diff --git a/requirements-nover.txt b/requirements-nover.txt
index 0ebe5534d..e55df79f7 100644
--- a/requirements-nover.txt
+++ b/requirements-nover.txt
@@ -56,3 +56,4 @@ toposort
 rfc3987
 pyjwkest
 jsonpath-rw
+bintrees
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
index a6f4c28a3..1fe1e4248 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,6 +4,7 @@ APScheduler==3.0.3
 autobahn==0.9.3-3
 Babel==1.3
 beautifulsoup4==4.4.0
+bintrees==2.0.2
 blinker==1.3
 boto==2.38.0
 cachetools==1.0.3
diff --git a/test/test_backfill_allocator.py b/test/test_backfill_allocator.py
new file mode 100644
index 000000000..40000cdb5
--- /dev/null
+++ b/test/test_backfill_allocator.py
@@ -0,0 +1,132 @@
+import unittest
+import logging
+import random
+
+from datetime import datetime, timedelta
+from util.migrate.allocator import CompletedKeys, NoAvailableKeysError
+
+
+class CompletedTestCase(unittest.TestCase):
+  def test_merge_blocks_operations(self):
+    candidates = CompletedKeys(10)
+    candidates.mark_completed(1, 5)
+
+    self.assertTrue(candidates.is_available(5))
+    self.assertTrue(candidates.is_available(0))
+    self.assertFalse(candidates.is_available(1))
+    self.assertFalse(candidates.is_available(4))
+    self.assertFalse(candidates.is_available(11))
+    self.assertFalse(candidates.is_available(10))
+    self.assertEqual(1, len(candidates._slabs))
+
+    candidates.mark_completed(5, 6)
+    self.assertFalse(candidates.is_available(5))
+    self.assertTrue(candidates.is_available(6))
+    self.assertEqual(1, len(candidates._slabs))
+
+    candidates.mark_completed(3, 8)
+    self.assertTrue(candidates.is_available(9))
+    self.assertTrue(candidates.is_available(8))
+    self.assertFalse(candidates.is_available(7))
+    self.assertEqual(1, len(candidates._slabs))
+
+  def test_adjust_max(self):
+    candidates = CompletedKeys(10)
+    self.assertEqual(0, len(candidates._slabs))
+
+    self.assertTrue(candidates.is_available(9))
+    candidates.mark_completed(5, 12)
+    self.assertEqual(0, len(candidates._slabs))
+
+    self.assertFalse(candidates.is_available(9))
+    self.assertTrue(candidates.is_available(4))
+
+  def test_adjust_min(self):
+    candidates = CompletedKeys(10)
+    self.assertEqual(0, len(candidates._slabs))
+
+    self.assertTrue(candidates.is_available(2))
+    candidates.mark_completed(0, 3)
+    self.assertEqual(0, len(candidates._slabs))
+
+    self.assertFalse(candidates.is_available(2))
+    self.assertTrue(candidates.is_available(4))
+
+  def test_inside_block(self):
+    candidates = CompletedKeys(10)
+    candidates.mark_completed(1, 8)
+    self.assertEqual(1, len(candidates._slabs))
+
+    candidates.mark_completed(2, 5)
+    self.assertEqual(1, len(candidates._slabs))
+    self.assertFalse(candidates.is_available(1))
+    self.assertFalse(candidates.is_available(5))
+
+  def test_wrap_block(self):
+    candidates = CompletedKeys(10)
+    candidates.mark_completed(2, 5)
+    self.assertEqual(1, len(candidates._slabs))
+
+    candidates.mark_completed(1, 8)
+    self.assertEqual(1, len(candidates._slabs))
+    self.assertFalse(candidates.is_available(1))
+    self.assertFalse(candidates.is_available(5))
+
+  def test_non_contiguous(self):
+    candidates = CompletedKeys(10)
+
+    candidates.mark_completed(1, 5)
+    self.assertEqual(1, len(candidates._slabs))
+    self.assertTrue(candidates.is_available(5))
+    self.assertTrue(candidates.is_available(6))
+
+    candidates.mark_completed(6, 8)
+    self.assertEqual(2, len(candidates._slabs))
+    self.assertTrue(candidates.is_available(5))
+    self.assertFalse(candidates.is_available(6))
+
+  def test_big_merge(self):
+    candidates = CompletedKeys(10)
+
+    candidates.mark_completed(1, 5)
+    self.assertEqual(1, len(candidates._slabs))
+
+    candidates.mark_completed(6, 8)
+    self.assertEqual(2, len(candidates._slabs))
+
+    candidates.mark_completed(5, 6)
+    self.assertEqual(1, len(candidates._slabs))
+
+  def test_range_limits(self):
+    candidates = CompletedKeys(10)
+    self.assertFalse(candidates.is_available(-1))
+    self.assertFalse(candidates.is_available(10))
+
+    self.assertTrue(candidates.is_available(9))
+    self.assertTrue(candidates.is_available(0))
+
+  def test_random_saturation(self):
+    candidates = CompletedKeys(100)
+    with self.assertRaises(NoAvailableKeysError):
+      for _ in range(101):
+        start = candidates.get_block_start_index(10)
+        self.assertTrue(candidates.is_available(start))
+        candidates.mark_completed(start, start + 10)
+
+  def test_huge_dataset(self):
+    candidates = CompletedKeys(1024 * 1024)
+    start_time = datetime.now()
+    iterations = 0
+    with self.assertRaises(NoAvailableKeysError):
+      while (datetime.now() - start_time) < timedelta(seconds=10):
+        start = candidates.get_block_start_index(1024)
+        self.assertTrue(candidates.is_available(start))
+        candidates.mark_completed(start, start + random.randint(512, 1024))
+        iterations += 1
+
+    self.assertGreater(iterations, 1024)
+
+
+if __name__ == '__main__':
+  logging.basicConfig(level=logging.DEBUG)
+  unittest.main()
diff --git a/util/migrate/__init__.py b/util/migrate/__init__.py
index e1770742d..809bcaef8 100644
--- a/util/migrate/__init__.py
+++ b/util/migrate/__init__.py
@@ -2,7 +2,6 @@ import logging
 
 from sqlalchemy.types import TypeDecorator, Text
 from sqlalchemy.dialects.mysql import TEXT as MySQLText, LONGTEXT
-from random import shuffle
 
 
 logger = logging.getLogger(__name__)
@@ -21,56 +20,3 @@ class UTF8LongText(TypeDecorator):
       return dialect.type_descriptor(LONGTEXT(charset='utf8mb4', collation='utf8mb4_unicode_ci'))
     else:
       return dialect.type_descriptor(Text())
-
-
-def _chance_duplication(pop_size, samples):
-  """ The chance of randomly selecting a duplicate when you choose the specified number of samples
-      from the specified population size.
-  """
-  pairs = (samples * (samples - 1)) / 2.0
-  unique = (pop_size - 1.0)/pop_size
-  all_unique = pow(unique, pairs)
-  return 1 - all_unique
-
-
-def _num_checks(pop_size, desired):
-  """ Binary search for the proper number of entries to use to get the specified collision
-      probability.
-  """
-  s_max = pop_size
-  s_min = 0
-  last_test = -1
-  s_test = s_max
-
-  while s_max > s_min and last_test != s_test:
-    last_test = s_test
-    s_test = (s_max + s_min)/2
-    chance = _chance_duplication(pop_size, s_test)
-    if chance > desired:
-      s_max = s_test - 1
-    else:
-      s_min = s_test
-
-  return s_test
-
-
-def yield_random_entries(batch_query, batch_size, collision_chance):
-  """ This method will yield semi-random items from a query in a database friendly way until no
-      more items match the base query modifier. It will pull batches of batch_size from the query
-      and yield enough items from each batch so that concurrent workers have a reduced chance of
-      selecting the same items. For example, if your batches return 10,000 entries, and you desire
-      only a .03 collision_chance, we will only use 25 random entries before going back to the db
-      for a new batch.
-  """
-
-  # Seed with some data which will pass the condition, but will be immediately discarded
-  all_candidates = [1]
-  while len(all_candidates) > 0:
-    all_candidates = list(batch_query().limit(batch_size))
-    shuffle(all_candidates)
-    num_selections = max(1, _num_checks(len(all_candidates), collision_chance))
-    logger.debug('Found %s/%s matching entries, processing %s', len(all_candidates), batch_size,
-                 num_selections)
-    candidates = all_candidates[0:num_selections]
-    for candidate in candidates:
-      yield candidate
diff --git a/util/migrate/allocator.py b/util/migrate/allocator.py
new file mode 100644
index 000000000..999416ace
--- /dev/null
+++ b/util/migrate/allocator.py
@@ -0,0 +1,156 @@
+import logging
+import random
+
+from bintrees import RBTree
+from threading import Event
+
+
+logger = logging.getLogger(__name__)
+logger.setLevel(logging.INFO)
+
+
+class NoAvailableKeysError(ValueError):
+  pass
+
+
+class CompletedKeys(object):
+  def __init__(self, max_index):
+    self._max_index = max_index
+    self._min_index = 0
+    self._slabs = RBTree()
+
+  def _get_previous_or_none(self, index):
+    try:
+      return self._slabs.floor_item(index)
+    except KeyError:
+      return None
+
+  def is_available(self, index):
+    logger.debug('Testing index %s', index)
+    if index >= self._max_index or index < self._min_index:
+      logger.debug('Index out of range')
+      return False
+
+    try:
+      prev_start, prev_length = self._slabs.floor_item(index)
+      logger.debug('Prev range: %s-%s', prev_start, prev_start + prev_length)
+      return (prev_start + prev_length) <= index
+    except KeyError:
+      return True
+
+  def mark_completed(self, start_index, past_last_index):
+    logger.debug('Marking the range completed: %s-%s', start_index, past_last_index)
+    # Find the item directly before this and see if there is overlap
+    to_discard = set()
+    try:
+      prev_start, prev_length = self._slabs.floor_item(start_index)
+      if prev_start + prev_length >= start_index:
+        # we are going to merge with the range before us
+        logger.debug('Merging with the prev range: %s-%s', prev_start, prev_start + prev_length)
+        to_discard.add(prev_start)
+        start_index = prev_start
+        past_last_index = max(past_last_index, prev_start + prev_length)
+    except KeyError:
+      pass
+
+    # Find all keys between the start and last index and merge them into one block
+    for merge_start, merge_length in self._slabs.iter_items(start_index, past_last_index + 1):
+      candidate_next_index = merge_start + merge_length
+      logger.debug('Merging with block %s-%s', merge_start, candidate_next_index)
+      to_discard.add(merge_start)
+      past_last_index = max(past_last_index, candidate_next_index)
+
+    # write the new block which is fully merged
+    discard = False
+    if past_last_index >= self._max_index:
+      logger.debug('Discarding block and setting new max to: %s', start_index)
+      self._max_index = start_index
+      discard = True
+
+    if start_index <= self._min_index:
+      logger.debug('Discarding block and setting new min to: %s', past_last_index)
+      self._min_index = past_last_index
+      discard = True
+
+    if to_discard:
+      logger.debug('Discarding %s obsolte blocks', len(to_discard))
+      self._slabs.remove_items(to_discard)
+
+    if not discard:
+      logger.debug('Writing new block with range: %s-%s', start_index, past_last_index)
+      self._slabs.insert(start_index, past_last_index - start_index)
+
+    logger.debug('Total blocks: %s', len(self._slabs))
+
+  def get_block_start_index(self, block_size_estimate):
+    logger.debug('Total range: %s-%s', self._min_index, self._max_index)
+    if self._max_index <= self._min_index:
+      raise NoAvailableKeysError('All indexes have been marked completed')
+
+    num_holes = len(self._slabs) + 1
+    random_hole = random.randint(0, num_holes - 1)
+    logger.debug('Selected random hole %s with %s total holes', random_hole, num_holes)
+
+    hole_start = self._min_index
+    past_hole_end = self._max_index
+
+    # Now that we have picked a hole, we need to define the bounds
+    if random_hole > 0:
+      # There will be a slab before this hole, find where it ends
+      bound_entries = self._slabs.nsmallest(random_hole + 1)[-2:]
+      left_index, left_len = bound_entries[0]
+      logger.debug('Left range %s-%s', left_index, left_index + left_len)
+      hole_start = left_index + left_len
+
+      if len(bound_entries) > 1:
+        right_index, right_len = bound_entries[1]
+        logger.debug('Right range %s-%s', right_index, right_index + right_len)
+        past_hole_end, _ = bound_entries[1]
+    elif not self._slabs.is_empty():
+      right_index, right_len = self._slabs.nsmallest(1)[0]
+      logger.debug('Right range %s-%s', right_index, right_index + right_len)
+      past_hole_end, _ = self._slabs.nsmallest(1)[0]
+
+    # Now that we have our hole bounds, select a random block from [0:len - block_size_estimate]
+    logger.debug('Selecting from hole range: %s-%s', hole_start, past_hole_end)
+    rand_max_bound = max(hole_start, past_hole_end - block_size_estimate)
+    logger.debug('Rand max bound: %s', rand_max_bound)
+    return random.randint(hole_start, rand_max_bound)
+
+
+def yield_random_entries(batch_query, primary_key_field, batch_size, max_id):
+  """ This method will yield items from random blocks in the database. We will track metadata
+      about which keys are available for work, and we will complete the backfill when there is no
+      more work to be done. The method yields tupes of (candidate, Event), and if the work was
+      already done by another worker, the caller should set the event. Batch candidates must have
+      an "id" field which can be inspected.
+  """
+
+  allocator = CompletedKeys(max_id + 1)
+
+  try:
+    while True:
+      start_index = allocator.get_block_start_index(batch_size)
+      all_candidates = list(batch_query()
+                            .limit(batch_size)
+                            .where(primary_key_field >= start_index))
+
+      if len(all_candidates) == 0:
+        logger.debug('No candidates, new highest id: %s', start_index)
+        allocator.mark_completed(start_index, max_id)
+        continue
+
+      logger.debug('Found %s candidates, processing block')
+      for candidate in all_candidates:
+        abort_early = Event()
+        yield candidate, abort_early
+        if abort_early.is_set():
+          logger.debug('Overlap with another worker, aborting')
+          break
+
+      completed_through = candidate.id + 1
+      logger.debug('Marking id range as completed: %s-%s', start_index, completed_through)
+      allocator.mark_completed(start_index, completed_through)
+
+  except NoAvailableKeysError:
+    logger.debug('No more work')
diff --git a/util/migrate/backfill_content_checksums.py b/util/migrate/backfill_content_checksums.py
index 645b5539e..86770a35b 100644
--- a/util/migrate/backfill_content_checksums.py
+++ b/util/migrate/backfill_content_checksums.py
@@ -3,12 +3,12 @@ import logging
 from peewee import JOIN_LEFT_OUTER
 
 from peewee import (CharField, BigIntegerField, BooleanField, ForeignKeyField, DateTimeField,
-                    TextField)
+                    TextField, fn)
 
 from data.database import BaseModel, db, db_for_update, CloseForLongOperation
 from app import app, storage
 from digest import checksums
-from util.migrate import yield_random_entries
+from util.migrate.allocator import yield_random_entries
 
 
 logger = logging.getLogger(__name__)
@@ -76,7 +76,9 @@ def backfill_content_checksums():
             .select(ImageStorage.id, ImageStorage.uuid)
             .where(ImageStorage.content_checksum >> None, ImageStorage.uploading == False))
 
-  for candidate_storage in yield_random_entries(batch_query, 10000, 0.1):
+  max_id = ImageStorage.select(fn.Max(ImageStorage.id)).scalar()
+
+  for candidate_storage, abort in yield_random_entries(batch_query, ImageStorage.id, 1000, max_id):
     logger.debug('Computing content checksum for storage: %s', candidate_storage.uuid)
 
     locations = _get_image_storage_locations(candidate_storage.id)
@@ -97,12 +99,13 @@ def backfill_content_checksums():
       to_update = db_for_update(ImageStorage.get(ImageStorage.id == candidate_storage.id))
       if to_update.content_checksum is not None:
         logger.info('Another worker filled in the checksum: %s', candidate_storage.uuid)
+        abort.set()
       else:
         logger.debug('Setting content checksum to %s for %s', checksum, candidate_storage.uuid)
         to_update.content_checksum = checksum
         to_update.save()
 
-if __name__ == "__main__":
+if __name__ == '__main__':
   logging.basicConfig(level=logging.DEBUG)
   # logging.getLogger('peewee').setLevel(logging.CRITICAL)
   backfill_content_checksums()
diff --git a/util/migrate/backfill_parent_id.py b/util/migrate/backfill_parent_id.py
index 1d2cf4136..fc2db3bff 100644
--- a/util/migrate/backfill_parent_id.py
+++ b/util/migrate/backfill_parent_id.py
@@ -1,8 +1,41 @@
 import logging
 
-from data.database import Image, ImageStorage, db, db_for_update
+from data.database import BaseModel, db, db_for_update
+from peewee import (fn, CharField, BigIntegerField, ForeignKeyField, BooleanField, DateTimeField,
+                    TextField, IntegerField)
 from app import app
-from util.migrate import yield_random_entries
+from util.migrate.allocator import yield_random_entries
+
+class Repository(BaseModel):
+  pass
+
+
+# Vendor the information from tables we will be writing to at the time of this migration
+class ImageStorage(BaseModel):
+  uuid = CharField(index=True, unique=True)
+  checksum = CharField(null=True)
+  image_size = BigIntegerField(null=True)
+  uncompressed_size = BigIntegerField(null=True)
+  uploading = BooleanField(default=True, null=True)
+  cas_path = BooleanField(default=True)
+  content_checksum = CharField(null=True, index=True)
+
+
+class Image(BaseModel):
+  docker_image_id = CharField(index=True)
+  repository = ForeignKeyField(Repository)
+  ancestors = CharField(index=True, default='/', max_length=64535, null=True)
+  storage = ForeignKeyField(ImageStorage, index=True, null=True)
+  created = DateTimeField(null=True)
+  comment = TextField(null=True)
+  command = TextField(null=True)
+  aggregate_size = BigIntegerField(null=True)
+  v1_json_metadata = TextField(null=True)
+  v1_checksum = CharField(null=True)
+
+  security_indexed = BooleanField(default=False)
+  security_indexed_engine = IntegerField(default=-1)
+  parent_id = IntegerField(index=True, null=True)
 
 
 logger = logging.getLogger(__name__)
@@ -21,20 +54,23 @@ def backfill_parent_id():
             .where(Image.parent_id >> None, Image.ancestors != '/',
                    ImageStorage.uploading == False))
 
-  for to_backfill in yield_random_entries(fetch_batch, 10000, 0.3):
+  max_id = Image.select(fn.Max(Image.id)).scalar()
+
+  for to_backfill, abort in yield_random_entries(fetch_batch, Image.id, 1000, max_id):
     with app.config['DB_TRANSACTION_FACTORY'](db):
       try:
         image = db_for_update(Image
                               .select()
-                              .where(Image.id == to_backfill.id)).get()
+                              .where(Image.id == to_backfill.id, Image.parent_id >> None)).get()
         image.parent_id = int(to_backfill.ancestors.split('/')[-2])
         image.save()
       except Image.DoesNotExist:
-        pass
+        logger.info('Collision with another worker, aborting batch')
+        abort.set()
 
   logger.debug('backfill_parent_id: Completed')
 
-if __name__ == "__main__":
+if __name__ == '__main__':
   logging.basicConfig(level=logging.DEBUG)
   logging.getLogger('peewee').setLevel(logging.CRITICAL)
 
diff --git a/util/migrate/backfill_v1_checksums.py b/util/migrate/backfill_v1_checksums.py
index aef7af72e..e9516cf91 100644
--- a/util/migrate/backfill_v1_checksums.py
+++ b/util/migrate/backfill_v1_checksums.py
@@ -1,9 +1,9 @@
 import logging
 
 from peewee import (CharField, BigIntegerField, BooleanField, ForeignKeyField, DateTimeField,
-                    TextField)
+                    TextField, fn)
 from data.database import BaseModel, db, db_for_update
-from util.migrate import yield_random_entries
+from util.migrate.allocator import yield_random_entries
 from app import app
 
 
@@ -48,20 +48,22 @@ def backfill_checksums():
             .where(Image.v1_checksum >> None, ImageStorage.uploading == False,
                    ~(ImageStorage.checksum >> None)))
 
-  for candidate_image in yield_random_entries(batch_query, 10000, 0.1):
-    logger.debug('Computing content checksum for storage: %s', candidate_image.id)
+  max_id = Image.select(fn.Max(Image.id)).scalar()
 
+  for candidate_image, abort in yield_random_entries(batch_query, Image.id, 1000, max_id):
     with app.config['DB_TRANSACTION_FACTORY'](db):
       try:
         image = db_for_update(Image
                               .select(Image, ImageStorage)
                               .join(ImageStorage)
-                              .where(Image.id == candidate_image.id)).get()
+                              .where(Image.id == candidate_image.id,
+                                     Image.v1_checksum >> None)).get()
 
         image.v1_checksum = image.storage.checksum
         image.save()
       except Image.DoesNotExist:
-        pass
+        logger.info('Collision with another worker, aborting batch')
+        abort.set()
 
 
 if __name__ == "__main__":