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policies: fix dc aware and rack aware policies initialization #578

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Merged
dkropachev merged 1 commit into from
Nov 4, 2025
Merged

policies: fix dc aware and rack aware policies initialization #578

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7 changes: 3 additions & 4 deletions cassandra/policies.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@
import random

from collections import namedtuple
from functools import lru_cache
from itertools import islice, cycle, groupby, repeat
import logging
from random import randint, shuffle
Expand Down Expand Up @@ -254,7 +253,7 @@ def _dc(self, host):

def populate(self, cluster, hosts):
for dc, dc_hosts in groupby(hosts, lambda h: self._dc(h)):
self._dc_live_hosts[dc] = tuple(set(dc_hosts))
self._dc_live_hosts[dc] = tuple({*dc_hosts, *self._dc_live_hosts.get(dc, [])})

Comment on lines 255 to 257
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@Lorak-mmk Lorak-mmk Nov 4, 2025

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Personally I think such comprehensions / unpacking (or w/e is this called) is much less readable than something simpler like

for dc, dc_hosts in groupby(hosts, lambda h: self._dc(h)):
    self._dc_live_hosts.setdefault(dc, set())
    self._dc_live_hosts[dc].update(dc_hosts)

I'd prefer it to be changed, but I won't hold this PR over that.

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@Lorak-mmk Lorak-mmk Nov 4, 2025

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Btw if we are staying with the current version, let's change .get(dc, []) to .get(dc,set()).
It won't change how the code works but makes it imo easier to reason about - _dc_live_hosts is a dict str -> set of hosts, so let's keep it that way.

if not self.local_dc:
self._endpoints = [
Expand Down Expand Up @@ -374,9 +373,9 @@ def _dc(self, host):

def populate(self, cluster, hosts):
for (dc, rack), rack_hosts in groupby(hosts, lambda host: (self._dc(host), self._rack(host))):
self._live_hosts[(dc, rack)] = tuple(set(rack_hosts))
self._live_hosts[(dc, rack)] = tuple({*rack_hosts, *self._live_hosts.get((dc, rack), [])})
for dc, dc_hosts in groupby(hosts, lambda host: self._dc(host)):
self._dc_live_hosts[dc] = tuple(set(dc_hosts))
self._dc_live_hosts[dc] = tuple({*dc_hosts, *self._dc_live_hosts.get(dc, [])})

self._position = randint(0, len(hosts) - 1) if hosts else 0

Expand Down
6 changes: 5 additions & 1 deletion tests/unit/test_policies.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@
# 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.

import random
import unittest

from itertools import islice, cycle
Expand Down Expand Up @@ -199,6 +199,8 @@ def test_no_remote(self, policy_specialization, constructor_args):
h.set_location_info("dc1", "rack1")
hosts.append(h)

random.shuffle(hosts)

policy = policy_specialization(*constructor_args)
policy.populate(None, hosts)
qplan = list(policy.make_query_plan())
Expand All @@ -213,6 +215,8 @@ def test_with_remotes(self, policy_specialization, constructor_args):
for h in hosts[4:]:
h.set_location_info("dc2", "rack1")

random.shuffle(hosts)

local_rack_hosts = set(h for h in hosts if h.datacenter == "dc1" and h.rack == "rack1")
local_hosts = set(h for h in hosts if h.datacenter == "dc1" and h.rack != "rack1")
remote_hosts = set(h for h in hosts if h.datacenter != "dc1")
Expand Down
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