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# Copyright 2014-2015 MongoDB, Inc.
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# Licensed under the Apache License, Version 2.0 (the "License"); you
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# may not use this file except in compliance with the License. You
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# may obtain a copy of the License at
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# http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied. See the License for the specific language governing
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# permissions and limitations under the License.
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"""Criteria to select some ServerDescriptions out of a list."""
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from pymongo.server_type import SERVER_TYPE
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def any_server_selector(server_descriptions):
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return server_descriptions
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def writable_server_selector(server_descriptions):
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return [s for s in server_descriptions if s.is_writable]
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def secondary_server_selector(server_descriptions):
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return [s for s in server_descriptions
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if s.server_type == SERVER_TYPE.RSSecondary]
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def arbiter_server_selector(server_descriptions):
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return [s for s in server_descriptions
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if s.server_type == SERVER_TYPE.RSArbiter]
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def writable_preferred_server_selector(server_descriptions):
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"""Like PrimaryPreferred but doesn't use tags or latency."""
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return writable_server_selector(server_descriptions) or server_descriptions
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def single_tag_set_server_selector(tag_set, server_descriptions):
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"""All servers matching one tag set.
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A tag set is a dict. A server matches if its tags are a superset:
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A server tagged {'a': '1', 'b': '2'} matches the tag set {'a': '1'}.
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The empty tag set {} matches any server.
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def tags_match(server_tags):
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for key, value in tag_set.items():
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if key not in server_tags or server_tags[key] != value:
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return [s for s in server_descriptions if tags_match(s.tags)]
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def tag_sets_server_selector(tag_sets, server_descriptions):
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"""All servers match a list of tag sets.
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tag_sets is a list of dicts. The empty tag set {} matches any server,
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and may be provided at the end of the list as a fallback. So
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[{'a': 'value'}, {}] expresses a preference for servers tagged
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{'a': 'value'}, but accepts any server if none matches the first
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for tag_set in tag_sets:
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selected = single_tag_set_server_selector(tag_set, server_descriptions)
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def apply_local_threshold(latency_ms, server_descriptions):
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"""All servers with round trip times within latency_ms of the fastest one.
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No ServerDescription's round_trip_time can be None.
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if not server_descriptions:
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# Avoid ValueError from min() with empty sequence.
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# round_trip_time is in seconds.
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if any(s for s in server_descriptions if s.round_trip_time is None):
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raise ValueError("Not all servers' round trip times are known")
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fastest = min(s.round_trip_time for s in server_descriptions)
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s for s in server_descriptions
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if (s.round_trip_time - fastest) < latency_ms / 1000.]
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def secondary_with_tags_server_selector(tag_sets, server_descriptions):
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"""All near-enough secondaries matching the tag sets."""
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return tag_sets_server_selector(
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tag_sets, secondary_server_selector(server_descriptions))
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def member_with_tags_server_selector(tag_sets, server_descriptions):
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"""All near-enough members matching the tag sets."""
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return tag_sets_server_selector(tag_sets, server_descriptions)
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pymongo/server_selectors.py
