diff options
Diffstat (limited to 'synapse/storage/util')
| -rw-r--r-- | synapse/storage/util/id_generators.py | 116 |
1 files changed, 62 insertions, 54 deletions
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py index ac56bc9a05..4ff3013908 100644 --- a/synapse/storage/util/id_generators.py +++ b/synapse/storage/util/id_generators.py @@ -89,31 +89,77 @@ def _load_current_id( return (max if step > 0 else min)(current_id, step) -class AbstractStreamIdGenerator(metaclass=abc.ABCMeta): - @abc.abstractmethod - def get_next(self) -> AsyncContextManager[int]: - raise NotImplementedError() +class AbstractStreamIdTracker(metaclass=abc.ABCMeta): + """Tracks the "current" stream ID of a stream that may have multiple writers. + + Stream IDs are monotonically increasing or decreasing integers representing write + transactions. The "current" stream ID is the stream ID such that all transactions + with equal or smaller stream IDs have completed. Since transactions may complete out + of order, this is not the same as the stream ID of the last completed transaction. + + Completed transactions include both committed transactions and transactions that + have been rolled back. + """ @abc.abstractmethod - def get_next_mult(self, n: int) -> AsyncContextManager[Sequence[int]]: + def advance(self, instance_name: str, new_id: int) -> None: + """Advance the position of the named writer to the given ID, if greater + than existing entry. + """ raise NotImplementedError() @abc.abstractmethod def get_current_token(self) -> int: + """Returns the maximum stream id such that all stream ids less than or + equal to it have been successfully persisted. + + Returns: + The maximum stream id. + """ raise NotImplementedError() @abc.abstractmethod def get_current_token_for_writer(self, instance_name: str) -> int: + """Returns the position of the given writer. + + For streams with single writers this is equivalent to `get_current_token`. + """ + raise NotImplementedError() + + +class AbstractStreamIdGenerator(AbstractStreamIdTracker): + """Generates stream IDs for a stream that may have multiple writers. + + Each stream ID represents a write transaction, whose completion is tracked + so that the "current" stream ID of the stream can be determined. + + See `AbstractStreamIdTracker` for more details. + """ + + @abc.abstractmethod + def get_next(self) -> AsyncContextManager[int]: + """ + Usage: + async with stream_id_gen.get_next() as stream_id: + # ... persist event ... + """ + raise NotImplementedError() + + @abc.abstractmethod + def get_next_mult(self, n: int) -> AsyncContextManager[Sequence[int]]: + """ + Usage: + async with stream_id_gen.get_next(n) as stream_ids: + # ... persist events ... + """ raise NotImplementedError() class StreamIdGenerator(AbstractStreamIdGenerator): - """Used to generate new stream ids when persisting events while keeping - track of which transactions have been completed. + """Generates and tracks stream IDs for a stream with a single writer. - This allows us to get the "current" stream id, i.e. the stream id such that - all ids less than or equal to it have completed. This handles the fact that - persistence of events can complete out of order. + This class must only be used when the current Synapse process is the sole + writer for a stream. Args: db_conn(connection): A database connection to use to fetch the @@ -157,12 +203,12 @@ class StreamIdGenerator(AbstractStreamIdGenerator): # The key and values are the same, but we never look at the values. self._unfinished_ids: OrderedDict[int, int] = OrderedDict() + def advance(self, instance_name: str, new_id: int) -> None: + # `StreamIdGenerator` should only be used when there is a single writer, + # so replication should never happen. + raise Exception("Replication is not supported by StreamIdGenerator") + def get_next(self) -> AsyncContextManager[int]: - """ - Usage: - async with stream_id_gen.get_next() as stream_id: - # ... persist event ... - """ with self._lock: self._current += self._step next_id = self._current @@ -180,11 +226,6 @@ class StreamIdGenerator(AbstractStreamIdGenerator): return _AsyncCtxManagerWrapper(manager()) def get_next_mult(self, n: int) -> AsyncContextManager[Sequence[int]]: - """ - Usage: - async with stream_id_gen.get_next(n) as stream_ids: - # ... persist events ... - """ with self._lock: next_ids = range( self._current + self._step, @@ -208,12 +249,6 @@ class StreamIdGenerator(AbstractStreamIdGenerator): return _AsyncCtxManagerWrapper(manager()) def get_current_token(self) -> int: - """Returns the maximum stream id such that all stream ids less than or - equal to it have been successfully persisted. - - Returns: - The maximum stream id. - """ with self._lock: if self._unfinished_ids: return next(iter(self._unfinished_ids)) - self._step @@ -221,16 +256,11 @@ class StreamIdGenerator(AbstractStreamIdGenerator): return self._current def get_current_token_for_writer(self, instance_name: str) -> int: - """Returns the position of the given writer. - - For streams with single writers this is equivalent to - `get_current_token`. - """ return self.get_current_token() class MultiWriterIdGenerator(AbstractStreamIdGenerator): - """An ID generator that tracks a stream that can have multiple writers. + """Generates and tracks stream IDs for a stream with multiple writers. Uses a Postgres sequence to coordinate ID assignment, but positions of other writers will only get updated when `advance` is called (by replication). @@ -475,12 +505,6 @@ class MultiWriterIdGenerator(AbstractStreamIdGenerator): return stream_ids def get_next(self) -> AsyncContextManager[int]: - """ - Usage: - async with stream_id_gen.get_next() as stream_id: - # ... persist event ... - """ - # If we have a list of instances that are allowed to write to this # stream, make sure we're in it. if self._writers and self._instance_name not in self._writers: @@ -492,12 +516,6 @@ class MultiWriterIdGenerator(AbstractStreamIdGenerator): return cast(AsyncContextManager[int], _MultiWriterCtxManager(self)) def get_next_mult(self, n: int) -> AsyncContextManager[List[int]]: - """ - Usage: - async with stream_id_gen.get_next_mult(5) as stream_ids: - # ... persist events ... - """ - # If we have a list of instances that are allowed to write to this # stream, make sure we're in it. if self._writers and self._instance_name not in self._writers: @@ -597,15 +615,9 @@ class MultiWriterIdGenerator(AbstractStreamIdGenerator): self._add_persisted_position(next_id) def get_current_token(self) -> int: - """Returns the maximum stream id such that all stream ids less than or - equal to it have been successfully persisted. - """ - return self.get_persisted_upto_position() def get_current_token_for_writer(self, instance_name: str) -> int: - """Returns the position of the given writer.""" - # If we don't have an entry for the given instance name, we assume it's a # new writer. # @@ -631,10 +643,6 @@ class MultiWriterIdGenerator(AbstractStreamIdGenerator): } def advance(self, instance_name: str, new_id: int) -> None: - """Advance the position of the named writer to the given ID, if greater - than existing entry. - """ - new_id *= self._return_factor with self._lock: |