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![Nick Mills-Barrett](/assets/img/avatar_default.png)
This matches the multi instance writer ID generator class which can both handle advancing the current token over replication and by calling the database.
835 lines
32 KiB
Python
835 lines
32 KiB
Python
# Copyright 2014-2016 OpenMarket Ltd
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# Copyright 2021 The Matrix.org Foundation C.I.C.
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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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import abc
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import heapq
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import logging
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import threading
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from collections import OrderedDict
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from contextlib import contextmanager
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from types import TracebackType
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from typing import (
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AsyncContextManager,
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ContextManager,
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Dict,
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Generator,
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Generic,
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Iterable,
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List,
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Optional,
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Sequence,
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Set,
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Tuple,
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Type,
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TypeVar,
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Union,
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cast,
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)
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import attr
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from sortedcontainers import SortedList, SortedSet
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.storage.database import (
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DatabasePool,
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LoggingDatabaseConnection,
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LoggingTransaction,
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)
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from synapse.storage.types import Cursor
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from synapse.storage.util.sequence import PostgresSequenceGenerator
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logger = logging.getLogger(__name__)
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T = TypeVar("T")
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class IdGenerator:
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def __init__(
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self,
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db_conn: LoggingDatabaseConnection,
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table: str,
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column: str,
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):
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self._lock = threading.Lock()
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self._next_id = _load_current_id(db_conn, table, column)
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def get_next(self) -> int:
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with self._lock:
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self._next_id += 1
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return self._next_id
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def _load_current_id(
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db_conn: LoggingDatabaseConnection, table: str, column: str, step: int = 1
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) -> int:
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cur = db_conn.cursor(txn_name="_load_current_id")
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if step == 1:
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cur.execute("SELECT MAX(%s) FROM %s" % (column, table))
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else:
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cur.execute("SELECT MIN(%s) FROM %s" % (column, table))
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result = cur.fetchone()
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assert result is not None
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(val,) = result
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cur.close()
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current_id = int(val) if val else step
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res = (max if step > 0 else min)(current_id, step)
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logger.info("Initialising stream generator for %s(%s): %i", table, column, res)
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return res
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class AbstractStreamIdTracker(metaclass=abc.ABCMeta):
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"""Tracks the "current" stream ID of a stream that may have multiple writers.
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Stream IDs are monotonically increasing or decreasing integers representing write
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transactions. The "current" stream ID is the stream ID such that all transactions
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with equal or smaller stream IDs have completed. Since transactions may complete out
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of order, this is not the same as the stream ID of the last completed transaction.
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Completed transactions include both committed transactions and transactions that
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have been rolled back.
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"""
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@abc.abstractmethod
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def advance(self, instance_name: str, new_id: int) -> None:
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"""Advance the position of the named writer to the given ID, if greater
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than existing entry.
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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def get_current_token(self) -> int:
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"""Returns the maximum stream id such that all stream ids less than or
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equal to it have been successfully persisted.
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Returns:
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The maximum stream id.
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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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 `get_current_token`.
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"""
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raise NotImplementedError()
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class AbstractStreamIdGenerator(AbstractStreamIdTracker):
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"""Generates stream IDs for a stream that may have multiple writers.
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Each stream ID represents a write transaction, whose completion is tracked
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so that the "current" stream ID of the stream can be determined.
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See `AbstractStreamIdTracker` for more details.
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"""
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@abc.abstractmethod
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def get_next(self) -> AsyncContextManager[int]:
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"""
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Usage:
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async with stream_id_gen.get_next() as stream_id:
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# ... persist event ...
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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def get_next_mult(self, n: int) -> AsyncContextManager[Sequence[int]]:
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"""
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Usage:
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async with stream_id_gen.get_next(n) as stream_ids:
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# ... persist events ...
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"""
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raise NotImplementedError()
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class StreamIdGenerator(AbstractStreamIdGenerator):
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"""Generates and tracks stream IDs for a stream with a single writer.
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This class must only be used when the current Synapse process is the sole
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writer for a stream.
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Args:
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db_conn(connection): A database connection to use to fetch the
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initial value of the generator from.
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table(str): A database table to read the initial value of the id
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generator from.
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column(str): The column of the database table to read the initial
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value from the id generator from.
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extra_tables(list): List of pairs of database tables and columns to
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use to source the initial value of the generator from. The value
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with the largest magnitude is used.
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step(int): which direction the stream ids grow in. +1 to grow
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upwards, -1 to grow downwards.
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Usage:
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async with stream_id_gen.get_next() as stream_id:
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# ... persist event ...
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"""
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def __init__(
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self,
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db_conn: LoggingDatabaseConnection,
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table: str,
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column: str,
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extra_tables: Iterable[Tuple[str, str]] = (),
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step: int = 1,
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is_writer: bool = True,
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) -> None:
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assert step != 0
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self._lock = threading.Lock()
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self._step: int = step
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self._current: int = _load_current_id(db_conn, table, column, step)
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self._is_writer = is_writer
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for table, column in extra_tables:
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self._current = (max if step > 0 else min)(
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self._current, _load_current_id(db_conn, table, column, step)
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)
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# We use this as an ordered set, as we want to efficiently append items,
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# remove items and get the first item. Since we insert IDs in order, the
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# insertion ordering will ensure its in the correct ordering.
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#
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# The key and values are the same, but we never look at the values.
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self._unfinished_ids: OrderedDict[int, int] = OrderedDict()
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def advance(self, instance_name: str, new_id: int) -> None:
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# Advance should never be called on a writer instance, only over replication
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if self._is_writer:
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raise Exception("Replication is not supported by writer StreamIdGenerator")
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self._current = (max if self._step > 0 else min)(self._current, new_id)
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def get_next(self) -> AsyncContextManager[int]:
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with self._lock:
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self._current += self._step
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next_id = self._current
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self._unfinished_ids[next_id] = next_id
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@contextmanager
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def manager() -> Generator[int, None, None]:
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try:
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yield next_id
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finally:
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with self._lock:
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self._unfinished_ids.pop(next_id)
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return _AsyncCtxManagerWrapper(manager())
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def get_next_mult(self, n: int) -> AsyncContextManager[Sequence[int]]:
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with self._lock:
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next_ids = range(
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self._current + self._step,
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self._current + self._step * (n + 1),
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self._step,
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)
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self._current += n * self._step
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for next_id in next_ids:
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self._unfinished_ids[next_id] = next_id
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@contextmanager
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def manager() -> Generator[Sequence[int], None, None]:
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try:
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yield next_ids
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finally:
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with self._lock:
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for next_id in next_ids:
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self._unfinished_ids.pop(next_id)
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return _AsyncCtxManagerWrapper(manager())
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def get_current_token(self) -> int:
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if self._is_writer:
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return self._current
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with self._lock:
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if self._unfinished_ids:
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return next(iter(self._unfinished_ids)) - self._step
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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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return self.get_current_token()
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class MultiWriterIdGenerator(AbstractStreamIdGenerator):
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"""Generates and tracks stream IDs for a stream with multiple writers.
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Uses a Postgres sequence to coordinate ID assignment, but positions of other
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writers will only get updated when `advance` is called (by replication).
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Note: Only works with Postgres.
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Args:
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db_conn
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db
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stream_name: A name for the stream, for use in the `stream_positions`
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table. (Does not need to be the same as the replication stream name)
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instance_name: The name of this instance.
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tables: List of tables associated with the stream. Tuple of table
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name, column name that stores the writer's instance name, and
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column name that stores the stream ID.
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sequence_name: The name of the postgres sequence used to generate new
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IDs.
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writers: A list of known writers to use to populate current positions
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on startup. Can be empty if nothing uses `get_current_token` or
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`get_positions` (e.g. caches stream).
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positive: Whether the IDs are positive (true) or negative (false).
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When using negative IDs we go backwards from -1 to -2, -3, etc.
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"""
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def __init__(
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self,
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db_conn: LoggingDatabaseConnection,
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db: DatabasePool,
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stream_name: str,
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instance_name: str,
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tables: List[Tuple[str, str, str]],
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sequence_name: str,
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writers: List[str],
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positive: bool = True,
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) -> None:
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self._db = db
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self._stream_name = stream_name
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self._instance_name = instance_name
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self._positive = positive
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self._writers = writers
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self._return_factor = 1 if positive else -1
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# We lock as some functions may be called from DB threads.
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self._lock = threading.Lock()
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# Note: If we are a negative stream then we still store all the IDs as
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# positive to make life easier for us, and simply negate the IDs when we
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# return them.
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self._current_positions: Dict[str, int] = {}
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# Set of local IDs that we're still processing. The current position
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# should be less than the minimum of this set (if not empty).
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self._unfinished_ids: SortedSet[int] = SortedSet()
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# We also need to track when we've requested some new stream IDs but
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# they haven't yet been added to the `_unfinished_ids` set. Every time
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# we request a new stream ID we add the current max stream ID to the
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# list, and remove it once we've added the newly allocated IDs to the
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# `_unfinished_ids` set. This means that we *may* be allocated stream
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# IDs above those in the list, and so we can't advance the local current
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# position beyond the minimum stream ID in this list.
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self._in_flight_fetches: SortedList[int] = SortedList()
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# Set of local IDs that we've processed that are larger than the current
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# position, due to there being smaller unpersisted IDs.
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self._finished_ids: Set[int] = set()
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# We track the max position where we know everything before has been
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# persisted. This is done by a) looking at the min across all instances
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# and b) noting that if we have seen a run of persisted positions
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# without gaps (e.g. 5, 6, 7) then we can skip forward (e.g. to 7).
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#
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# Note: There is no guarantee that the IDs generated by the sequence
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# will be gapless; gaps can form when e.g. a transaction was rolled
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# back. This means that sometimes we won't be able to skip forward the
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# position even though everything has been persisted. However, since
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# gaps should be relatively rare it's still worth doing the book keeping
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# that allows us to skip forwards when there are gapless runs of
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# positions.
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#
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# We start at 1 here as a) the first generated stream ID will be 2, and
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# b) other parts of the code assume that stream IDs are strictly greater
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# than 0.
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self._persisted_upto_position = (
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min(self._current_positions.values()) if self._current_positions else 1
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)
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self._known_persisted_positions: List[int] = []
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# The maximum stream ID that we have seen been allocated across any writer.
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self._max_seen_allocated_stream_id = 1
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self._sequence_gen = PostgresSequenceGenerator(sequence_name)
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# We check that the table and sequence haven't diverged.
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for table, _, id_column in tables:
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self._sequence_gen.check_consistency(
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db_conn,
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table=table,
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id_column=id_column,
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stream_name=stream_name,
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positive=positive,
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)
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# This goes and fills out the above state from the database.
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self._load_current_ids(db_conn, tables)
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self._max_seen_allocated_stream_id = max(
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self._current_positions.values(), default=1
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)
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def _load_current_ids(
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self,
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db_conn: LoggingDatabaseConnection,
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tables: List[Tuple[str, str, str]],
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) -> None:
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cur = db_conn.cursor(txn_name="_load_current_ids")
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# Load the current positions of all writers for the stream.
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if self._writers:
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# We delete any stale entries in the positions table. This is
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# important if we add back a writer after a long time; we want to
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# consider that a "new" writer, rather than using the old stale
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# entry here.
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sql = """
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DELETE FROM stream_positions
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WHERE
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stream_name = ?
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AND instance_name != ALL(?)
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"""
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cur.execute(sql, (self._stream_name, self._writers))
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sql = """
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SELECT instance_name, stream_id FROM stream_positions
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WHERE stream_name = ?
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"""
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cur.execute(sql, (self._stream_name,))
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self._current_positions = {
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instance: stream_id * self._return_factor
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for instance, stream_id in cur
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if instance in self._writers
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}
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# We set the `_persisted_upto_position` to be the minimum of all current
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# positions. If empty we use the max stream ID from the DB table.
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min_stream_id = min(self._current_positions.values(), default=None)
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if min_stream_id is None:
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# We add a GREATEST here to ensure that the result is always
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# positive. (This can be a problem for e.g. backfill streams where
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# the server has never backfilled).
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max_stream_id = 1
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for table, _, id_column in tables:
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sql = """
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SELECT GREATEST(COALESCE(%(agg)s(%(id)s), 1), 1)
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FROM %(table)s
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""" % {
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"id": id_column,
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"table": table,
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"agg": "MAX" if self._positive else "-MIN",
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}
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cur.execute(sql)
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result = cur.fetchone()
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assert result is not None
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(stream_id,) = result
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max_stream_id = max(max_stream_id, stream_id)
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self._persisted_upto_position = max_stream_id
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else:
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# If we have a min_stream_id then we pull out everything greater
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# than it from the DB so that we can prefill
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# `_known_persisted_positions` and get a more accurate
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# `_persisted_upto_position`.
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#
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# We also check if any of the later rows are from this instance, in
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# which case we use that for this instance's current position. This
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# is to handle the case where we didn't finish persisting to the
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# stream positions table before restart (or the stream position
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# table otherwise got out of date).
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self._persisted_upto_position = min_stream_id
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rows: List[Tuple[str, int]] = []
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for table, instance_column, id_column in tables:
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sql = """
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SELECT %(instance)s, %(id)s FROM %(table)s
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WHERE ? %(cmp)s %(id)s
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""" % {
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"id": id_column,
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"table": table,
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"instance": instance_column,
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"cmp": "<=" if self._positive else ">=",
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}
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cur.execute(sql, (min_stream_id * self._return_factor,))
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# Cast safety: this corresponds to the types returned by the query above.
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rows.extend(cast(Iterable[Tuple[str, int]], cur))
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# Sort by stream_id (ascending, lowest -> highest) so that we handle
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# rows in order for each instance because we don't want to overwrite
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# the current_position of an instance to a lower stream ID than
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# we're actually at.
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def sort_by_stream_id_key_func(row: Tuple[str, int]) -> int:
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(instance, stream_id) = row
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# If `stream_id` is ever `None`, we will see a `TypeError: '<'
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# not supported between instances of 'NoneType' and 'X'` error.
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return stream_id
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rows.sort(key=sort_by_stream_id_key_func)
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with self._lock:
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for (
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instance,
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stream_id,
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) in rows:
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stream_id = self._return_factor * stream_id
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self._add_persisted_position(stream_id)
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if instance == self._instance_name:
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self._current_positions[instance] = stream_id
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cur.close()
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def _load_next_id_txn(self, txn: Cursor) -> int:
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stream_ids = self._load_next_mult_id_txn(txn, 1)
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return stream_ids[0]
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def _load_next_mult_id_txn(self, txn: Cursor, n: int) -> List[int]:
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# We need to track that we've requested some more stream IDs, and what
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# the current max allocated stream ID is. This is to prevent a race
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# where we've been allocated stream IDs but they have not yet been added
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# to the `_unfinished_ids` set, allowing the current position to advance
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# past them.
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with self._lock:
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current_max = self._max_seen_allocated_stream_id
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self._in_flight_fetches.add(current_max)
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try:
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stream_ids = self._sequence_gen.get_next_mult_txn(txn, n)
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with self._lock:
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self._unfinished_ids.update(stream_ids)
|
|
self._max_seen_allocated_stream_id = max(
|
|
self._max_seen_allocated_stream_id, self._unfinished_ids[-1]
|
|
)
|
|
finally:
|
|
with self._lock:
|
|
self._in_flight_fetches.remove(current_max)
|
|
|
|
return stream_ids
|
|
|
|
def get_next(self) -> AsyncContextManager[int]:
|
|
# 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:
|
|
raise Exception("Tried to allocate stream ID on non-writer")
|
|
|
|
# Cast safety: the second argument to _MultiWriterCtxManager, multiple_ids,
|
|
# controls the return type. If `None` or omitted, the context manager yields
|
|
# a single integer stream_id; otherwise it yields a list of stream_ids.
|
|
return cast(AsyncContextManager[int], _MultiWriterCtxManager(self))
|
|
|
|
def get_next_mult(self, n: int) -> AsyncContextManager[List[int]]:
|
|
# 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:
|
|
raise Exception("Tried to allocate stream ID on non-writer")
|
|
|
|
# Cast safety: see get_next.
|
|
return cast(AsyncContextManager[List[int]], _MultiWriterCtxManager(self, n))
|
|
|
|
def get_next_txn(self, txn: LoggingTransaction) -> int:
|
|
"""
|
|
Usage:
|
|
|
|
stream_id = stream_id_gen.get_next(txn)
|
|
# ... 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:
|
|
raise Exception("Tried to allocate stream ID on non-writer")
|
|
|
|
next_id = self._load_next_id_txn(txn)
|
|
|
|
txn.call_after(self._mark_id_as_finished, next_id)
|
|
txn.call_on_exception(self._mark_id_as_finished, next_id)
|
|
|
|
# Update the `stream_positions` table with newly updated stream
|
|
# ID (unless self._writers is not set in which case we don't
|
|
# bother, as nothing will read it).
|
|
#
|
|
# We only do this on the success path so that the persisted current
|
|
# position points to a persisted row with the correct instance name.
|
|
if self._writers:
|
|
txn.call_after(
|
|
run_as_background_process,
|
|
"MultiWriterIdGenerator._update_table",
|
|
self._db.runInteraction,
|
|
"MultiWriterIdGenerator._update_table",
|
|
self._update_stream_positions_table_txn,
|
|
)
|
|
|
|
return self._return_factor * next_id
|
|
|
|
def _mark_id_as_finished(self, next_id: int) -> None:
|
|
"""The ID has finished being processed so we should advance the
|
|
current position if possible.
|
|
"""
|
|
|
|
with self._lock:
|
|
self._unfinished_ids.discard(next_id)
|
|
self._finished_ids.add(next_id)
|
|
|
|
new_cur: Optional[int] = None
|
|
|
|
if self._unfinished_ids or self._in_flight_fetches:
|
|
# If there are unfinished IDs then the new position will be the
|
|
# largest finished ID strictly less than the minimum unfinished
|
|
# ID.
|
|
|
|
# The minimum unfinished ID needs to take account of both
|
|
# `_unfinished_ids` and `_in_flight_fetches`.
|
|
if self._unfinished_ids and self._in_flight_fetches:
|
|
# `_in_flight_fetches` stores the maximum safe stream ID, so
|
|
# we add one to make it equivalent to the minimum unsafe ID.
|
|
min_unfinished = min(
|
|
self._unfinished_ids[0], self._in_flight_fetches[0] + 1
|
|
)
|
|
elif self._in_flight_fetches:
|
|
min_unfinished = self._in_flight_fetches[0] + 1
|
|
else:
|
|
min_unfinished = self._unfinished_ids[0]
|
|
|
|
finished = set()
|
|
for s in self._finished_ids:
|
|
if s < min_unfinished:
|
|
if new_cur is None or new_cur < s:
|
|
new_cur = s
|
|
else:
|
|
finished.add(s)
|
|
|
|
# We clear these out since they're now all less than the new
|
|
# position.
|
|
self._finished_ids = finished
|
|
else:
|
|
# There are no unfinished IDs so the new position is simply the
|
|
# largest finished one.
|
|
new_cur = max(self._finished_ids)
|
|
|
|
# We clear these out since they're now all less than the new
|
|
# position.
|
|
self._finished_ids.clear()
|
|
|
|
if new_cur:
|
|
curr = self._current_positions.get(self._instance_name, 0)
|
|
self._current_positions[self._instance_name] = max(curr, new_cur)
|
|
|
|
self._add_persisted_position(next_id)
|
|
|
|
def get_current_token(self) -> int:
|
|
return self.get_persisted_upto_position()
|
|
|
|
def get_current_token_for_writer(self, instance_name: str) -> int:
|
|
# If we don't have an entry for the given instance name, we assume it's a
|
|
# new writer.
|
|
#
|
|
# For new writers we assume their initial position to be the current
|
|
# persisted up to position. This stops Synapse from doing a full table
|
|
# scan when a new writer announces itself over replication.
|
|
with self._lock:
|
|
return self._return_factor * self._current_positions.get(
|
|
instance_name, self._persisted_upto_position
|
|
)
|
|
|
|
def get_positions(self) -> Dict[str, int]:
|
|
"""Get a copy of the current positon map.
|
|
|
|
Note that this won't necessarily include all configured writers if some
|
|
writers haven't written anything yet.
|
|
"""
|
|
|
|
with self._lock:
|
|
return {
|
|
name: self._return_factor * i
|
|
for name, i in self._current_positions.items()
|
|
}
|
|
|
|
def advance(self, instance_name: str, new_id: int) -> None:
|
|
new_id *= self._return_factor
|
|
|
|
with self._lock:
|
|
self._current_positions[instance_name] = max(
|
|
new_id, self._current_positions.get(instance_name, 0)
|
|
)
|
|
|
|
self._max_seen_allocated_stream_id = max(
|
|
self._max_seen_allocated_stream_id, new_id
|
|
)
|
|
|
|
self._add_persisted_position(new_id)
|
|
|
|
def get_persisted_upto_position(self) -> int:
|
|
"""Get the max position where all previous positions have been
|
|
persisted.
|
|
|
|
Note: In the worst case scenario this will be equal to the minimum
|
|
position across writers. This means that the returned position here can
|
|
lag if one writer doesn't write very often.
|
|
"""
|
|
|
|
with self._lock:
|
|
return self._return_factor * self._persisted_upto_position
|
|
|
|
def _add_persisted_position(self, new_id: int) -> None:
|
|
"""Record that we have persisted a position.
|
|
|
|
This is used to keep the `_current_positions` up to date.
|
|
"""
|
|
|
|
# We require that the lock is locked by caller
|
|
assert self._lock.locked()
|
|
|
|
heapq.heappush(self._known_persisted_positions, new_id)
|
|
|
|
# If we're a writer and we don't have any active writes we update our
|
|
# current position to the latest position seen. This allows the instance
|
|
# to report a recent position when asked, rather than a potentially old
|
|
# one (if this instance hasn't written anything for a while).
|
|
our_current_position = self._current_positions.get(self._instance_name)
|
|
if (
|
|
our_current_position
|
|
and not self._unfinished_ids
|
|
and not self._in_flight_fetches
|
|
):
|
|
self._current_positions[self._instance_name] = max(
|
|
our_current_position, new_id
|
|
)
|
|
|
|
# We move the current min position up if the minimum current positions
|
|
# of all instances is higher (since by definition all positions less
|
|
# that that have been persisted).
|
|
min_curr = min(self._current_positions.values(), default=0)
|
|
self._persisted_upto_position = max(min_curr, self._persisted_upto_position)
|
|
|
|
# We now iterate through the seen positions, discarding those that are
|
|
# less than the current min positions, and incrementing the min position
|
|
# if its exactly one greater.
|
|
#
|
|
# This is also where we discard items from `_known_persisted_positions`
|
|
# (to ensure the list doesn't infinitely grow).
|
|
while self._known_persisted_positions:
|
|
if self._known_persisted_positions[0] <= self._persisted_upto_position:
|
|
heapq.heappop(self._known_persisted_positions)
|
|
elif (
|
|
self._known_persisted_positions[0] == self._persisted_upto_position + 1
|
|
):
|
|
heapq.heappop(self._known_persisted_positions)
|
|
self._persisted_upto_position += 1
|
|
else:
|
|
# There was a gap in seen positions, so there is nothing more to
|
|
# do.
|
|
break
|
|
|
|
def _update_stream_positions_table_txn(self, txn: Cursor) -> None:
|
|
"""Update the `stream_positions` table with newly persisted position."""
|
|
|
|
if not self._writers:
|
|
return
|
|
|
|
# We upsert the value, ensuring on conflict that we always increase the
|
|
# value (or decrease if stream goes backwards).
|
|
sql = """
|
|
INSERT INTO stream_positions (stream_name, instance_name, stream_id)
|
|
VALUES (?, ?, ?)
|
|
ON CONFLICT (stream_name, instance_name)
|
|
DO UPDATE SET
|
|
stream_id = %(agg)s(stream_positions.stream_id, EXCLUDED.stream_id)
|
|
""" % {
|
|
"agg": "GREATEST" if self._positive else "LEAST",
|
|
}
|
|
|
|
pos = (self.get_current_token_for_writer(self._instance_name),)
|
|
txn.execute(sql, (self._stream_name, self._instance_name, pos))
|
|
|
|
|
|
@attr.s(frozen=True, auto_attribs=True)
|
|
class _AsyncCtxManagerWrapper(Generic[T]):
|
|
"""Helper class to convert a plain context manager to an async one.
|
|
|
|
This is mainly useful if you have a plain context manager but the interface
|
|
requires an async one.
|
|
"""
|
|
|
|
inner: ContextManager[T]
|
|
|
|
async def __aenter__(self) -> T:
|
|
return self.inner.__enter__()
|
|
|
|
async def __aexit__(
|
|
self,
|
|
exc_type: Optional[Type[BaseException]],
|
|
exc: Optional[BaseException],
|
|
tb: Optional[TracebackType],
|
|
) -> Optional[bool]:
|
|
return self.inner.__exit__(exc_type, exc, tb)
|
|
|
|
|
|
@attr.s(slots=True, auto_attribs=True)
|
|
class _MultiWriterCtxManager:
|
|
"""Async context manager returned by MultiWriterIdGenerator"""
|
|
|
|
id_gen: MultiWriterIdGenerator
|
|
multiple_ids: Optional[int] = None
|
|
stream_ids: List[int] = attr.Factory(list)
|
|
|
|
async def __aenter__(self) -> Union[int, List[int]]:
|
|
# It's safe to run this in autocommit mode as fetching values from a
|
|
# sequence ignores transaction semantics anyway.
|
|
self.stream_ids = await self.id_gen._db.runInteraction(
|
|
"_load_next_mult_id",
|
|
self.id_gen._load_next_mult_id_txn,
|
|
self.multiple_ids or 1,
|
|
db_autocommit=True,
|
|
)
|
|
|
|
if self.multiple_ids is None:
|
|
return self.stream_ids[0] * self.id_gen._return_factor
|
|
else:
|
|
return [i * self.id_gen._return_factor for i in self.stream_ids]
|
|
|
|
async def __aexit__(
|
|
self,
|
|
exc_type: Optional[Type[BaseException]],
|
|
exc: Optional[BaseException],
|
|
tb: Optional[TracebackType],
|
|
) -> bool:
|
|
for i in self.stream_ids:
|
|
self.id_gen._mark_id_as_finished(i)
|
|
|
|
if exc_type is not None:
|
|
return False
|
|
|
|
# Update the `stream_positions` table with newly updated stream
|
|
# ID (unless self._writers is not set in which case we don't
|
|
# bother, as nothing will read it).
|
|
#
|
|
# We only do this on the success path so that the persisted current
|
|
# position points to a persisted row with the correct instance name.
|
|
#
|
|
# We do this in autocommit mode as a) the upsert works correctly outside
|
|
# transactions and b) reduces the amount of time the rows are locked
|
|
# for. If we don't do this then we'll often hit serialization errors due
|
|
# to the fact we default to REPEATABLE READ isolation levels.
|
|
if self.id_gen._writers:
|
|
await self.id_gen._db.runInteraction(
|
|
"MultiWriterIdGenerator._update_table",
|
|
self.id_gen._update_stream_positions_table_txn,
|
|
db_autocommit=True,
|
|
)
|
|
|
|
return False
|