Merge lp:~allenap/maas/power-poll-fewer--bug-1389007--1.8 into lp:maas/1.8

[Gavin Panella]

Backport r4076 from lp:maas: Query node power states in smaller batches.

[Gavin Panella (allenap)]

Selfie (backport).

review: Approve

=== modified file 'HACKING.txt'
--- HACKING.txt	2015-05-20 23:53:24 +0000
+++ HACKING.txt	2015-07-15 12:15:32 +0000
@@ -449,13 +449,19 @@
 
 .. _schemamigration: http://south.aeracode.org/docs/commands.html#schemamigration
 
-Once you've changed the code, run::
+Once you've changed the code, ensure the database is running and
+contains the starting schema::
+
+    $ make services/database/@start
+    $ make syncdb
+
+then generate the migration script with::
 
     $ ./bin/maas-region-admin schemamigration maasserver --auto description_of_the_change
 
 This will generate a migration module named
-``src/maasserver/migrations/<auto_number>_description_of_the_change.py``. Don't
-forget to add that file to the project with::
+``src/maasserver/migrations/<auto_number>_description_of_the_change.py``.
+Don't forget to add that file to the project with::
 
     $ bzr add src/maasserver/migrations/<auto_number>_description_of_the_change.py
 
 
=== added file 'src/maasserver/migrations/0139_power_parameters_and_state_updated_field.py'
--- src/maasserver/migrations/0139_power_parameters_and_state_updated_field.py	1970-01-01 00:00:00 +0000
+++ src/maasserver/migrations/0139_power_parameters_and_state_updated_field.py	2015-07-15 12:15:32 +0000
@@ -0,0 +1,453 @@
+# -*- coding: utf-8 -*-
+from django.db import models
+from south.db import db
+from south.utils import datetime_utils as datetime
+from south.v2 import SchemaMigration
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        # Adding field 'Node.power_state_updated'
+        db.add_column(u'maasserver_node', 'power_state_updated',
+                      self.gf('django.db.models.fields.DateTimeField')(default=None, null=True),
+                      keep_default=False)
+
+
+        # Changing field 'Node.power_parameters'
+        db.alter_column(u'maasserver_node', 'power_parameters', self.gf('maasserver.fields.JSONObjectField')(max_length=32768))
+
+    def backwards(self, orm):
+        # Deleting field 'Node.power_state_updated'
+        db.delete_column(u'maasserver_node', 'power_state_updated')
+
+
+        # Changing field 'Node.power_parameters'
+        db.alter_column(u'maasserver_node', 'power_parameters', self.gf('maasserver.fields.JSONObjectField')())
+
+    models = {
+        u'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        u'auth.permission': {
+            'Meta': {'ordering': "(u'content_type__app_label', u'content_type__model', u'codename')", 'unique_together': "((u'content_type', u'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        u'auth.user': {
+            'Meta': {'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'unique': 'True', 'max_length': '75', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'symmetrical': 'False', 'related_name': "u'user_set'", 'blank': 'True', 'to': u"orm['auth.Group']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '128'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'symmetrical': 'False', 'related_name': "u'user_set'", 'blank': 'True', 'to': u"orm['auth.Permission']"}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '30'})
+        },
+        u'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        u'maasserver.blockdevice': {
+            'Meta': {'ordering': "[u'id']", 'unique_together': "((u'node', u'path'),)", 'object_name': 'BlockDevice'},
+            'block_size': ('django.db.models.fields.IntegerField', [], {}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'id_path': ('django.db.models.fields.FilePathField', [], {'max_length': '100', 'null': 'True', 'blank': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'node': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.Node']"}),
+            'path': ('django.db.models.fields.FilePathField', [], {'max_length': '100'}),
+            'size': ('django.db.models.fields.BigIntegerField', [], {}),
+            'tags': ('djorm_pgarray.fields.ArrayField', [], {'default': '[]', 'dbtype': "u'text'", 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.bootresource': {
+            'Meta': {'unique_together': "((u'name', u'architecture'),)", 'object_name': 'BootResource'},
+            'architecture': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'extra': ('maasserver.fields.JSONObjectField', [], {'default': "u''", 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'rtype': ('django.db.models.fields.IntegerField', [], {'max_length': '10'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.bootresourcefile': {
+            'Meta': {'unique_together': "((u'resource_set', u'filetype'),)", 'object_name': 'BootResourceFile'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'extra': ('maasserver.fields.JSONObjectField', [], {'default': "u''", 'blank': 'True'}),
+            'filename': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'filetype': ('django.db.models.fields.CharField', [], {'default': "u'root-tgz'", 'max_length': '20'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'largefile': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.LargeFile']"}),
+            'resource_set': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "u'files'", 'to': u"orm['maasserver.BootResourceSet']"}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.bootresourceset': {
+            'Meta': {'unique_together': "((u'resource', u'version'),)", 'object_name': 'BootResourceSet'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'label': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'resource': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "u'sets'", 'to': u"orm['maasserver.BootResource']"}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'version': ('django.db.models.fields.CharField', [], {'max_length': '255'})
+        },
+        u'maasserver.bootsource': {
+            'Meta': {'object_name': 'BootSource'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'keyring_data': ('maasserver.fields.EditableBinaryField', [], {'blank': 'True'}),
+            'keyring_filename': ('django.db.models.fields.FilePathField', [], {'max_length': '100', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'url': ('django.db.models.fields.URLField', [], {'unique': 'True', 'max_length': '200'})
+        },
+        u'maasserver.bootsourcecache': {
+            'Meta': {'object_name': 'BootSourceCache'},
+            'arch': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            'boot_source': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.BootSource']"}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'label': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            'os': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            'release': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            'subarch': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.bootsourceselection': {
+            'Meta': {'unique_together': "((u'boot_source', u'os', u'release'),)", 'object_name': 'BootSourceSelection'},
+            'arches': ('djorm_pgarray.fields.ArrayField', [], {'default': 'None', 'dbtype': "u'text'", 'null': 'True', 'blank': 'True'}),
+            'boot_source': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.BootSource']"}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'labels': ('djorm_pgarray.fields.ArrayField', [], {'default': 'None', 'dbtype': "u'text'", 'null': 'True', 'blank': 'True'}),
+            'os': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '20', 'blank': 'True'}),
+            'release': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '20', 'blank': 'True'}),
+            'subarches': ('djorm_pgarray.fields.ArrayField', [], {'default': 'None', 'dbtype': "u'text'", 'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.candidatename': {
+            'Meta': {'unique_together': "((u'name', u'position'),)", 'object_name': 'CandidateName'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.SlugField', [], {'max_length': '50'}),
+            'position': ('django.db.models.fields.IntegerField', [], {})
+        },
+        u'maasserver.componenterror': {
+            'Meta': {'object_name': 'ComponentError'},
+            'component': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '40'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'error': ('django.db.models.fields.CharField', [], {'max_length': '1000'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.config': {
+            'Meta': {'object_name': 'Config'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '255'}),
+            'value': ('maasserver.fields.JSONObjectField', [], {'null': 'True'})
+        },
+        u'maasserver.dhcplease': {
+            'Meta': {'object_name': 'DHCPLease'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'ip': ('maasserver.fields.MAASIPAddressField', [], {'unique': 'True', 'max_length': '39'}),
+            'mac': ('maasserver.fields.MACAddressField', [], {}),
+            'nodegroup': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.NodeGroup']"})
+        },
+        u'maasserver.downloadprogress': {
+            'Meta': {'object_name': 'DownloadProgress'},
+            'bytes_downloaded': ('django.db.models.fields.IntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'error': ('django.db.models.fields.CharField', [], {'max_length': '1000', 'blank': 'True'}),
+            'filename': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'nodegroup': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.NodeGroup']"}),
+            'size': ('django.db.models.fields.IntegerField', [], {'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.event': {
+            'Meta': {'object_name': 'Event'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'description': ('django.db.models.fields.TextField', [], {'default': "u''", 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'node': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.Node']"}),
+            'type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.EventType']"}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.eventtype': {
+            'Meta': {'object_name': 'EventType'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'description': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'level': ('django.db.models.fields.IntegerField', [], {'db_index': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '255'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.filestorage': {
+            'Meta': {'unique_together': "((u'filename', u'owner'),)", 'object_name': 'FileStorage'},
+            'content': ('metadataserver.fields.BinaryField', [], {'blank': 'True'}),
+            'filename': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'default': "u'c4af88bc-2ae9-11e5-9139-00163edfc3e6'", 'unique': 'True', 'max_length': '36'}),
+            'owner': ('django.db.models.fields.related.ForeignKey', [], {'default': 'None', 'to': u"orm['auth.User']", 'null': 'True', 'blank': 'True'})
+        },
+        u'maasserver.filesystem': {
+            'Meta': {'object_name': 'Filesystem'},
+            'block_device': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.BlockDevice']", 'null': 'True', 'blank': 'True'}),
+            'create_params': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'filesystem_group': ('django.db.models.fields.related.ForeignKey', [], {'blank': 'True', 'related_name': "u'filesystems'", 'null': 'True', 'to': u"orm['maasserver.FilesystemGroup']"}),
+            'fstype': ('django.db.models.fields.CharField', [], {'default': "u'ext4'", 'max_length': '20'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mount_params': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'mount_point': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'partition': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.Partition']", 'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'uuid': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '36'})
+        },
+        u'maasserver.filesystemgroup': {
+            'Meta': {'object_name': 'FilesystemGroup'},
+            'create_params': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'group_type': ('django.db.models.fields.CharField', [], {'max_length': '20'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'uuid': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '36'})
+        },
+        u'maasserver.largefile': {
+            'Meta': {'object_name': 'LargeFile'},
+            'content': ('maasserver.fields.LargeObjectField', [], {}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'sha256': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '64'}),
+            'total_size': ('django.db.models.fields.BigIntegerField', [], {}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.licensekey': {
+            'Meta': {'unique_together': "((u'osystem', u'distro_series'),)", 'object_name': 'LicenseKey'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'distro_series': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'license_key': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'osystem': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.macaddress': {
+            'Meta': {'ordering': "(u'created',)", 'object_name': 'MACAddress'},
+            'cluster_interface': ('django.db.models.fields.related.ForeignKey', [], {'default': 'None', 'to': u"orm['maasserver.NodeGroupInterface']", 'null': 'True', 'on_delete': 'models.SET_NULL', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'ip_addresses': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['maasserver.StaticIPAddress']", 'symmetrical': 'False', 'through': u"orm['maasserver.MACStaticIPAddressLink']", 'blank': 'True'}),
+            'mac_address': ('maasserver.fields.MACAddressField', [], {'unique': 'True'}),
+            'networks': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['maasserver.Network']", 'symmetrical': 'False', 'blank': 'True'}),
+            'node': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.Node']", 'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.macstaticipaddresslink': {
+            'Meta': {'unique_together': "((u'ip_address', u'mac_address'),)", 'object_name': 'MACStaticIPAddressLink'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'ip_address': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.StaticIPAddress']", 'unique': 'True'}),
+            'mac_address': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.MACAddress']"}),
+            'nic_alias': ('django.db.models.fields.IntegerField', [], {'default': 'None', 'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.network': {
+            'Meta': {'object_name': 'Network'},
+            'default_gateway': ('maasserver.fields.MAASIPAddressField', [], {'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'description': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            'dns_servers': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'ip': ('maasserver.fields.MAASIPAddressField', [], {'unique': 'True', 'max_length': '39'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '255'}),
+            'netmask': ('maasserver.fields.MAASIPAddressField', [], {'max_length': '39'}),
+            'vlan_tag': ('django.db.models.fields.PositiveSmallIntegerField', [], {'unique': 'True', 'null': 'True', 'blank': 'True'})
+        },
+        u'maasserver.node': {
+            'Meta': {'object_name': 'Node'},
+            'agent_name': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'architecture': ('django.db.models.fields.CharField', [], {'max_length': '31', 'null': 'True', 'blank': 'True'}),
+            'boot_type': ('django.db.models.fields.CharField', [], {'default': "u'fastpath'", 'max_length': '20'}),
+            'cpu_count': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'disable_ipv4': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'distro_series': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '20', 'blank': 'True'}),
+            'error': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'blank': 'True'}),
+            'error_description': ('django.db.models.fields.TextField', [], {'default': "u''", 'blank': 'True'}),
+            'hostname': ('django.db.models.fields.CharField', [], {'default': "u''", 'unique': 'True', 'max_length': '255', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'installable': ('django.db.models.fields.BooleanField', [], {'default': 'True', 'db_index': 'True'}),
+            'license_key': ('django.db.models.fields.CharField', [], {'max_length': '30', 'null': 'True', 'blank': 'True'}),
+            'memory': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'netboot': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'nodegroup': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.NodeGroup']", 'null': 'True'}),
+            'osystem': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '20', 'blank': 'True'}),
+            'owner': ('django.db.models.fields.related.ForeignKey', [], {'default': 'None', 'to': u"orm['auth.User']", 'null': 'True', 'blank': 'True'}),
+            'parent': ('django.db.models.fields.related.ForeignKey', [], {'default': 'None', 'related_name': "u'children'", 'null': 'True', 'blank': 'True', 'to': u"orm['maasserver.Node']"}),
+            'power_parameters': ('maasserver.fields.JSONObjectField', [], {'default': "u''", 'max_length': '32768', 'blank': 'True'}),
+            'power_state': ('django.db.models.fields.CharField', [], {'default': "u'unknown'", 'max_length': '10'}),
+            'power_state_updated': ('django.db.models.fields.DateTimeField', [], {'default': 'None', 'null': 'True'}),
+            'power_type': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '10', 'blank': 'True'}),
+            'pxe_mac': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "u'+'", 'on_delete': 'models.SET_NULL', 'default': 'None', 'to': u"orm['maasserver.MACAddress']", 'blank': 'True', 'null': 'True'}),
+            'routers': ('djorm_pgarray.fields.ArrayField', [], {'default': 'None', 'dbtype': "u'macaddr'", 'null': 'True', 'blank': 'True'}),
+            'status': ('django.db.models.fields.IntegerField', [], {'default': '0', 'max_length': '10'}),
+            'swap_size': ('django.db.models.fields.BigIntegerField', [], {'default': 'None', 'null': 'True', 'blank': 'True'}),
+            'system_id': ('django.db.models.fields.CharField', [], {'default': "u'node-c4b17d70-2ae9-11e5-9139-00163edfc3e6'", 'unique': 'True', 'max_length': '41'}),
+            'tags': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['maasserver.Tag']", 'symmetrical': 'False'}),
+            'token': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['piston.Token']", 'null': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'zone': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.Zone']", 'on_delete': 'models.SET_DEFAULT'})
+        },
+        u'maasserver.nodegroup': {
+            'Meta': {'object_name': 'NodeGroup'},
+            'api_key': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '18'}),
+            'api_token': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['piston.Token']", 'unique': 'True'}),
+            'cluster_name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'default_disable_ipv4': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'dhcp_key': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'maas_url': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'blank': 'True'}),
+            'name': ('maasserver.models.nodegroup.DomainNameField', [], {'max_length': '80', 'blank': 'True'}),
+            'status': ('django.db.models.fields.IntegerField', [], {'default': '1'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'uuid': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '36'})
+        },
+        u'maasserver.nodegroupinterface': {
+            'Meta': {'unique_together': "((u'nodegroup', u'name'),)", 'object_name': 'NodeGroupInterface'},
+            'broadcast_ip': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'foreign_dhcp_ip': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'interface': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'blank': 'True'}),
+            'ip': ('maasserver.fields.MAASIPAddressField', [], {'max_length': '39'}),
+            'ip_range_high': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'ip_range_low': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'management': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'name': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'blank': 'True'}),
+            'nodegroup': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.NodeGroup']"}),
+            'router_ip': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'static_ip_range_high': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'static_ip_range_low': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'subnet_mask': ('maasserver.fields.MAASIPAddressField', [], {'default': 'None', 'max_length': '39', 'null': 'True', 'blank': 'True'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.partition': {
+            'Meta': {'object_name': 'Partition'},
+            'bootable': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'partition_table': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "u'partitions'", 'to': u"orm['maasserver.PartitionTable']"}),
+            'size': ('django.db.models.fields.BigIntegerField', [], {}),
+            'start_offset': ('django.db.models.fields.BigIntegerField', [], {}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'uuid': ('django.db.models.fields.CharField', [], {'max_length': '36', 'unique': 'True', 'null': 'True', 'blank': 'True'})
+        },
+        u'maasserver.partitiontable': {
+            'Meta': {'object_name': 'PartitionTable'},
+            'block_device': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['maasserver.BlockDevice']"}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'table_type': ('django.db.models.fields.CharField', [], {'default': "u'GPT'", 'max_length': '20'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.physicalblockdevice': {
+            'Meta': {'ordering': "[u'id']", 'object_name': 'PhysicalBlockDevice', '_ormbases': [u'maasserver.BlockDevice']},
+            u'blockdevice_ptr': ('django.db.models.fields.related.OneToOneField', [], {'to': u"orm['maasserver.BlockDevice']", 'unique': 'True', 'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '255', 'blank': 'True'}),
+            'serial': ('django.db.models.fields.CharField', [], {'max_length': '255', 'blank': 'True'})
+        },
+        u'maasserver.sshkey': {
+            'Meta': {'unique_together': "((u'user', u'key'),)", 'object_name': 'SSHKey'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.TextField', [], {}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['auth.User']"})
+        },
+        u'maasserver.sslkey': {
+            'Meta': {'unique_together': "((u'user', u'key'),)", 'object_name': 'SSLKey'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.TextField', [], {}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['auth.User']"})
+        },
+        u'maasserver.staticipaddress': {
+            'Meta': {'object_name': 'StaticIPAddress'},
+            'alloc_type': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'hostname': ('django.db.models.fields.CharField', [], {'default': "u''", 'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'ip': ('maasserver.fields.MAASIPAddressField', [], {'unique': 'True', 'max_length': '39'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'default': 'None', 'to': u"orm['auth.User']", 'null': 'True', 'blank': 'True'})
+        },
+        u'maasserver.tag': {
+            'Meta': {'object_name': 'Tag'},
+            'comment': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'definition': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'kernel_opts': ('django.db.models.fields.TextField', [], {'null': 'True', 'blank': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '256'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'maasserver.userprofile': {
+            'Meta': {'object_name': 'UserProfile'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'user': ('django.db.models.fields.related.OneToOneField', [], {'to': u"orm['auth.User']", 'unique': 'True'})
+        },
+        u'maasserver.virtualblockdevice': {
+            'Meta': {'ordering': "[u'id']", 'object_name': 'VirtualBlockDevice', '_ormbases': [u'maasserver.BlockDevice']},
+            u'blockdevice_ptr': ('django.db.models.fields.related.OneToOneField', [], {'to': u"orm['maasserver.BlockDevice']", 'unique': 'True', 'primary_key': 'True'}),
+            'filesystem_group': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "u'virtual_devices'", 'to': u"orm['maasserver.FilesystemGroup']"}),
+            'uuid': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '36'})
+        },
+        u'maasserver.zone': {
+            'Meta': {'ordering': "[u'name']", 'object_name': 'Zone'},
+            'created': ('django.db.models.fields.DateTimeField', [], {}),
+            'description': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '256'}),
+            'updated': ('django.db.models.fields.DateTimeField', [], {})
+        },
+        u'piston.consumer': {
+            'Meta': {'object_name': 'Consumer'},
+            'description': ('django.db.models.fields.TextField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '18'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '255'}),
+            'secret': ('django.db.models.fields.CharField', [], {'max_length': '32'}),
+            'status': ('django.db.models.fields.CharField', [], {'default': "'pending'", 'max_length': '16'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'blank': 'True', 'related_name': "'consumers'", 'null': 'True', 'to': u"orm['auth.User']"})
+        },
+        u'piston.token': {
+            'Meta': {'object_name': 'Token'},
+            'callback': ('django.db.models.fields.CharField', [], {'max_length': '255', 'null': 'True', 'blank': 'True'}),
+            'callback_confirmed': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'consumer': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['piston.Consumer']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_approved': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '18'}),
+            'secret': ('django.db.models.fields.CharField', [], {'max_length': '32'}),
+            'timestamp': ('django.db.models.fields.IntegerField', [], {'default': '1436961921L'}),
+            'token_type': ('django.db.models.fields.IntegerField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'blank': 'True', 'related_name': "'tokens'", 'null': 'True', 'to': u"orm['auth.User']"}),
+            'verifier': ('django.db.models.fields.CharField', [], {'max_length': '10'})
+        }
+    }
+
+    complete_apps = ['maasserver']
 
=== modified file 'src/maasserver/models/node.py'
--- src/maasserver/models/node.py	2015-05-22 15:03:29 +0000
+++ src/maasserver/models/node.py	2015-07-15 12:15:32 +0000
@@ -38,6 +38,7 @@
     BooleanField,
     CASCADE,
     CharField,
+    DateTimeField,
     ForeignKey,
     IntegerField,
     Manager,
@@ -91,7 +92,10 @@
 from maasserver.models.physicalblockdevice import PhysicalBlockDevice
 from maasserver.models.staticipaddress import StaticIPAddress
 from maasserver.models.tag import Tag
-from maasserver.models.timestampedmodel import TimestampedModel
+from maasserver.models.timestampedmodel import (
+    now,
+    TimestampedModel,
+)
 from maasserver.models.zone import Zone
 from maasserver.node_status import (
     COMMISSIONING_LIKE_STATUSES,
@@ -457,14 +461,19 @@
     power_type = CharField(
         max_length=10, null=False, blank=True, default='')
 
-    # JSON-encoded set of parameters for power control.
-    power_parameters = JSONObjectField(blank=True, default="")
+    # JSON-encoded set of parameters for power control, limited to 32kiB when
+    # encoded as JSON.
+    power_parameters = JSONObjectField(
+        max_length=(2 ** 15), blank=True, default="")
 
     power_state = CharField(
         max_length=10, null=False, blank=False,
         choices=POWER_STATE_CHOICES, default=POWER_STATE.UNKNOWN,
         editable=False)
 
+    power_state_updated = DateTimeField(
+        null=True, blank=False, default=None, editable=False)
+
     token = ForeignKey(
         Token, db_index=True, null=True, editable=False, unique=False)
 
@@ -1728,6 +1737,7 @@
     def update_power_state(self, power_state):
         """Update a node's power state """
         self.power_state = power_state
+        self.power_state_updated = now()
         mark_ready = (
             self.status == NODE_STATUS.RELEASING and
             power_state == POWER_STATE.OFF)
 
=== modified file 'src/maasserver/models/tests/test_node.py'
--- src/maasserver/models/tests/test_node.py	2015-05-26 07:38:51 +0000
+++ src/maasserver/models/tests/test_node.py	2015-07-15 12:15:32 +0000
@@ -63,6 +63,7 @@
 )
 from maasserver.models.node import PowerInfo
 from maasserver.models.staticipaddress import StaticIPAddress
+from maasserver.models.timestampedmodel import now
 from maasserver.models.user import create_auth_token
 from maasserver.node_status import (
     get_failed_status,
@@ -1837,6 +1838,13 @@
         node.update_power_state(state)
         self.assertEqual(state, reload_object(node).power_state)
 
+    def test_update_power_state_sets_last_updated_field(self):
+        node = factory.make_Node(power_state_updated=None)
+        self.assertIsNone(node.power_state_updated)
+        state = factory.pick_enum(POWER_STATE)
+        node.update_power_state(state)
+        self.assertEqual(now(), reload_object(node).power_state_updated)
+
     def test_update_power_state_readies_node_if_releasing(self):
         node = factory.make_Node(
             power_state=POWER_STATE.ON, status=NODE_STATUS.RELEASING,
 
=== modified file 'src/maasserver/models/timestampedmodel.py'
--- src/maasserver/models/timestampedmodel.py	2015-05-07 18:14:38 +0000
+++ src/maasserver/models/timestampedmodel.py	2015-07-15 12:15:32 +0000
@@ -13,6 +13,7 @@
 
 __metaclass__ = type
 __all__ = [
+    'now',
     'TimestampedModel',
     ]
 
 
=== modified file 'src/maasserver/rpc/nodes.py'
--- src/maasserver/rpc/nodes.py	2015-05-07 18:14:38 +0000
+++ src/maasserver/rpc/nodes.py	2015-07-15 12:15:32 +0000
@@ -19,6 +19,9 @@
     "create_node",
 ]
 
+from datetime import timedelta
+from itertools import chain
+
 from django.contrib.auth.models import User
 from django.core.exceptions import ValidationError
 from maasserver import exceptions
@@ -30,6 +33,7 @@
     Node,
     NodeGroup,
 )
+from maasserver.models.timestampedmodel import now
 from maasserver.utils.orm import transactional
 from provisioningserver.rpc.exceptions import (
     CommissionNodeFailed,
@@ -59,35 +63,97 @@
         raise NodeStateViolation(e)
 
 
-@synchronous
-@transactional
-def list_cluster_nodes_power_parameters(uuid):
-    """Query a cluster controller and return all of its nodes
-    power parameters
-
-    for :py:class:`~provisioningserver.rpc.region.ListNodePowerParameters`.
+def _gen_cluster_nodes_power_parameters(nodes):
+    """Generate power parameters for `nodes`.
+
+    These fulfil a subset of the return schema for the RPC call for
+    :py:class:`~provisioningserver.rpc.region.ListNodePowerParameters`.
+
+    :return: A generator yielding `dict`s.
     """
-    try:
-        nodegroup = NodeGroup.objects.get_by_natural_key(uuid)
-    except NodeGroup.DoesNotExist:
-        raise NoSuchCluster.from_uuid(uuid)
-    else:
-        power_info_by_node = (
-            (node, node.get_effective_power_info())
-            for node in nodegroup.node_set.exclude(
-                status=NODE_STATUS.BROKEN).exclude(installable=False)
-        )
-        return [
-            {
+    five_minutes_ago = now() - timedelta(minutes=5)
+
+    # This is meant to be temporary until all the power types support querying
+    # the power state of a node. See the definition of QUERY_POWER_TYPES for
+    # more information.
+    from provisioningserver.rpc.power import QUERY_POWER_TYPES
+
+    nodes_unchecked = (
+        nodes
+        .filter(power_state_updated=None)
+        .filter(power_type__in=QUERY_POWER_TYPES)
+        .exclude(status=NODE_STATUS.BROKEN)
+        .exclude(installable=False)
+    )
+    nodes_checked = (
+        nodes
+        .exclude(power_state_updated=None)
+        .exclude(power_state_updated__gt=five_minutes_ago)
+        .filter(power_type__in=QUERY_POWER_TYPES)
+        .exclude(status=NODE_STATUS.BROKEN)
+        .exclude(installable=False)
+        .order_by("power_state_updated", "system_id")
+    )
+
+    for node in chain(nodes_unchecked, nodes_checked):
+        power_info = node.get_effective_power_info()
+        if power_info.power_type is not None:
+            yield {
                 'system_id': node.system_id,
                 'hostname': node.hostname,
                 'power_state': node.power_state,
                 'power_type': power_info.power_type,
                 'context': power_info.power_parameters,
             }
-            for node, power_info in power_info_by_node
-            if power_info.power_type is not None
-        ]
+
+
+def _gen_up_to_json_limit(things, limit):
+    """Yield until the combined JSON dump of those things would exceed `limit`.
+
+    :param things: Any iterable whose elements can dumped as JSON.
+    :return: A generator that yields items from `things` unmodified, and in
+        order, though maybe not all of them.
+    """
+    # Deduct the space required for brackets. json.dumps(), by default, does
+    # not add padding, so it's just the opening and closing brackets.
+    limit -= 2
+
+    for index, thing in enumerate(things):
+        # Adjust the limit according the the size of thing.
+        if index == 0:
+            # A sole element does not need a delimiter.
+            limit -= len(json.dumps(thing))
+        else:
+            # There is a delimiter between this and the preceeding element.
+            # json.dumps(), by default, uses ", ", i.e. 2 characters.
+            limit -= len(json.dumps(thing)) + 2
+
+        # Check if we've reached the limit.
+        if limit == 0:
+            yield thing
+            break
+        elif limit > 0:
+            yield thing
+        else:
+            break
+
+
+@synchronous
+@transactional
+def list_cluster_nodes_power_parameters(uuid):
+    """Return power parameters for a cluster's nodes, in priority order.
+
+    For :py:class:`~provisioningserver.rpc.region.ListNodePowerParameters`.
+    """
+    try:
+        nodegroup = NodeGroup.objects.get_by_natural_key(uuid)
+    except NodeGroup.DoesNotExist:
+        raise NoSuchCluster.from_uuid(uuid)
+    else:
+        nodes = nodegroup.node_set.all()
+        details = _gen_cluster_nodes_power_parameters(nodes)
+        details = _gen_up_to_json_limit(details, 60 * (2 ** 10))  # 60kiB
+        return list(details)
 
 
 @synchronous
 
=== modified file 'src/maasserver/rpc/tests/test_nodes.py'
--- src/maasserver/rpc/tests/test_nodes.py	2015-05-22 15:52:13 +0000
+++ src/maasserver/rpc/tests/test_nodes.py	2015-07-15 12:15:32 +0000
@@ -14,10 +14,16 @@
 __metaclass__ = type
 __all__ = []
 
+from datetime import timedelta
+from itertools import imap
+import json
+from operator import attrgetter
 import random
+from random import randint
 
 from django.core.exceptions import ValidationError
 from maasserver.enum import NODE_STATUS
+from maasserver.models.timestampedmodel import now
 from maasserver.rpc.nodes import (
     commission_node,
     create_node,
@@ -47,12 +53,15 @@
     NodeStateViolation,
     NoSuchNode,
 )
+from provisioningserver.rpc.power import QUERY_POWER_TYPES
 from simplejson import dumps
 from testtools import ExpectedException
 from testtools.matchers import (
     Contains,
     Equals,
+    GreaterThan,
     Is,
+    LessThan,
     Not,
 )
 
@@ -321,25 +330,127 @@
     # Those tests have been left there for now because they also check
     # that the return values are being formatted correctly for RPC.
 
-    def test_does_not_return_power_info_for_broken_nodes(self):
-        cluster = factory.make_NodeGroup()
-        broken_node = factory.make_Node(
-            nodegroup=cluster, status=NODE_STATUS.BROKEN)
-
-        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
-        returned_system_ids = [
-            power_params['system_id'] for power_params in power_parameters]
-
-        self.assertThat(
-            returned_system_ids, Not(Contains(broken_node.system_id)))
-
-    def test_does_not_return_power_info_for_devices(self):
-        cluster = factory.make_NodeGroup()
-        device = factory.make_Device()
-
-        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
-        returned_system_ids = [
-            power_params['system_id'] for power_params in power_parameters]
-
-        self.assertThat(
-            returned_system_ids, Not(Contains(device.system_id)))
+    def make_Node(
+            self, cluster, power_type=None, power_state_updated=None,
+            **kwargs):
+        if power_type is None:
+            # Ensure that this node's power status can be queried.
+            power_type = random.choice(QUERY_POWER_TYPES)
+        if power_state_updated is None:
+            # Ensure that this node was last queried at least 5 minutes ago.
+            power_state_updated = now() - timedelta(minutes=randint(6, 16))
+        return factory.make_Node(
+            nodegroup=cluster, power_type=power_type,
+            power_state_updated=power_state_updated, **kwargs)
+
+    def test__returns_unchecked_nodes_first(self):
+        cluster = factory.make_NodeGroup()
+        nodes = [self.make_Node(cluster) for _ in xrange(5)]
+        node_unchecked = random.choice(nodes)
+        node_unchecked.power_state_updated = None
+        node_unchecked.save()
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        # The unchecked node is always the first out.
+        self.assertEqual(node_unchecked.system_id, system_ids[0])
+
+    def test__excludes_recently_checked_nodes(self):
+        cluster = factory.make_NodeGroup()
+
+        node_unchecked = self.make_Node(cluster)
+        node_unchecked.power_state_updated = None
+        node_unchecked.save()
+
+        datetime_now = now()
+        node_checked_recently = self.make_Node(cluster)
+        node_checked_recently.power_state_updated = datetime_now
+        node_checked_recently.save()
+
+        datetime_10_minutes_ago = datetime_now - timedelta(minutes=10)
+        node_checked_long_ago = self.make_Node(cluster)
+        node_checked_long_ago.power_state_updated = datetime_10_minutes_ago
+        node_checked_long_ago.save()
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        self.assertItemsEqual(
+            {node_unchecked.system_id, node_checked_long_ago.system_id},
+            system_ids)
+
+    def test__excludes_unqueryable_power_types(self):
+        cluster = factory.make_NodeGroup()
+        node_queryable = self.make_Node(cluster)
+        self.make_Node(cluster, "foobar")  # Unqueryable power type.
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        self.assertItemsEqual([node_queryable.system_id], system_ids)
+
+    def test__excludes_broken_nodes(self):
+        cluster = factory.make_NodeGroup()
+        node_queryable = self.make_Node(cluster)
+
+        self.make_Node(cluster, status=NODE_STATUS.BROKEN)
+        self.make_Node(
+            cluster, status=NODE_STATUS.BROKEN, power_state_updated=(
+                now() - timedelta(minutes=10)))
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        self.assertItemsEqual([node_queryable.system_id], system_ids)
+
+    def test__excludes_devices(self):
+        cluster = factory.make_NodeGroup()
+        node_queryable = self.make_Node(cluster)
+
+        factory.make_Device(nodegroup=cluster)
+        factory.make_Device(nodegroup=cluster, power_type="ipmi")
+        factory.make_Device(
+            nodegroup=cluster, power_type="ipmi", power_state_updated=(
+                now() - timedelta(minutes=10)))
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        self.assertItemsEqual([node_queryable.system_id], system_ids)
+
+    def test__returns_checked_nodes_in_last_checked_order(self):
+        cluster = factory.make_NodeGroup()
+        nodes = [self.make_Node(cluster) for _ in xrange(5)]
+
+        power_parameters = list_cluster_nodes_power_parameters(cluster.uuid)
+        system_ids = [params["system_id"] for params in power_parameters]
+
+        # Checked nodes are always sorted from least recently checked to most.
+        node_sort_key = attrgetter("power_state_updated", "system_id")
+        nodes_in_order = sorted(nodes, key=node_sort_key)
+        self.assertEqual(
+            [node.system_id for node in nodes_in_order],
+            system_ids)
+
+    def test__returns_at_most_60kiB_of_JSON(self):
+        cluster = factory.make_NodeGroup()
+
+        # Ensure that there are at least 64kiB of power parameters (when
+        # converted to JSON) in the database.
+        example_parameters = {"key%d" % i: "value%d" % i for i in xrange(100)}
+        remaining = 2 ** 16
+        while remaining > 0:
+            node = self.make_Node(cluster, power_parameters=example_parameters)
+            remaining -= len(json.dumps(node.get_effective_power_parameters()))
+
+        nodes = list_cluster_nodes_power_parameters(cluster.uuid)
+
+        # The total size of the JSON is less than 60kiB, but only a bit.
+        nodes_json = imap(json.dumps, nodes)
+        nodes_json_lengths = imap(len, nodes_json)
+        nodes_json_length = sum(nodes_json_lengths)
+        expected_maximum = 60 * (2 ** 10)  # 60kiB
+        self.expectThat(nodes_json_length, LessThan(expected_maximum + 1))
+        expected_minimum = 50 * (2 ** 10)  # 50kiB
+        self.expectThat(nodes_json_length, GreaterThan(expected_minimum - 1))
 
=== modified file 'src/maasserver/rpc/tests/test_regionservice.py'
--- src/maasserver/rpc/tests/test_regionservice.py	2015-06-05 13:21:13 +0000
+++ src/maasserver/rpc/tests/test_regionservice.py	2015-07-15 12:15:32 +0000
@@ -104,6 +104,7 @@
     NoSuchNode,
 )
 from provisioningserver.rpc.interfaces import IConnection
+from provisioningserver.rpc.power import QUERY_POWER_TYPES
 from provisioningserver.rpc.region import (
     Authenticate,
     CommissionNode,
@@ -688,7 +689,10 @@
         nodegroup = yield deferToThread(self.create_nodegroup)
         nodes = []
         for _ in range(3):
-            node = yield deferToThread(self.create_node, nodegroup)
+            node = yield deferToThread(
+                self.create_node, nodegroup,
+                power_type=random.choice(QUERY_POWER_TYPES),
+                power_state_updated=None)
             power_params = yield deferToThread(
                 self.get_node_power_parameters, node)
             nodes.append({
@@ -701,12 +705,15 @@
 
         # Create a node with an invalid power type (i.e. the empty string).
         # This will not be reported by the call to ListNodePowerParameters.
-        yield deferToThread(self.create_node, nodegroup, power_type="")
+        yield deferToThread(
+            self.create_node, nodegroup, power_type="",
+            power_state_updated=None)
 
         response = yield call_responder(
             Region(), ListNodePowerParameters,
             {b'uuid': nodegroup.uuid})
 
+        self.maxDiff = None
         self.assertItemsEqual(nodes, response['nodes'])
 
     @wait_for_reactor
 
=== modified file 'src/maasserver/testing/factory.py'
--- src/maasserver/testing/factory.py	2015-05-20 13:51:49 +0000
+++ src/maasserver/testing/factory.py	2015-07-15 12:15:32 +0000
@@ -17,6 +17,7 @@
     "Messages",
     ]
 
+from datetime import timedelta
 import hashlib
 from io import BytesIO
 import logging
@@ -25,6 +26,7 @@
 
 from django.contrib.auth.models import User
 from django.test.client import RequestFactory
+from django.utils import timezone
 from maasserver.clusterrpc.power_parameters import get_power_types
 from maasserver.enum import (
     BOOT_RESOURCE_FILE_TYPE,
@@ -107,6 +109,11 @@
 ALL_NODE_STATES = map_enum(NODE_STATUS).values()
 
 
+# Use `undefined` instead of `None` for default factory arguments when `None`
+# is a reasonable value for the argument.
+undefined = object()
+
+
 class Messages:
     """A class to record messages published by Django messaging
     framework.
@@ -231,12 +238,13 @@
         device.save()
         return device
 
-    def make_Node(self, mac=False, hostname=None, status=None,
-                  architecture="i386/generic", installable=True, updated=None,
-                  created=None, nodegroup=None, routers=None, zone=None,
-                  power_type=None, networks=None, boot_type=None,
-                  sortable_name=False, parent=None, power_state=None,
-                  disable_ipv4=None, **kwargs):
+    def make_Node(
+            self, mac=False, hostname=None, status=None,
+            architecture="i386/generic", installable=True, updated=None,
+            created=None, nodegroup=None, routers=None, zone=None,
+            networks=None, boot_type=None, sortable_name=False,
+            power_type=None, power_parameters=None, power_state=None,
+            power_state_updated=undefined, disable_ipv4=None, **kwargs):
         """Make a :class:`Node`.
 
         :param sortable_name: If `True`, use a that will sort consistently
@@ -260,8 +268,13 @@
             zone = self.make_Zone()
         if power_type is None:
             power_type = 'ether_wake'
+        if power_parameters is None:
+            power_parameters = ""
         if power_state is None:
             power_state = self.pick_enum(POWER_STATE)
+        if power_state_updated is undefined:
+            power_state_updated = (
+                timezone.now() - timedelta(minutes=random.randint(0, 15)))
         if disable_ipv4 is None:
             disable_ipv4 = self.pick_bool()
         if boot_type is None:
@@ -269,9 +282,10 @@
         node = Node(
             hostname=hostname, status=status, architecture=architecture,
             installable=installable, nodegroup=nodegroup, routers=routers,
-            zone=zone, power_type=power_type, disable_ipv4=disable_ipv4,
-            parent=parent, boot_type=boot_type, power_state=power_state,
-            **kwargs)
+            zone=zone, boot_type=boot_type, power_type=power_type,
+            power_parameters=power_parameters, power_state=power_state,
+            power_state_updated=power_state_updated,
+            disable_ipv4=disable_ipv4, **kwargs)
         self._save_node_unchecked(node)
         # We do not generate random networks by default because the limited
         # number of VLAN identifiers (4,094) makes it very likely to
 
=== modified file 'src/maasserver/websockets/handlers/device.py'
--- src/maasserver/websockets/handlers/device.py	2015-05-27 16:17:55 +0000
+++ src/maasserver/websockets/handlers/device.py	2015-07-15 12:15:32 +0000
@@ -139,6 +139,7 @@
             "boot_type",
             "status",
             "power_parameters",
+            "power_state_updated",
             "disable_ipv4",
             "osystem",
             "power_type",
 
=== modified file 'src/maasserver/websockets/handlers/node.py'
--- src/maasserver/websockets/handlers/node.py	2015-07-10 09:08:58 +0000
+++ src/maasserver/websockets/handlers/node.py	2015-07-15 12:15:32 +0000
@@ -95,6 +95,9 @@
             "token",
             "netboot",
             "agent_name",
+            # power_state_updated isn't needed in the client yet, plus it's
+            # not native to JSON. Omit for now.
+            "power_state_updated",
         ]
         list_fields = [
             "system_id",
 
=== modified file 'src/provisioningserver/pserv_services/node_power_monitor_service.py'
--- src/provisioningserver/pserv_services/node_power_monitor_service.py	2015-05-07 18:14:38 +0000
+++ src/provisioningserver/pserv_services/node_power_monitor_service.py	2015-07-15 12:15:32 +0000
@@ -27,10 +27,6 @@
 )
 from provisioningserver.rpc.power import query_all_nodes
 from provisioningserver.rpc.region import ListNodePowerParameters
-from provisioningserver.utils.twisted import (
-    pause,
-    retries,
-)
 from twisted.application.internet import TimerService
 from twisted.internet.defer import inlineCallbacks
 from twisted.python import log
@@ -42,7 +38,7 @@
 class NodePowerMonitorService(TimerService, object):
     """Service to monitor the power status of all nodes in this cluster."""
 
-    check_interval = timedelta(minutes=5).total_seconds()
+    check_interval = timedelta(seconds=15).total_seconds()
     max_nodes_at_once = 5
 
     def __init__(self, cluster_uuid, clock=None):
@@ -57,42 +53,38 @@
         Log errors on failure, but do not propagate them up; that will
         stop the timed loop from running.
         """
-        def query_nodes_failed(failure):
+        try:
+            client = getRegionClient()
+        except NoConnectionsAvailable:
+            maaslog.debug(
+                "Cannot monitor nodes' power status; "
+                "region not available.")
+        else:
+            d = self.query_nodes(client, uuid)
+            d.addErrback(self.query_nodes_failed, uuid)
+            return d
+
+    @inlineCallbacks
+    def query_nodes(self, client, uuid):
+        # Get the nodes' power parameters from the region. Keep getting more
+        # power parameters until the region returns an empty list.
+        while True:
+            response = yield client(ListNodePowerParameters, uuid=uuid)
+            power_parameters = response['nodes']
+            if len(power_parameters) > 0:
+                yield query_all_nodes(
+                    power_parameters, max_concurrency=self.max_nodes_at_once,
+                    clock=self.clock)
+            else:
+                break
+
+    def query_nodes_failed(self, failure, uuid):
+        if failure.check(NoSuchCluster):
+            maaslog.error("Cluster %s is not recognised.", uuid)
+        else:
             # Log the error in full to the Twisted log.
-            log.err(failure)
+            log.err(failure, "Querying node power states.")
             # Log something concise to the MAAS log.
             maaslog.error(
                 "Failed to query nodes' power status: %s",
                 failure.getErrorMessage())
-
-        return self.query_nodes(uuid).addErrback(query_nodes_failed)
-
-    @inlineCallbacks
-    def query_nodes(self, uuid):
-        # Retry a few times, since this service usually comes up before
-        # the RPC service.
-        for elapsed, remaining, wait in retries(15, 5, self.clock):
-            try:
-                client = getRegionClient()
-            except NoConnectionsAvailable:
-                yield pause(wait, self.clock)
-            else:
-                break
-        else:
-            maaslog.error(
-                "Cannot monitor nodes' power status; "
-                "region not available.")
-            return
-
-        # Get the nodes' power parameters from the region.
-        try:
-            response = yield client(ListNodePowerParameters, uuid=uuid)
-        except NoSuchCluster:
-            maaslog.error(
-                "This cluster (%s) is not recognised by the region.",
-                uuid)
-        else:
-            node_power_parameters = response['nodes']
-            yield query_all_nodes(
-                node_power_parameters,
-                max_concurrency=self.max_nodes_at_once, clock=self.clock)
 
=== modified file 'src/provisioningserver/pserv_services/tests/test_node_power_monitor_service.py'
--- src/provisioningserver/pserv_services/tests/test_node_power_monitor_service.py	2015-05-22 15:52:13 +0000
+++ src/provisioningserver/pserv_services/tests/test_node_power_monitor_service.py	2015-07-15 12:15:32 +0000
@@ -17,10 +17,7 @@
 
 from fixtures import FakeLogger
 from maastesting.factory import factory
-from maastesting.matchers import (
-    MockCalledOnceWith,
-    MockCallsMatch,
-)
+from maastesting.matchers import MockCalledOnceWith
 from maastesting.testcase import (
     MAASTestCase,
     MAASTwistedRunTest,
@@ -28,13 +25,14 @@
 from maastesting.twisted import TwistedLoggerFixture
 from mock import (
     ANY,
-    call,
+    sentinel,
 )
 from provisioningserver.pserv_services import (
     node_power_monitor_service as npms,
 )
 from provisioningserver.rpc import (
     exceptions,
+    getRegionClient,
     region,
 )
 from provisioningserver.rpc.testing import MockClusterToRegionRPCFixture
@@ -56,94 +54,84 @@
         service = npms.NodePowerMonitorService(cluster_uuid)
         self.assertThat(service, MatchesStructure.byEquality(
             call=(service.try_query_nodes, (cluster_uuid,), {}),
-            step=(5 * 60), clock=None))
+            step=15, clock=None))
 
     def make_monitor_service(self):
         cluster_uuid = factory.make_UUID()
         service = npms.NodePowerMonitorService(cluster_uuid, Clock())
         return cluster_uuid, service
 
-    def test_query_nodes_retries_getting_client(self):
-        cluster_uuid, service = self.make_monitor_service()
-
-        getRegionClient = self.patch(npms, "getRegionClient")
-        getRegionClient.side_effect = exceptions.NoConnectionsAvailable
-
-        def has_been_called_n_times(n):
-            calls = [call()] * n
-            return MockCallsMatch(*calls)
-
-        maaslog = self.useFixture(FakeLogger("maas"))
-
-        d = service.query_nodes(cluster_uuid)
-        # Immediately the first attempt to get a client happens.
-        self.assertThat(getRegionClient, has_been_called_n_times(1))
-        self.assertFalse(d.called)
-        # Followed by 3 more attempts as time passes.
-        service.clock.pump((5, 5, 5))
-        self.assertThat(getRegionClient, has_been_called_n_times(4))
-        # query_nodes returns after 15 seconds.
-        self.assertTrue(d.called)
-        self.assertIsNone(extract_result(d))
-
-        # A simple message is logged, but even this may be too noisy.
-        self.assertIn(
-            "Cannot monitor nodes' power status; region not available.",
-            maaslog.output)
-
     def test_query_nodes_calls_the_region(self):
         cluster_uuid, service = self.make_monitor_service()
 
         rpc_fixture = self.useFixture(MockClusterToRegionRPCFixture())
-        client, io = rpc_fixture.makeEventLoop(region.ListNodePowerParameters)
-        client.ListNodePowerParameters.return_value = succeed({"nodes": []})
+        proto_region, io = rpc_fixture.makeEventLoop(
+            region.ListNodePowerParameters)
+        proto_region.ListNodePowerParameters.return_value = succeed(
+            {"nodes": []})
 
-        d = service.query_nodes(cluster_uuid)
+        d = service.query_nodes(getRegionClient(), cluster_uuid)
         io.flush()
 
         self.assertEqual(None, extract_result(d))
         self.assertThat(
-            client.ListNodePowerParameters,
+            proto_region.ListNodePowerParameters,
             MockCalledOnceWith(ANY, uuid=cluster_uuid))
 
     def test_query_nodes_calls_query_all_nodes(self):
         cluster_uuid, service = self.make_monitor_service()
+        service.max_nodes_at_once = sentinel.max_nodes_at_once
+
+        example_power_parameters = {
+            "system_id": factory.make_UUID(),
+            "hostname": factory.make_hostname(),
+            "power_state": factory.make_name("power_state"),
+            "power_type": factory.make_name("power_type"),
+            "context": {},
+        }
 
         rpc_fixture = self.useFixture(MockClusterToRegionRPCFixture())
-        client, io = rpc_fixture.makeEventLoop(region.ListNodePowerParameters)
-        client.ListNodePowerParameters.return_value = succeed({"nodes": []})
+        proto_region, io = rpc_fixture.makeEventLoop(
+            region.ListNodePowerParameters)
+        proto_region.ListNodePowerParameters.side_effect = [
+            succeed({"nodes": [example_power_parameters]}),
+            succeed({"nodes": []}),
+        ]
 
         query_all_nodes = self.patch(npms, "query_all_nodes")
 
-        d = service.query_nodes(cluster_uuid)
+        d = service.query_nodes(getRegionClient(), cluster_uuid)
         io.flush()
 
         self.assertEqual(None, extract_result(d))
         self.assertThat(
             query_all_nodes,
             MockCalledOnceWith(
-                [], max_concurrency=service.max_nodes_at_once,
+                [example_power_parameters],
+                max_concurrency=sentinel.max_nodes_at_once,
                 clock=service.clock))
 
     def test_query_nodes_copes_with_NoSuchCluster(self):
         cluster_uuid, service = self.make_monitor_service()
 
         rpc_fixture = self.useFixture(MockClusterToRegionRPCFixture())
-        client, io = rpc_fixture.makeEventLoop(region.ListNodePowerParameters)
-        client.ListNodePowerParameters.return_value = fail(
+        proto_region, io = rpc_fixture.makeEventLoop(
+            region.ListNodePowerParameters)
+        proto_region.ListNodePowerParameters.return_value = fail(
             exceptions.NoSuchCluster.from_uuid(cluster_uuid))
 
-        d = service.query_nodes(cluster_uuid)
+        d = service.query_nodes(getRegionClient(), cluster_uuid)
+        d.addErrback(service.query_nodes_failed, cluster_uuid)
         with FakeLogger("maas") as maaslog:
             io.flush()
 
         self.assertEqual(None, extract_result(d))
         self.assertDocTestMatches(
-            "This cluster (...) is not recognised by the region.",
-            maaslog.output)
+            "Cluster ... is not recognised.", maaslog.output)
 
     def test_try_query_nodes_logs_other_errors(self):
         cluster_uuid, service = self.make_monitor_service()
+        self.patch(npms, "getRegionClient").return_value = sentinel.client
 
         query_nodes = self.patch(service, "query_nodes")
         query_nodes.return_value = fail(
 
=== modified file 'src/provisioningserver/rpc/power.py'
--- src/provisioningserver/rpc/power.py	2015-07-10 09:08:58 +0000
+++ src/provisioningserver/rpc/power.py	2015-07-15 12:15:32 +0000
@@ -19,6 +19,7 @@
 
 from datetime import timedelta
 from functools import partial
+import sys
 
 from provisioningserver.events import (
     EVENT_TYPES,
@@ -331,33 +332,38 @@
         # type, however this is left here to prevent PEBKAC.
         raise PowerActionFail("Unknown power_type '%s'" % power_type)
 
+    def check_power_state(state):
+        if state not in ("on", "off", "unknown"):
+            # This is considered an error.
+            raise PowerActionFail(state)
+
+    # Capture errors as we go along.
+    exc_info = None, None, None
+
     # Use increasing waiting times to work around race conditions that could
     # arise when power querying the node.
     for waiting_time in default_waiting_policy:
-        error = None
         # Perform power query.
         try:
             power_state = yield deferToThread(
-                perform_power_query, system_id, hostname, power_type, context)
-            if power_state not in ("on", "off", "unknown"):
-                # This is considered an error.
-                raise PowerActionFail(power_state)
-        except PowerActionFail as e:
-            # Hold the error so if failure after retries, we can
-            # log the reason.
-            error = e
-
+                perform_power_query, system_id, hostname,
+                power_type, context)
+            check_power_state(power_state)
+        except:
+            # Hold the error; it may be reported later.
+            exc_info = sys.exc_info()
             # Wait before trying again.
             yield pause(waiting_time, clock)
-            continue
-        yield power_state_update(system_id, power_state)
-        returnValue(power_state)
+        else:
+            yield power_state_update(system_id, power_state)
+            returnValue(power_state)
 
-    # Send node is broken, since query failed after the multiple retries.
-    message = "Node could not be queried %s (%s) %s" % (
-        system_id, hostname, error)
+    # Reaching here means that things have gone wrong.
+    assert exc_info != (None, None, None)
+    exc_type, exc_value, exc_trace = exc_info
+    message = "Power state could not be queried: %s" % (exc_value,)
     yield power_query_failure(system_id, hostname, message)
-    raise PowerActionFail(error)
+    raise exc_type, exc_value, exc_trace
 
 
 def maaslog_report_success(node, power_state):
 
=== modified file 'src/provisioningserver/rpc/region.py'
--- src/provisioningserver/rpc/region.py	2015-05-07 18:14:38 +0000
+++ src/provisioningserver/rpc/region.py	2015-07-15 12:15:32 +0000
@@ -246,11 +246,16 @@
 
 
 class ListNodePowerParameters(amp.Command):
-    """Return the list of power parameters for nodes
-    that this cluster controls.
-
-    Used to query all of the nodes that the cluster
-    composes.
+    """Return power parameters for the nodes in the specified cluster.
+
+    This will only return power parameters for nodes that have power types for
+    which MAAS has a query capability.
+
+    It will return nodes in priority order. Those nodes at the beginning of
+    the list should be queried first.
+
+    It may return an empty list. This means that all nodes have been recently
+    queried. Take a break before asking again.
 
     :since: 1.7
     """
 
=== modified file 'src/provisioningserver/rpc/tests/test_power.py'
--- src/provisioningserver/rpc/tests/test_power.py	2015-05-22 15:52:13 +0000
+++ src/provisioningserver/rpc/tests/test_power.py	2015-07-15 12:15:32 +0000
@@ -30,6 +30,7 @@
     MAASTwistedRunTest,
 )
 from maastesting.twisted import (
+    always_fail_with,
     always_succeed_with,
     TwistedLoggerFixture,
 )
@@ -41,6 +42,7 @@
     sentinel,
 )
 import provisioningserver
+from provisioningserver.drivers.power import PowerDriverRegistry
 from provisioningserver.events import EVENT_TYPES
 from provisioningserver.power.poweraction import PowerActionFail
 from provisioningserver.rpc import (
@@ -643,6 +645,79 @@
         self.assertEqual("off", extract_result(d))
 
 
+class TestPowerQueryExceptions(MAASTestCase):
+
+    scenarios = tuple(
+        (power_type, {
+            "power_type": power_type,
+            "func": (  # Function to invoke driver.
+                "perform_power_driver_query"
+                if power_type in PowerDriverRegistry
+                else "perform_power_query"),
+            "waits": (  # Pauses between retries.
+                [] if power_type in PowerDriverRegistry
+                else power.default_waiting_policy),
+            "calls": (  # No. of calls to the driver.
+                1 if power_type in PowerDriverRegistry
+                else len(power.default_waiting_policy)),
+        })
+        for power_type in power.QUERY_POWER_TYPES
+    )
+
+    def test_get_power_state_captures_all_exceptions(self):
+        logger_twisted = self.useFixture(TwistedLoggerFixture())
+        logger_maaslog = self.useFixture(FakeLogger("maas"))
+
+        # Avoid threads here.
+        self.patch(power, "deferToThread", maybeDeferred)
+
+        exception_type = factory.make_exception_type()
+        exception_message = factory.make_string()
+        exception = exception_type(exception_message)
+
+        # Pretend the query always fails with `exception`.
+        query = self.patch_autospec(power, self.func)
+        query.side_effect = always_fail_with(exception)
+
+        # Intercept calls to power_query_failure().
+        self.patch_autospec(power, "power_query_failure")
+
+        system_id = factory.make_name('system_id')
+        hostname = factory.make_name('hostname')
+        context = sentinel.context
+        clock = Clock()
+
+        d = power.get_power_state(
+            system_id, hostname, self.power_type, context, clock)
+
+        # Crank through some number of retries.
+        for wait in self.waits:
+            self.assertFalse(d.called)
+            clock.advance(wait)
+        self.assertTrue(d.called)
+
+        # Finally the exception from the query is raised.
+        self.assertRaises(exception_type, extract_result, d)
+
+        # The broken power query function patched earlier was called the same
+        # number of times as there are steps in the default waiting policy.
+        expected_call = call(system_id, hostname, self.power_type, context)
+        expected_calls = [expected_call] * self.calls
+        self.assertThat(query, MockCallsMatch(*expected_calls))
+
+        # power_query_failure() was called once at the end with a message
+        # constructed using the error message we fabricated at the beginning.
+        expected_message = (
+            "Power state could not be queried: %s" % exception_message)
+        self.assertThat(power.power_query_failure, MockCalledOnceWith(
+            system_id, hostname, expected_message))
+
+        # Nothing was logged to the Twisted log or to maaslog; that happens
+        # elsewhere, in maaslog_query_failure() and maaslog_query().
+        self.assertEqual("", logger_twisted.output)
+        self.assertEqual("", logger_maaslog.output)
+
+
 class TestPowerQueryAsync(MAASTestCase):
 
     run_tests_with = MAASTwistedRunTest.make_factory(timeout=5)