329 lines
10 KiB
Python
329 lines
10 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 contextlib
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import threading
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from collections import deque
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from typing import Dict, Set
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from typing_extensions import Deque
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from synapse.storage.database import DatabasePool, LoggingTransaction
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from synapse.storage.util.sequence import PostgresSequenceGenerator
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class IdGenerator(object):
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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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cur = db_conn.cursor()
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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(object):
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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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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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self._unfinished_ids = deque() # type: Deque[int]
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def get_next(self):
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"""
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Usage:
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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.append(next_id)
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@contextlib.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.remove(next_id)
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return manager()
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def get_next_mult(self, n):
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"""
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Usage:
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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.append(next_id)
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@contextlib.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.remove(next_id)
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return manager()
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def get_current_token(self):
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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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int
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"""
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with self._lock:
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if self._unfinished_ids:
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return self._unfinished_ids[0] - 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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instance_name: The name of this instance.
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table: Database table associated with stream.
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instance_column: Column that stores the row's writer's instance name
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id_column: Column 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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"""
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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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instance_name: str,
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table: str,
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instance_column: str,
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id_column: str,
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sequence_name: str,
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):
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self._db = db
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self._instance_name = instance_name
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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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self._current_positions = self._load_current_ids(
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db_conn, table, instance_column, id_column
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)
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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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self._sequence_gen = PostgresSequenceGenerator(sequence_name)
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def _load_current_ids(
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self, db_conn, table: str, instance_column: str, id_column: str
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) -> Dict[str, int]:
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sql = """
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SELECT %(instance)s, MAX(%(id)s) FROM %(table)s
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GROUP BY %(instance)s
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""" % {
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"instance": instance_column,
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"id": id_column,
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"table": table,
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}
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cur = db_conn.cursor()
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cur.execute(sql)
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# `cur` is an iterable over returned rows, which are 2-tuples.
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current_positions = dict(cur)
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cur.close()
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return current_positions
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def _load_next_id_txn(self, txn):
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return self._sequence_gen.get_next_id_txn(txn)
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async def get_next(self):
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"""
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Usage:
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with await stream_id_gen.get_next() as stream_id:
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# ... persist event ...
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"""
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next_id = await self._db.runInteraction("_load_next_id", self._load_next_id_txn)
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# Assert the fetched ID is actually greater than what we currently
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# believe the ID to be. If not, then the sequence and table have got
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# out of sync somehow.
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assert self.get_current_token_for_writer(self._instance_name) < next_id
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with self._lock:
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self._unfinished_ids.add(next_id)
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@contextlib.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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self._mark_id_as_finished(next_id)
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return manager()
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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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return 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 poistion 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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# Figure out if its safe to advance the position by checking there
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# aren't any lower allocated IDs that are yet to finish.
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if all(c > next_id for c in self._unfinished_ids):
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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, 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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# Currently we don't support this operation, as it's not obvious how to
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# condense the stream positions of multiple writers into a single int.
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raise NotImplementedError()
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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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"""
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with self._lock:
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return self._current_positions.get(instance_name, 0)
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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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"""
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with self._lock:
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return dict(self._current_positions)
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def advance(self, instance_name: str, new_id: int):
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"""Advance the postion 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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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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