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Fix hfp docs #802

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Merged
mambocab merged 2 commits into from
Jul 19, 2017
Merged

Fix hfp docs #802

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343c99e
fix HFP docs to account for new behavior
mambocab Jul 19, 2017
0a2efb4
make comment stop rendering
mambocab Jul 19, 2017
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17 changes: 13 additions & 4 deletions cassandra/policies.py
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Original file line number Diff line number Diff line change
Expand Up @@ -485,6 +485,10 @@ def address_is_ignored(host):
load_balancing_policy=blacklist_filter_policy,
)

See the note in the :meth:`.make_query_plan` documentation for a caveat on
how wrapping ordering polices (e.g. :class:`.RoundRobinPolicy`) may break
desirable properties of the wrapped policy.

Please note that whitelist and blacklist policies are not recommended for
general, day-to-day use. You probably want something like
:class:`.DCAwareRoundRobinPolicy`, which prefers a local DC but has
Expand Down Expand Up @@ -553,10 +557,15 @@ def populate(self, cluster, hosts):
def make_query_plan(self, working_keyspace=None, query=None):
"""
Defers to the child policy's
:meth:`.LoadBalancingPolicy.make_query_plan`. Since host changes (up,
down, addition, and removal) have not been propagated to the child
policy, the child policy will only ever return policies for which
:meth:`.predicate(host)` was truthy when that change occurred.
:meth:`.LoadBalancingPolicy.make_query_plan` and filters the results.

Note that this filtering may break desirable properties of the wrapped
policy in some cases. For instance, imagine if you configure this
policy to filter out ``host2``, and to wrap a round-robin policy that
rotates through three hosts in the order ``host1, host2, host3``,
``host2, host3, host1``, ``host3, host1, host2``, repeating. This
policy will yield ``host1, host3``, ``host3, host1``, ``host3, host1``,
disproportionately favoring ``host3``.
"""
child_qp = self._child_policy.make_query_plan(
working_keyspace=working_keyspace, query=query
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2 changes: 1 addition & 1 deletion docs/api/cassandra/policies.rst
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Expand Up @@ -26,7 +26,7 @@ Load Balancing

.. autoclass:: HostFilterPolicy

# we document these methods manually so we can specify a param to predicate
.. we document these methods manually so we can specify a param to predicate

.. automethod:: predicate(host)
.. automethod:: distance
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