
                 (MySQLSearchLookup,),
                 (MySQLSearchLookup, "substring"),
                 (Regex, "trgm_regex"),
-            )
+            ]
+
+        lookups.append((MD5,))
 
         for lookup in lookups:
             CharField.register_lookup(*lookup)