Skip to content

Fix TokenAwarePolicy to call child.make_query_plan once #634

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
Copilot wants to merge 5 commits into
base: master
Choose a base branch
from
+81 −22
Draft

Fix TokenAwarePolicy to call child.make_query_plan once #634

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
3481055
Initial plan
Copilot Dec 27, 2025
507b252
Optimize TokenAwarePolicy to call child.make_query_plan only once
Copilot Dec 29, 2025
ec8203e
Address code review: optimize memory usage for early return case
Copilot Jan 3, 2026
85c6ee8
Improve code comments for clarity on memory optimization
Copilot Jan 3, 2026
d49f4dd
Refactor: simplify tablet check by removing redundant table_has_table…
Copilot Jan 20, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 14 additions & 8 deletions cassandra/policies.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -505,21 +505,27 @@ def make_query_plan(self, working_keyspace=None, query=None):
keyspace = query.keyspace if query and query.keyspace else working_keyspace

child = self._child_policy

# Early return case: pass through the generator to preserve lazy evaluation
# This avoids materializing the full host list in memory when we don't need token-aware routing
if query is None or query.routing_key is None or keyspace is None:
for host in child.make_query_plan(keyspace, query):
yield host
return

# Call child.make_query_plan only once and convert to list for reuse
# List conversion is necessary because we iterate over it twice:
# 1. To identify replicas (either from tablets or token ring)
# 2. To yield remaining hosts not in the replica set
child_plan = list(child.make_query_plan(keyspace, query))

replicas = []
if self._cluster_metadata._tablets.table_has_tablets(keyspace, query.table):
tablet = self._cluster_metadata._tablets.get_tablet_for_key(
tablet = self._cluster_metadata._tablets.get_tablet_for_key(
keyspace, query.table, self._cluster_metadata.token_map.token_class.from_key(query.routing_key))

if tablet is not None:
replicas_mapped = set(map(lambda r: r[0], tablet.replicas))
child_plan = child.make_query_plan(keyspace, query)

replicas = [host for host in child_plan if host.host_id in replicas_mapped]
if tablet is not None:
replicas_mapped = set(map(lambda r: r[0], tablet.replicas))
replicas = [host for host in child_plan if host.host_id in replicas_mapped]
else:
replicas = self._cluster_metadata.get_replicas(keyspace, query.routing_key)

Expand All @@ -535,7 +541,7 @@ def yield_in_order(hosts):
# yield replicas: local_rack, local, remote
yield from yield_in_order(replicas)
# yield rest of the cluster: local_rack, local, remote
yield from yield_in_order([host for host in child.make_query_plan(keyspace, query) if host not in replicas])
yield from yield_in_order([host for host in child_plan if host not in replicas])

def on_up(self, *args, **kwargs):
return self._child_policy.on_up(*args, **kwargs)
Expand Down
81 changes: 67 additions & 14 deletions tests/unit/test_policies.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -584,7 +584,7 @@ def test_wrap_round_robin(self):
cluster = Mock(spec=Cluster)
cluster.metadata = Mock(spec=Metadata)
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata._tablets.table_has_tablets.return_value = []
cluster.metadata._tablets.get_tablet_for_key.return_value = None
hosts = [Host(DefaultEndPoint(str(i)), SimpleConvictionPolicy) for i in range(4)]
for host in hosts:
host.set_up()
Expand Down Expand Up @@ -617,7 +617,7 @@ def test_wrap_dc_aware(self):
cluster = Mock(spec=Cluster)
cluster.metadata = Mock(spec=Metadata)
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata._tablets.table_has_tablets.return_value = []
cluster.metadata._tablets.get_tablet_for_key.return_value = None
hosts = [Host(DefaultEndPoint(str(i)), SimpleConvictionPolicy) for i in range(4)]
for host in hosts:
host.set_up()
Expand Down Expand Up @@ -666,7 +666,7 @@ def test_wrap_rack_aware(self):
cluster = Mock(spec=Cluster)
cluster.metadata = Mock(spec=Metadata)
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata._tablets.table_has_tablets.return_value = []
cluster.metadata._tablets.get_tablet_for_key.return_value = None
hosts = [Host(DefaultEndPoint(str(i)), SimpleConvictionPolicy) for i in range(8)]
for host in hosts:
host.set_up()
Expand Down Expand Up @@ -811,7 +811,7 @@ def test_statement_keyspace(self):
cluster.metadata._tablets = Mock(spec=Tablets)
replicas = hosts[2:]
cluster.metadata.get_replicas.return_value = replicas
cluster.metadata._tablets.table_has_tablets.return_value = []
cluster.metadata._tablets.get_tablet_for_key.return_value = None

child_policy = Mock()
child_policy.make_query_plan.return_value = hosts
Expand Down Expand Up @@ -904,7 +904,7 @@ def _prepare_cluster_with_vnodes(self):
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata.all_hosts.return_value = hosts
cluster.metadata.get_replicas.return_value = hosts[2:]
cluster.metadata._tablets.table_has_tablets.return_value = False
cluster.metadata._tablets.get_tablet_for_key.return_value = None
return cluster

def _prepare_cluster_with_tablets(self):
Expand All @@ -916,7 +916,6 @@ def _prepare_cluster_with_tablets(self):
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata.all_hosts.return_value = hosts
cluster.metadata.get_replicas.return_value = hosts[2:]
cluster.metadata._tablets.table_has_tablets.return_value = True
cluster.metadata._tablets.get_tablet_for_key.return_value = Tablet(replicas=[(h.host_id, 0) for h in hosts[2:]])
return cluster

Expand All @@ -931,8 +930,6 @@ def _assert_shuffle(self, patched_shuffle, cluster, keyspace, routing_key):
policy = TokenAwarePolicy(child_policy, shuffle_replicas=True)
policy.populate(cluster, hosts)

is_tablets = cluster.metadata._tablets.table_has_tablets()

cluster.metadata.get_replicas.reset_mock()
child_policy.make_query_plan.reset_mock()
query = Statement(routing_key=routing_key)
Expand All @@ -945,13 +942,69 @@ def _assert_shuffle(self, patched_shuffle, cluster, keyspace, routing_key):
else:
assert set(replicas) == set(qplan[:2])
assert hosts[:2] == qplan[2:]
if is_tablets:
child_policy.make_query_plan.assert_called_with(keyspace, query)
assert child_policy.make_query_plan.call_count == 2
else:
child_policy.make_query_plan.assert_called_once_with(keyspace, query)
# After optimization, child.make_query_plan should be called once for both tablets and vnodes
child_policy.make_query_plan.assert_called_once_with(keyspace, query)
assert patched_shuffle.call_count == 1

def test_child_make_query_plan_called_once(self):
"""
Test to validate that child.make_query_plan is called only once
in all scenarios (with/without tablets, with/without routing key)

@test_category policy
"""
# Test with vnodes (no tablets)
hosts = [Host(DefaultEndPoint(str(i)), SimpleConvictionPolicy) for i in range(4)]
for host in hosts:
host.set_up()

cluster = Mock(spec=Cluster)
cluster.metadata = Mock(spec=Metadata)
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata._tablets.get_tablet_for_key.return_value = None # No tablets for this table
replicas = hosts[2:]
cluster.metadata.get_replicas.return_value = replicas

child_policy = Mock()
child_policy.make_query_plan.return_value = hosts
child_policy.distance.return_value = HostDistance.LOCAL

policy = TokenAwarePolicy(child_policy)
policy.populate(cluster, hosts)

# Test case 1: With routing key and keyspace (should call once)
child_policy.reset_mock()
keyspace = 'keyspace'
routing_key = 'routing_key'
query = Statement(routing_key=routing_key, keyspace=keyspace)
qplan = list(policy.make_query_plan(keyspace, query))
child_policy.make_query_plan.assert_called_once_with(keyspace, query)

# Test case 2: Without routing key (should call once)
child_policy.reset_mock()
query = Statement(routing_key=None, keyspace=keyspace)
qplan = list(policy.make_query_plan(keyspace, query))
child_policy.make_query_plan.assert_called_once_with(keyspace, query)

# Test case 3: Without keyspace (should call once)
child_policy.reset_mock()
query = Statement(routing_key=routing_key, keyspace=None)
qplan = list(policy.make_query_plan(None, query))
child_policy.make_query_plan.assert_called_once_with(None, query)

# Test case 4: With tablets (should call once)
tablet = Mock(spec=Tablet)
tablet.replicas = [(hosts[0].host_id, None), (hosts[1].host_id, None)]
cluster.metadata._tablets.get_tablet_for_key.return_value = tablet
cluster.metadata.token_map = Mock()
cluster.metadata.token_map.token_class = Mock()
cluster.metadata.token_map.token_class.from_key.return_value = 'token'

child_policy.reset_mock()
query = Statement(routing_key=routing_key, keyspace=keyspace, table='test_table')
qplan = list(policy.make_query_plan(keyspace, query))
child_policy.make_query_plan.assert_called_once_with(keyspace, query)


class ConvictionPolicyTest(unittest.TestCase):
def test_not_implemented(self):
Expand Down Expand Up @@ -1638,7 +1691,7 @@ def get_replicas(keyspace, packed_key):

cluster.metadata.get_replicas.side_effect = get_replicas
cluster.metadata._tablets = Mock(spec=Tablets)
cluster.metadata._tablets.table_has_tablets.return_value = []
cluster.metadata._tablets.get_tablet_for_key.return_value = None

child_policy = TokenAwarePolicy(RoundRobinPolicy())

Expand Down