openstack/deb-python-cassandra-driver
Code Issues Proposed changes

Tolerate unknown host DCs more gracefully

Browse Source 
For load balancing purposes, hosts are assumed to be in
the local datacenter now if the actual datacenter is unknown.

However, this is still a slight problem with contact points
in a remote DC when using DCAwareRoundRobinPolicy. See
https://datastax-oss.atlassian.net/browse/JAVA-138 for
more details.

Fixes #5
This commit is contained in:
Tyler Hobbs
2013-07-30 11:05:13 -05:00
parent 2e7b42f84c
commit 0f1f81c932
1 changed files with 16 additions and 10 deletions
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26
cassandra/policies.py
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@@ -186,25 +186,31 @@ class DCAwareRoundRobinPolicy(LoadBalancingPolicy):
self.used_hosts_per_remote_dc = used_hosts_per_remote_dc self.used_hosts_per_remote_dc = used_hosts_per_remote_dc
self._dc_live_hosts = {} self._dc_live_hosts = {}
def _dc(self, host):
return host.datacenter or self.local_dc
def populate(self, cluster, hosts): def populate(self, cluster, hosts):
for dc, dc_hosts in groupby(hosts, lambda h: h.datacenter): for dc, dc_hosts in groupby(hosts, lambda h: self._dc(h)):
self._dc_live_hosts[dc] = set(dc_hosts) self._dc_live_hosts[dc] = set(dc_hosts)
# position is currently only used for local hosts # position is currently only used for local hosts
local_live = self._dc_live_hosts.get(self.local_dc) local_live = self._dc_live_hosts.get(self.local_dc)
if len(local_live) == 1: if not local_live:
self._position = 0
elif len(local_live) == 1:
self._position = 0 self._position = 0
else: else:
self._position = randint(0, len(local_live) - 1) self._position = randint(0, len(local_live) - 1)
def distance(self, host): def distance(self, host):
if host.datacenter == self.local_dc: dc = self._dc(host)
if dc == self.local_dc:
return HostDistance.LOCAL return HostDistance.LOCAL
if not self.used_hosts_per_remote_dc: if not self.used_hosts_per_remote_dc:
return HostDistance.IGNORED return HostDistance.IGNORED
else: else:
dc_hosts = self._dc_live_hosts.get(host.datacenter) dc_hosts = self._dc_live_hosts.get(dc)
if not dc_hosts: if not dc_hosts:
return HostDistance.IGNORED return HostDistance.IGNORED
@@ -219,8 +225,8 @@ class DCAwareRoundRobinPolicy(LoadBalancingPolicy):
pos = self._position pos = self._position
self._position += 1 self._position += 1
local_live = list(self._dc_live_hosts.get(self.local_dc)) local_live = list(self._dc_live_hosts.get(self.local_dc, ()))
pos %= len(local_live) pos = (pos % len(local_live)) if local_live else 0
for host in islice(cycle(local_live), pos, pos + len(local_live)): for host in islice(cycle(local_live), pos, pos + len(local_live)):
yield host yield host
@@ -232,16 +238,16 @@ class DCAwareRoundRobinPolicy(LoadBalancingPolicy):
yield host yield host
def on_up(self, host): def on_up(self, host):
self._dc_live_hosts.setdefault(host.datacenter, set()).add(host) self._dc_live_hosts.setdefault(self._dc(host), set()).add(host)
def on_down(self, host): def on_down(self, host):
self._dc_live_hosts.setdefault(host.datacenter, set()).discard(host) self._dc_live_hosts.setdefault(self._dc(host), set()).discard(host)
def on_add(self, host): def on_add(self, host):
self._dc_live_hosts.setdefault(host.datacenter, set()).add(host) self._dc_live_hosts.setdefault(self._dc(host), set()).add(host)
def on_remove(self, host): def on_remove(self, host):
self._dc_live_hosts.setdefault(host.datacenter, set()).discard(host) self._dc_live_hosts.setdefault(self._dc(host), set()).discard(host)
class TokenAwarePolicy(LoadBalancingPolicy): class TokenAwarePolicy(LoadBalancingPolicy):