Delete jobs without loading objects first

The commit is intended to speed up the cleanup_jobs command in awx. Old
methods takes 7+ hours to delete 1 million old jobs. New method takes
around 6 minutes.

Leverages a sub-classed Collector, called AWXCollector, that does not
load in objects before deleting them. Instead querysets, which are
lazily evaluated, are used in places where Collector normally keeps a
list of objects.

Finally, a couple of tests to ensure parity between old Collector and
AWXCollector. That is, any object that is updated/removed from the
database using Collector should be have identical operations using
AWXCollector.

tower issue 1103

awx/main/management/commands/cleanup_jobs.py

@@ -21,6 +21,8 @@
     disable_computed_fields
 )
 
+from awx.main.management.commands.deletion import AWXCollector, pre_delete
+
 
 class Command(BaseCommand):
     '''
@@ -57,27 +59,37 @@ def add_arguments(self, parser):
                             action='store_true', dest='only_workflow_jobs',
                             help='Remove workflow jobs')
 
+
     def cleanup_jobs(self):
-        #jobs_qs = Job.objects.exclude(status__in=('pending', 'running'))
-        #jobs_qs = jobs_qs.filter(created__lte=self.cutoff)
         skipped, deleted = 0, 0
-        jobs = Job.objects.filter(created__lt=self.cutoff)
-        for job in jobs.iterator():
-            job_display = '"%s" (%d host summaries, %d events)' % \
-                          (str(job),
-                           job.job_host_summaries.count(), job.job_events.count())
-            if job.status in ('pending', 'waiting', 'running'):
-                action_text = 'would skip' if self.dry_run else 'skipping'
-                self.logger.debug('%s %s job %s', action_text, job.status, job_display)
-                skipped += 1
+
+        batch_size = 1000000
+
+        while True:
+            # get queryset for available jobs to remove
+            qs = Job.objects.filter(created__lt=self.cutoff).exclude(status__in=['pending', 'waiting', 'running'])
+            # get pk list for the first N (batch_size) objects
+            pk_list = qs[0:batch_size].values_list('pk')
+            # You cannot delete queries with sql LIMIT set, so we must
+            # create a new query from this pk_list
+            qs_batch = Job.objects.filter(pk__in=pk_list)
+            just_deleted = 0
+            if not self.dry_run:
+                del_query = pre_delete(qs_batch)
+                collector = AWXCollector(del_query.db)
+                collector.collect(del_query)
+                _, models_deleted = collector.delete()
+                if models_deleted:
+                    just_deleted = models_deleted['main.Job']
+                deleted += just_deleted
             else:
-                action_text = 'would delete' if self.dry_run else 'deleting'
-                self.logger.info('%s %s', action_text, job_display)
-                if not self.dry_run:
-                    job.delete()
-                deleted += 1
+                just_deleted = 0 # break from loop, this is dry run
+                deleted = qs.count()
+
+            if just_deleted == 0:
+                break
 
-        skipped += Job.objects.filter(created__gte=self.cutoff).count()
+        skipped += (Job.objects.filter(created__gte=self.cutoff) | Job.objects.filter(status__in=['pending', 'waiting', 'running'])).count()
         return skipped, deleted
 
     def cleanup_ad_hoc_commands(self):

awx/main/management/commands/deletion.py

@@ -0,0 +1,177 @@
+from django.contrib.contenttypes.models import ContentType
+from django.db.models.deletion import (
+    DO_NOTHING, Collector, get_candidate_relations_to_delete,
+)
+from collections import Counter, OrderedDict
+from django.db import transaction
+from django.db.models import sql
+
+
+def bulk_related_objects(field, objs, using):
+    # This overrides the method in django.contrib.contenttypes.fields.py
+    """
+    Return all objects related to ``objs`` via this ``GenericRelation``.
+    """
+    return field.remote_field.model._base_manager.db_manager(using).filter(**{
+        "%s__pk" % field.content_type_field_name: ContentType.objects.db_manager(using).get_for_model(
+            field.model, for_concrete_model=field.for_concrete_model).pk,
+        "%s__in" % field.object_id_field_name: list(objs.values_list('pk', flat=True))
+    })
+
+
+def pre_delete(qs):
+    # taken from .delete method in django.db.models.query.py
+    assert qs.query.can_filter(), \
+        "Cannot use 'limit' or 'offset' with delete."
+
+    if qs._fields is not None:
+        raise TypeError("Cannot call delete() after .values() or .values_list()")
+
+    del_query = qs._chain()
+
+    # The delete is actually 2 queries - one to find related objects,
+    # and one to delete. Make sure that the discovery of related
+    # objects is performed on the same database as the deletion.
+    del_query._for_write = True
+
+    # Disable non-supported fields.
+    del_query.query.select_for_update = False
+    del_query.query.select_related = False
+    del_query.query.clear_ordering(force_empty=True)
+    return del_query
+
+
+class AWXCollector(Collector):
+
+    def add(self, objs, source=None, nullable=False, reverse_dependency=False):
+        """
+        Add 'objs' to the collection of objects to be deleted.  If the call is
+        the result of a cascade, 'source' should be the model that caused it,
+        and 'nullable' should be set to True if the relation can be null.
+
+        Return a list of all objects that were not already collected.
+        """
+        if not objs.exists():
+            return objs
+        model = objs.model
+        self.data.setdefault(model, [])
+        self.data[model].append(objs)
+        # Nullable relationships can be ignored -- they are nulled out before
+        # deleting, and therefore do not affect the order in which objects have
+        # to be deleted.
+        if source is not None and not nullable:
+            if reverse_dependency:
+                source, model = model, source
+            self.dependencies.setdefault(
+                source._meta.concrete_model, set()).add(model._meta.concrete_model)
+        return objs
+
+    def add_field_update(self, field, value, objs):
+        """
+        Schedule a field update. 'objs' must be a homogeneous iterable
+        collection of model instances (e.g. a QuerySet).
+        """
+        if not objs.exists():
+            return
+        model = objs.model
+        self.field_updates.setdefault(model, {})
+        self.field_updates[model].setdefault((field, value), [])
+        self.field_updates[model][(field, value)].append(objs)
+
+    def collect(self, objs, source=None, nullable=False, collect_related=True,
+                source_attr=None, reverse_dependency=False, keep_parents=False):
+        """
+        Add 'objs' to the collection of objects to be deleted as well as all
+        parent instances.  'objs' must be a homogeneous iterable collection of
+        model instances (e.g. a QuerySet).  If 'collect_related' is True,
+        related objects will be handled by their respective on_delete handler.
+
+        If the call is the result of a cascade, 'source' should be the model
+        that caused it and 'nullable' should be set to True, if the relation
+        can be null.
+
+        If 'reverse_dependency' is True, 'source' will be deleted before the
+        current model, rather than after. (Needed for cascading to parent
+        models, the one case in which the cascade follows the forwards
+        direction of an FK rather than the reverse direction.)
+
+        If 'keep_parents' is True, data of parent model's will be not deleted.
+        """
+
+        if hasattr(objs, 'polymorphic_disabled'):
+            objs.polymorphic_disabled = True
+
+        if self.can_fast_delete(objs):
+            self.fast_deletes.append(objs)
+            return
+        new_objs = self.add(objs, source, nullable,
+                            reverse_dependency=reverse_dependency)
+        if not new_objs.exists():
+            return
+
+        model = new_objs.model
+
+        if not keep_parents:
+            # Recursively collect concrete model's parent models, but not their
+            # related objects. These will be found by meta.get_fields()
+            concrete_model = model._meta.concrete_model
+            for ptr in concrete_model._meta.parents.keys():
+                if ptr:
+                    parent_objs = ptr.objects.filter(pk__in = new_objs.values_list('pk', flat=True))
+                    self.collect(parent_objs, source=model,
+                                 collect_related=False,
+                                 reverse_dependency=True)
+        if collect_related:
+            parents = model._meta.parents
+            for related in get_candidate_relations_to_delete(model._meta):
+                # Preserve parent reverse relationships if keep_parents=True.
+                if keep_parents and related.model in parents:
+                    continue
+                field = related.field
+                if field.remote_field.on_delete == DO_NOTHING:
+                    continue
+                related_qs = self.related_objects(related, new_objs)
+                if self.can_fast_delete(related_qs, from_field=field):
+                    self.fast_deletes.append(related_qs)
+                elif related_qs:
+                    field.remote_field.on_delete(self, field, related_qs, self.using)
+            for field in model._meta.private_fields:
+                if hasattr(field, 'bulk_related_objects'):
+                    # It's something like generic foreign key.
+                    sub_objs = bulk_related_objects(field, new_objs, self.using)
+                    self.collect(sub_objs, source=model, nullable=True)
+
+    def delete(self):
+        self.sort()
+
+        # collect pk_list before deletion (once things start to delete
+        # queries might not be able to retreive pk list)
+        del_dict = OrderedDict()
+        for model, instances in self.data.items():
+            del_dict.setdefault(model, [])
+            for inst in instances:
+                del_dict[model] += list(inst.values_list('pk', flat=True))
+
+        deleted_counter = Counter()
+
+        with transaction.atomic(using=self.using, savepoint=False):
+
+            # update fields
+            for model, instances_for_fieldvalues in self.field_updates.items():
+                for (field, value), instances in instances_for_fieldvalues.items():
+                    for inst in instances:
+                        query = sql.UpdateQuery(model)
+                        query.update_batch(inst.values_list('pk', flat=True),
+                                           {field.name: value}, self.using)
+            # fast deletes
+            for qs in self.fast_deletes:
+                count = qs._raw_delete(using=self.using)
+                deleted_counter[qs.model._meta.label] += count
+
+            # delete instances
+            for model, pk_list in del_dict.items():
+                query = sql.DeleteQuery(model)
+                count = query.delete_batch(pk_list, self.using)
+                deleted_counter[model._meta.label] += count
+
+            return sum(deleted_counter.values()), dict(deleted_counter)