cassandra_tokens.py

#!/usr/bin/env python
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# 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 sys

if len(sys.argv) != 3:
  print "usage: cassandra_tokens.py <current_size> <new_size>"
  sys.exit(1)

CURRENT_NODES = int(sys.argv[1])
GOING_TO_NODES = int(sys.argv[2])

RING_SIZE = 2**127

def tokens(n):
  rv = []
  for x in xrange(n): 
    rv.append(RING_SIZE / n * x)
  return rv

def print_layout(nodes):
  i = 0
  for n in nodes:
    i += 1
    print "%d:\t%d" % (i, n)

current = tokens(CURRENT_NODES)
go = tokens(GOING_TO_NODES)
print "Existing Layout: "
print_layout(current)
print ""
print ""
print "New Layout: "
print_layout(go)

print ""
print ""
i = 0
j = 0
pending = []
while j != len(go) and i != len(current):
  cur = current[i]
  next = go[j]

  if next == cur:
    if pending:
      for x in pending:
        print x
      pending = []
    print "[%d] Old Node %d stays at %d" % (j+1, i+1, cur)
    i += 1

  if next > cur:
    if pending:
      for x in pending:
        print x
      pending = []
    #diff = (next - cur)
    print "[%d] Old Node %d moves to %d" % (j+1, i+1, next)
    i += 1

  if next < cur:
    pending.insert(0, "[%d] New Node added at %d" % (j+1, next))
  j += 1

if pending:
  for x in pending:
    print x
  pending = []

while j != len(go):
  print "[%d] Add new node %d at %d" % (j+1, j+1, go[j])
  j += 1