(minor improvement): small refactoring in make_token_replica_map()

While trying to look at some random (flaky?) test (#510 (comment) )
I saw some (minor) improvements that can be made to make_token_replica_map():
1. Remove some redundant len() calls to outside the loop(s)
2. Align some variable names, start with num_ ... for them.
3. Move token_offset and host assignment within the loop to closer to where it's used.

All those are probably very very minor improvements, perhaps in a large cluster it'll be noticable.

Signed-off-by: Yaniv Kaul <[email protected]>

Author: mykaul

cassandra/metadata.py

@@ -657,34 +657,34 @@ 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 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:
+                    if replicas_remaining == 0 or num_replicas_this_dc == num_hosts_this_dc:
                         break
 
+                    token_offset = token_offsets[token_offset_index]
+                    host = token_to_host_owner[ring[token_offset]]
                     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