828 lines
31 KiB
Python
828 lines
31 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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) -> 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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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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# `StreamIdGenerator` should only be used when there is a single writer,
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# so replication should never happen.
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raise Exception("Replication is not supported by StreamIdGenerator")
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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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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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|
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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)
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self._max_seen_allocated_stream_id = max(
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self._max_seen_allocated_stream_id, self._unfinished_ids[-1]
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)
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finally:
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with self._lock:
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self._in_flight_fetches.remove(current_max)
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return stream_ids
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|
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def get_next(self) -> AsyncContextManager[int]:
|
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# If we have a list of instances that are allowed to write to this
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# 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
|