diff --git a/distil/collector/base.py b/distil/collector/base.py
index 0578eb0..ec6f874 100644
--- a/distil/collector/base.py
+++ b/distil/collector/base.py
@@ -13,6 +13,7 @@
 #    under the License.
 
 import abc
+from datetime import timedelta
 import re
 import yaml
 
@@ -64,11 +65,16 @@ class BaseCollector(object):
             resources = {}
             usage_entries = []
 
+            # NOTE(kong): Set 10min as leadin time when getting samples, this
+            # helps us to get correct instance uptime, in case the instance
+            # status in first sample is not in our tracked status list.
+            actual_start = window_start - timedelta(minutes=10)
+
             try:
                 for mapping in self.meter_mappings:
                     # Invoke get_meter function of specific collector.
                     usage = self.get_meter(project['id'], mapping['meter'],
-                                           window_start, window_end)
+                                           actual_start, window_end)
 
                     usage_by_resource = {}
                     self._filter_and_group(usage, usage_by_resource)
@@ -125,7 +131,9 @@ class BaseCollector(object):
                 os_distro = image_meta.get('os_distro', 'unknown')
             else:
                 # Boot from image
-                image_id = entry['metadata']['image.id']
+                image_id = entry['metadata'].get('image.id', None)
+                image_id = image_id or entry['metadata'].get('image_ref', None)
+
                 os_distro = getattr(
                     openstack.get_image(image_id),
                     'os_distro',
@@ -180,6 +188,11 @@ class BaseCollector(object):
                 service, entries, window_start, window_end
             )
 
+            LOG.debug(
+                'After transformation, usage for resource %s: %s' %
+                (res_id, transformed)
+            )
+
             if transformed:
                 res_id = mapping.get('res_id_template', '%s') % res_id
                 res_info = self._get_resource_info(
@@ -192,7 +205,6 @@ class BaseCollector(object):
 
                 res = resources.setdefault(res_id, res_info)
                 res.update(res_info)
-                LOG.debug('resource info: %s', res)
 
                 for service, volume in transformed.items():
                     entry = {
@@ -205,4 +217,3 @@ class BaseCollector(object):
                         'tenant_id': project_id
                     }
                     usage_entries.append(entry)
-                    LOG.debug('new entry: %s', entry)
diff --git a/distil/common/general.py b/distil/common/general.py
index 8a2061a..d093d1c 100644
--- a/distil/common/general.py
+++ b/distil/common/general.py
@@ -17,6 +17,7 @@ from datetime import timedelta
 from decimal import Decimal
 import functools
 import math
+import socket
 import warnings
 import yaml
 
@@ -101,3 +102,8 @@ def convert_to(value, from_unit, to_unit):
     if from_unit == to_unit:
         return value
     return conversions[from_unit][to_unit](value)
+
+
+def get_process_identifier():
+    """Gets current running process identifier."""
+    return "%s_%s" % (socket.gethostname(), CONF.collector.partitioning_suffix)
diff --git a/distil/config.py b/distil/config.py
index e3f485c..a01d896 100644
--- a/distil/config.py
+++ b/distil/config.py
@@ -16,6 +16,7 @@ from keystoneauth1 import loading as ka_loading
 from oslo_cache import core as cache
 from oslo_config import cfg
 from oslo_log import log
+from oslo_utils import uuidutils
 
 from distil import version
 
@@ -65,6 +66,9 @@ COLLECTOR_OPTS = [
                 help=('The list of resources that handled by collector.')),
     cfg.StrOpt('dawn_of_time', default='2014-04-01 00:00:00',
                help=('The earlist starting time for new tenant.')),
+    cfg.StrOpt('partitioning_suffix',
+               help=('Collector partitioning group suffix. It is used when '
+                     'running multiple collectors in favor of lock.'))
 ]
 
 ODOO_OPTS = [
diff --git a/distil/db/api.py b/distil/db/api.py
index c1170e9..02ef0fa 100644
--- a/distil/db/api.py
+++ b/distil/db/api.py
@@ -31,6 +31,7 @@ interface.
                   `sqlite:///var/lib/distil/distil.sqlite`.
 
 """
+import contextlib
 
 from oslo_config import cfg
 from oslo_db import api as db_api
@@ -119,3 +120,27 @@ def project_get(project_id):
 
 def project_get_all():
     return IMPL.project_get_all()
+
+
+# Project Locks.
+
+def create_project_lock(project_id, owner):
+    return IMPL.create_project_lock(project_id, owner)
+
+
+def get_project_locks(project_id):
+    return IMPL.get_project_locks(project_id)
+
+
+def ensure_project_lock(project_id, owner):
+    return IMPL.ensure_project_lock(project_id, owner)
+
+
+def delete_project_lock(project_id):
+    return IMPL.delete_project_lock(project_id)
+
+
+@contextlib.contextmanager
+def project_lock(project_id, owner):
+    with IMPL.project_lock(project_id, owner):
+        yield
diff --git a/distil/db/migration/alembic_migrations/versions/002_add_project_lock_table.py b/distil/db/migration/alembic_migrations/versions/002_add_project_lock_table.py
new file mode 100644
index 0000000..40ef64b
--- /dev/null
+++ b/distil/db/migration/alembic_migrations/versions/002_add_project_lock_table.py
@@ -0,0 +1,39 @@
+# Copyright 2017 OpenStack Foundation.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""add-project-lock-table
+
+Revision ID: 002
+Revises: 001
+Create Date: 2017-01-11 11:45:05.107888
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '002'
+down_revision = '001'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    op.create_table(
+        'project_locks',
+        sa.Column('created', sa.DateTime(), nullable=False),
+        sa.Column('project_id', sa.String(length=100), nullable=False),
+        sa.Column('owner', sa.String(length=100), nullable=False),
+        sa.PrimaryKeyConstraint('project_id'),
+    )
diff --git a/distil/db/sqlalchemy/api.py b/distil/db/sqlalchemy/api.py
index b73dbc3..8059a64 100644
--- a/distil/db/sqlalchemy/api.py
+++ b/distil/db/sqlalchemy/api.py
@@ -15,21 +15,23 @@
 
 """Implementation of SQLAlchemy backend."""
 
+import contextlib
 from datetime import datetime
 import json
-import six
 import sys
-
-import sqlalchemy as sa
-from sqlalchemy import func
 import threading
 
 from oslo_config import cfg
 from oslo_db import exception as db_exception
 from oslo_db.sqlalchemy import session as db_session
 from oslo_log import log as logging
+from retrying import retry
+import six
+import sqlalchemy as sa
+from sqlalchemy import func
 
 from distil.db.sqlalchemy import models as m
+from distil.db.sqlalchemy.models import ProjectLock
 from distil.db.sqlalchemy.models import Resource
 from distil.db.sqlalchemy.models import Tenant
 from distil.db.sqlalchemy.models import UsageEntry
@@ -76,7 +78,7 @@ def get_backend():
 def setup_db():
     try:
         engine = get_engine()
-        m.Cluster.metadata.create_all(engine)
+        m.Tenant.metadata.create_all(engine)
     except sa.exc.OperationalError as e:
         LOG.exception("Database registration exception: %s", e)
         return False
@@ -226,8 +228,9 @@ def usages_add(project_id, resources, usage_entries, last_collect):
             for (id, res_info) in six.iteritems(resources):
                 res_db = _get_resource(session, project_id, id)
                 if res_db:
-                    orig_info = json.loads(res_db.info)
-                    res_db.info = json.dumps(orig_info.update(res_info))
+                    orig_info = json.loads(res_db.info) or {}
+                    orig_info.update(res_info)
+                    res_db.info = json.dumps(orig_info)
                 else:
                     resource_ref = Resource(
                         id=id,
@@ -306,3 +309,82 @@ def _merge_resource_metadata(md_dict, entry, md_def):
                 pass
 
     return md_dict
+
+
+def get_project_locks(project_id):
+    session = get_session()
+
+    query = session.query(ProjectLock)
+    query = query.filter(ProjectLock.project_id == project_id)
+
+    try:
+        return query.all()
+    except Exception as e:
+        raise exceptions.DBException(
+            "Failed when querying database, error type: %s, "
+            "error message: %s" % (e.__class__.__name__, str(e))
+        )
+
+
+@retry(stop_max_attempt_number=3, wait_fixed=5000)
+def create_project_lock(project_id, owner):
+    """Creates project lock record.
+
+    This method has to work without SQLAlchemy session because session may not
+    immediately issue an SQL query to a database and instead just schedule it
+    whereas we need to make sure to issue a operation immediately.
+
+    If there are more than 2 transactions trying to get same project lock
+    (although with little chance), after the first one's commit, only one of
+    the others will succeed to continue, all others will fail with exception.
+    Using retry mechanism here to avoid that happen.
+    """
+    session = get_session()
+    session.flush()
+
+    insert = ProjectLock.__table__.insert()
+    session.execute(insert.values(project_id=project_id, owner=owner,
+                                  created=datetime.utcnow()))
+
+    session.flush()
+
+
+def ensure_project_lock(project_id, owner):
+    """Make sure project lock record exists."""
+    session = get_session()
+
+    query = session.query(ProjectLock)
+    query = query.filter(ProjectLock.project_id == project_id,
+                         ProjectLock.owner == owner)
+
+    # If there is already lock existing for the process, do not recreate. This
+    # helps the process continue with the project it was handling before it was
+    # killed.
+    if not query.all():
+        create_project_lock(project_id, owner)
+
+
+def delete_project_lock(project_id):
+    """Deletes project lock record.
+
+    This method has to work without SQLAlchemy session because session may not
+    immediately issue an SQL query to a database and instead just schedule it
+    whereas we need to make sure to issue a operation immediately.
+    """
+    session = get_session()
+    session.flush()
+
+    table = ProjectLock.__table__
+    delete = table.delete()
+    session.execute(delete.where(table.c.project_id == project_id))
+
+    session.flush()
+
+
+@contextlib.contextmanager
+def project_lock(project_id, owner):
+    try:
+        ensure_project_lock(project_id, owner)
+        yield
+    finally:
+        delete_project_lock(project_id)
diff --git a/distil/db/sqlalchemy/models.py b/distil/db/sqlalchemy/models.py
index f59932f..b6466af 100644
--- a/distil/db/sqlalchemy/models.py
+++ b/distil/db/sqlalchemy/models.py
@@ -119,3 +119,11 @@ class SalesOrder(DistilBase):
     @hybrid_method
     def intersects(self, other):
         return (self.start <= other.end and other.start <= self.end)
+
+
+class ProjectLock(DistilBase):
+    __tablename__ = 'project_locks'
+
+    project_id = Column(String(100), primary_key=True, nullable=False)
+    owner = Column(String(100), nullable=False)
+    created = Column(DateTime, nullable=False)
diff --git a/distil/service/collector.py b/distil/service/collector.py
index 4289cd8..d796a01 100644
--- a/distil/service/collector.py
+++ b/distil/service/collector.py
@@ -22,6 +22,7 @@ from stevedore import driver
 
 from distil.db import api as db_api
 from distil import exceptions
+from distil.common import general
 from distil.common import openstack
 
 LOG = logging.getLogger(__name__)
@@ -53,6 +54,8 @@ class CollectorService(service.Service):
 
         self.validate_config()
 
+        self.identifier = general.get_process_identifier()
+
         collector_args = {}
         self.collector = driver.DriverManager(
             'distil.collector',
@@ -93,15 +96,36 @@ class CollectorService(service.Service):
         logging.setup(CONF, 'distil-collector')
 
     def collect_usage(self):
-        LOG.info("Begin to collect usage for all projects...")
+        LOG.info("Starting to collect usage...")
 
         projects = filter_projects(openstack.get_projects())
 
         end = datetime.utcnow().replace(minute=0, second=0, microsecond=0)
+        count = 0
 
         for project in projects:
-            # Add a project or get last_collected of existing project.
-            db_project = db_api.project_add(project)
-            start = db_project.last_collected
+            # Check if the project is being processed by other collector
+            # instance. If no, will get a lock and continue processing,
+            # otherwise just skip it.
+            locks = db_api.get_project_locks(project['id'])
 
-            self.collector.collect_usage(project, start, end)
+            if locks and locks[0].owner != self.identifier:
+                LOG.debug(
+                    "Project %s is being processed by collector %s." %
+                    (project['id'], locks[0].owner)
+                )
+                continue
+
+            try:
+                with db_api.project_lock(project['id'], self.identifier):
+                    # Add a project or get last_collected of existing project.
+                    db_project = db_api.project_add(project)
+                    start = db_project.last_collected
+
+                    self.collector.collect_usage(project, start, end)
+
+                    count = count + 1
+            except Exception:
+                LOG.warning('Get lock failed. Process: %s' % self.identifier)
+
+        LOG.info("Finished collecting usage for %s projects." % count)
diff --git a/distil/tests/unit/base.py b/distil/tests/unit/base.py
index bfad63b..3186483 100644
--- a/distil/tests/unit/base.py
+++ b/distil/tests/unit/base.py
@@ -22,6 +22,7 @@ from oslo_log import log
 
 from distil import context
 from distil import config
+from distil.db import api as db_api
 
 class DistilTestCase(base.BaseTestCase):
 
@@ -34,7 +35,7 @@ class DistilTestCase(base.BaseTestCase):
         if self.config_file:
             self.conf = self.load_conf(self.config_file)
         else:
-            self.conf = cfg.ConfigOpts()
+            self.conf = cfg.CONF
 
         self.conf.register_opts(config.DEFAULT_OPTIONS)
         self.conf.register_opts(config.ODOO_OPTS, group=config.ODOO_GROUP)
@@ -72,12 +73,12 @@ class DistilTestCase(base.BaseTestCase):
 
         :returns: Project's config object.
         """
-        conf = cfg.ConfigOpts()
+        conf = cfg.CONF
         log.register_options(conf)
         conf(args=[], default_config_files=[cls.conf_path(filename)])
         return conf
 
-    def config(self, group=None, **kw):
+    def override_config(self, group=None, **kw):
         """Override some configuration values.
 
         The keyword arguments are the names of configuration options to
@@ -100,6 +101,6 @@ class DistilWithDbTestCase(DistilTestCase):
     def setUp(self):
         super(DistilWithDbTestCase, self).setUp()
 
-        self.override_config('connection', "sqlite://", group='database')
+        self.conf.set_default('connection', 'sqlite://', group='database')
         db_api.setup_db()
         self.addCleanup(db_api.drop_db)
diff --git a/distil/tests/unit/db/__init__.py b/distil/tests/unit/db/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/distil/tests/unit/db/test_sqlalchemy_db_api.py b/distil/tests/unit/db/test_sqlalchemy_db_api.py
new file mode 100644
index 0000000..7a74eae
--- /dev/null
+++ b/distil/tests/unit/db/test_sqlalchemy_db_api.py
@@ -0,0 +1,29 @@
+# Copyright (C) 2017 Catalyst IT Ltd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from distil.db.sqlalchemy import api as db_api
+from distil.tests.unit import base
+
+
+class ProjectLockTest(base.DistilWithDbTestCase):
+    def test_with_project_lock(self):
+        project_id = 'fake_project_id'
+        owner = 'fake_owner'
+
+        with db_api.project_lock(project_id, owner):
+            # Make sure that within 'with' section the lock record exists.
+            self.assertEqual(1, len(db_api.get_project_locks(project_id)))
+
+        # Make sure that outside 'with' section the lock record does not exist.
+        self.assertEqual(0, len(db_api.get_project_locks(project_id)))
diff --git a/requirements.txt b/requirements.txt
index d17e939..e1e40ea 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,6 +11,7 @@ odoorpc==0.4.2
 SQLAlchemy<1.1.0,>=1.0.10 # MIT
 keystonemiddleware!=4.1.0,>=4.0.0 # Apache-2.0
 keystoneauth1>=2.1.0  # Apache-2.0
+retrying>=1.2.3,!=1.3.0 # Apache-2.0
 
 python-cinderclient>=1.6.0 # Apache-2.0
 python-keystoneclient!=1.8.0,!=2.1.0,>=1.6.0 # Apache-2.0
diff --git a/tox.ini b/tox.ini
index 30a2741..28df0d5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -11,10 +11,14 @@ setenv =
     DISTIL_TESTS_CONFIGS_DIR={toxinidir}/distil/tests/etc/
     DISCOVER_DIRECTORY=distil/tests/unit
 deps =
-    -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args="{posargs}"
-whitelist_externals = bash
+commands =
+    find . -type f -name "*.pyc" -delete
+    python setup.py testr --slowest --testr-args="{posargs}"
+whitelist_externals =
+    bash
+    rm
+    find
 
 [testenv:py33]
 deps = -r{toxinidir}/requirements-py3.txt