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(minor improvement): small refactoring in make_token_replica_map() #513

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Merged
merged 2 commits into from
Aug 11, 2025
Merged

(minor improvement): small refactoring in make_token_replica_map() #513

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40ed630
(minor improvement): small refactoring in NetworkTopologyStrategy's m…
mykaul Aug 7, 2025
b9e5d44
(minor improvement): small refactoring in SimpleStrategy's make_token…
mykaul Aug 11, 2025
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43 changes: 23 additions & 20 deletions cassandra/metadata.py
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Original file line number Diff line number Diff line change
Expand Up @@ -569,10 +569,11 @@ def __init__(self, options_map):

def make_token_replica_map(self, token_to_host_owner, ring):
replica_map = {}
for i in range(len(ring)):
ring_len = len(ring)
for i in range(ring_len):
j, hosts = 0, list()
while len(hosts) < self.replication_factor and j < len(ring):
token = ring[(i + j) % len(ring)]
while len(hosts) < self.replication_factor and j < ring_len:
token = ring[(i + j) % ring_len]
host = token_to_host_owner[token]
if host not in hosts:
hosts.append(host)
Expand Down Expand Up @@ -629,10 +630,14 @@ def make_token_replica_map(self, token_to_host_owner, ring):
hosts_per_dc = defaultdict(set)
for i, token in enumerate(ring):
host = token_to_host_owner[token]
dc_to_token_offset[host.datacenter].append(i)
if host.datacenter and host.rack:
dc_racks[host.datacenter].add(host.rack)
hosts_per_dc[host.datacenter].add(host)
host_dc = host.datacenter
if host_dc in dc_rf_map:
# if the host is in a DC that has a replication factor, add it
# to the list of token offsets for that DC
dc_to_token_offset[host_dc].append(i)
if host.rack:
dc_racks[host_dc].add(host.rack)
hosts_per_dc[host_dc].add(host)

# A map of DCs to an index into the dc_to_token_offset value for that dc.
# This is how we keep track of advancing around the ring for each DC.
Expand All @@ -644,8 +649,6 @@ def make_token_replica_map(self, token_to_host_owner, ring):

# go through each DC and find the replicas in that DC
for dc in dc_to_token_offset.keys():
if dc not in dc_rf_map:
continue

# advance our per-DC index until we're up to at least the
# current token in the ring
Expand All @@ -657,34 +660,34 @@ def make_token_replica_map(self, token_to_host_owner, ring):
dc_to_current_index[dc] = index

replicas_remaining = dc_rf_map[dc]
replicas_this_dc = 0
num_replicas_this_dc = 0
skipped_hosts = []
racks_placed = set()
racks_this_dc = dc_racks[dc]
hosts_this_dc = len(hosts_per_dc[dc])
num_racks_this_dc = len(dc_racks[dc])
num_hosts_this_dc = len(hosts_per_dc[dc])

for token_offset_index in range(index, index+num_tokens):
if token_offset_index >= len(token_offsets):
token_offset_index = token_offset_index - len(token_offsets)
if replicas_remaining == 0 or num_replicas_this_dc == num_hosts_this_dc:
break

if token_offset_index >= num_tokens:
token_offset_index = token_offset_index - num_tokens

token_offset = token_offsets[token_offset_index]
host = token_to_host_owner[ring[token_offset]]
if replicas_remaining == 0 or replicas_this_dc == hosts_this_dc:
break

if host in replicas:
continue

if host.rack in racks_placed and len(racks_placed) < len(racks_this_dc):
if host.rack in racks_placed and len(racks_placed) < num_racks_this_dc:
skipped_hosts.append(host)
continue

replicas.append(host)
replicas_this_dc += 1
num_replicas_this_dc += 1
replicas_remaining -= 1
racks_placed.add(host.rack)

if len(racks_placed) == len(racks_this_dc):
if len(racks_placed) == num_racks_this_dc:
for host in skipped_hosts:
if replicas_remaining == 0:
break
Expand Down
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