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76d21d14a0
The function is used for two purposes: 1) for subscribers of streams to get a token they can use to get further updates with, and 2) for replication to track position of the writers of the stream. For streams with a single writer the two scenarios produce the same result, however the situation becomes complicated for streams with multiple writers. The current `MultiWriterIdGenerator` does not correctly handle the first case (which is not an issue as its only used for the `caches` stream which nothing subscribes to outside of replication).
44 lines
1.4 KiB
Python
44 lines
1.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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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 implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from synapse.storage.util.id_generators import _load_current_id
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class SlavedIdTracker(object):
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def __init__(self, db_conn, table, column, extra_tables=[], step=1):
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self.step = step
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self._current = _load_current_id(db_conn, table, column, step)
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for table, column in extra_tables:
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self.advance(_load_current_id(db_conn, table, column))
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def advance(self, new_id):
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self._current = (max if self.step > 0 else min)(self._current, new_id)
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def get_current_token(self):
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"""
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Returns:
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int
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"""
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return self._current
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def get_current_token_for_writer(self, instance_name: str) -> int:
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"""Returns the position of the given writer.
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For streams with single writers this is equivalent to
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`get_current_token`.
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"""
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return self.get_current_token()
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