678 lines
25 KiB
Python
678 lines
25 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2014-2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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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 typing import Dict, List, Optional, Set, Tuple, Union
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import attr
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.storage.database import DatabasePool, LoggingTransaction
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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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class IdGenerator:
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def __init__(self, db_conn, table, column):
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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):
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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(db_conn, table, column, step=1):
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"""
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Args:
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db_conn (object):
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table (str):
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column (str):
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step (int):
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Returns:
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int
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"""
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# debug logging for https://github.com/matrix-org/synapse/issues/7968
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logger.info("initialising stream generator for %s(%s)", table, column)
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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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(val,) = cur.fetchone()
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cur.close()
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current_id = int(val) if val else step
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return (max if step > 0 else min)(current_id, step)
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class StreamIdGenerator:
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"""Used to generate new stream ids when persisting events while keeping
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track of which transactions have been completed.
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This allows us to get the "current" stream id, i.e. the stream id such that
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all ids less than or equal to it have completed. This handles the fact that
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persistence of events can complete out of order.
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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__(self, db_conn, table, column, extra_tables=[], step=1):
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assert step != 0
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self._lock = threading.Lock()
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self._step = step
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self._current = _load_current_id(db_conn, table, column, step)
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for table, column in extra_tables:
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self._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() # type: OrderedDict[int, int]
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def get_next(self):
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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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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():
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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):
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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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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():
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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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"""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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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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"""Returns the position of the given writer.
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For streams with single writers this is equivalent to
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`get_current_token`.
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"""
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return self.get_current_token()
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class MultiWriterIdGenerator:
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"""An ID generator that tracks a stream that can have 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,
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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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):
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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 = {} # type: 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 = set() # type: Set[int]
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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() # type: Set[int]
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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 = [] # type: List[int]
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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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def _load_current_ids(
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self,
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db_conn,
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tables: List[Tuple[str, str, str]],
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):
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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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(stream_id,) = cur.fetchone()
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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 = []
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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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rows.extend(cur)
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# Sort so that we handle rows in order for each instance.
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rows.sort()
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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) -> int:
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return self._sequence_gen.get_next_id_txn(txn)
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def _load_next_mult_id_txn(self, txn, n: int) -> List[int]:
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return self._sequence_gen.get_next_mult_txn(txn, n)
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def get_next(self):
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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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return _MultiWriterCtxManager(self)
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def get_next_mult(self, n: int):
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"""
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Usage:
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async with stream_id_gen.get_next_mult(5) as stream_ids:
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# ... persist events ...
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"""
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return _MultiWriterCtxManager(self, n)
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def get_next_txn(self, txn: LoggingTransaction):
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"""
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Usage:
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stream_id = stream_id_gen.get_next(txn)
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# ... persist event ...
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"""
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next_id = self._load_next_id_txn(txn)
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with self._lock:
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self._unfinished_ids.add(next_id)
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txn.call_after(self._mark_id_as_finished, next_id)
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txn.call_on_exception(self._mark_id_as_finished, next_id)
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# Update the `stream_positions` table with newly updated stream
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# ID (unless self._writers is not set in which case we don't
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# bother, as nothing will read it).
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#
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# We only do this on the success path so that the persisted current
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# position points to a persisted row with the correct instance name.
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if self._writers:
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txn.call_after(
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run_as_background_process,
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"MultiWriterIdGenerator._update_table",
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self._db.runInteraction,
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"MultiWriterIdGenerator._update_table",
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self._update_stream_positions_table_txn,
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)
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return self._return_factor * next_id
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def _mark_id_as_finished(self, next_id: int):
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"""The ID has finished being processed so we should advance the
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current position if possible.
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"""
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with self._lock:
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self._unfinished_ids.discard(next_id)
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self._finished_ids.add(next_id)
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new_cur = None # type: Optional[int]
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if self._unfinished_ids:
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# If there are unfinished IDs then the new position will be the
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# largest finished ID less than the minimum unfinished ID.
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finished = set()
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min_unfinshed = min(self._unfinished_ids)
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for s in self._finished_ids:
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if s < min_unfinshed:
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if new_cur is None or new_cur < s:
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new_cur = s
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else:
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finished.add(s)
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# We clear these out since they're now all less than the new
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# position.
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self._finished_ids = finished
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else:
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# There are no unfinished IDs so the new position is simply the
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# largest finished one.
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new_cur = max(self._finished_ids)
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# We clear these out since they're now all less than the new
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# position.
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self._finished_ids.clear()
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if new_cur:
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curr = self._current_positions.get(self._instance_name, 0)
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self._current_positions[self._instance_name] = max(curr, new_cur)
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self._add_persisted_position(next_id)
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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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"""
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return self.get_persisted_upto_position()
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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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# If we don't have an entry for the given instance name, we assume it's a
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# new writer.
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#
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# For new writers we assume their initial position to be the current
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# persisted up to position. This stops Synapse from doing a full table
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# scan when a new writer announces itself over replication.
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with self._lock:
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return self._return_factor * self._current_positions.get(
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instance_name, self._persisted_upto_position
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)
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def get_positions(self) -> Dict[str, int]:
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"""Get a copy of the current positon map.
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Note that this won't necessarily include all configured writers if some
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writers haven't written anything yet.
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"""
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with self._lock:
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return {
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name: self._return_factor * i
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for name, i in self._current_positions.items()
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}
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def advance(self, instance_name: str, new_id: int):
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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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new_id *= self._return_factor
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with self._lock:
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self._current_positions[instance_name] = max(
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new_id, self._current_positions.get(instance_name, 0)
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)
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self._add_persisted_position(new_id)
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def get_persisted_upto_position(self) -> int:
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"""Get the max position where all previous positions have been
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persisted.
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|
|
|
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):
|
|
"""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:
|
|
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):
|
|
"""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(slots=True)
|
|
class _AsyncCtxManagerWrapper:
|
|
"""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 = attr.ib()
|
|
|
|
async def __aenter__(self):
|
|
return self.inner.__enter__()
|
|
|
|
async def __aexit__(self, exc_type, exc, tb):
|
|
return self.inner.__exit__(exc_type, exc, tb)
|
|
|
|
|
|
@attr.s(slots=True)
|
|
class _MultiWriterCtxManager:
|
|
"""Async context manager returned by MultiWriterIdGenerator"""
|
|
|
|
id_gen = attr.ib(type=MultiWriterIdGenerator)
|
|
multiple_ids = attr.ib(type=Optional[int], default=None)
|
|
stream_ids = attr.ib(type=List[int], 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,
|
|
)
|
|
|
|
with self.id_gen._lock:
|
|
self.id_gen._unfinished_ids.update(self.stream_ids)
|
|
|
|
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, exc, tb):
|
|
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
|