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Add MultiWriterIdGenerator. (#7281)

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This will be used to coordinate stream IDs across multiple writers.

Functions as the equivalent of both `StreamIdGenerator` and
`SlavedIdTracker`.
This commit is contained in:
Erik Johnston 2020-05-04 17:17:45 +01:00 committed by GitHub
parent 15aa09bbe6
commit 8123b2f909
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4 changed files with 353 additions and 2 deletions
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1
changelog.d/7281.misc Normal file
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@ -0,0 +1 @@
Add MultiWriterIdGenerator to support multiple concurrent writers of streams.

169
synapse/storage/util/id_generators.py
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@ -16,6 +16,11 @@
import contextlib
import threading
from collections import deque
from typing import Dict, Set, Tuple
from typing_extensions import Deque
from synapse.storage.database import Database, LoggingTransaction
class IdGenerator(object):
@ -87,7 +92,7 @@ class StreamIdGenerator(object):
self._current = (max if step > 0 else min)(
self._current, _load_current_id(db_conn, table, column, step)
)
self._unfinished_ids = deque()
self._unfinished_ids = deque() # type: Deque[int]
def get_next(self):
"""
@ -163,7 +168,7 @@ class ChainedIdGenerator(object):
self.chained_generator = chained_generator
self._lock = threading.Lock()
self._current_max = _load_current_id(db_conn, table, column)
self._unfinished_ids = deque()
self._unfinished_ids = deque() # type: Deque[Tuple[int, int]]
def get_next(self):
"""
@ -198,3 +203,163 @@ class ChainedIdGenerator(object):
return stream_id - 1, chained_id
return self._current_max, self.chained_generator.get_current_token()
class MultiWriterIdGenerator:
"""An ID generator that tracks a stream that can have multiple writers.
Uses a Postgres sequence to coordinate ID assignment, but positions of other
writers will only get updated when `advance` is called (by replication).
Note: Only works with Postgres.
Args:
db_conn
db
instance_name: The name of this instance.
table: Database table associated with stream.
instance_column: Column that stores the row's writer's instance name
id_column: Column that stores the stream ID.
sequence_name: The name of the postgres sequence used to generate new
IDs.
"""
def __init__(
self,
db_conn,
db: Database,
instance_name: str,
table: str,
instance_column: str,
id_column: str,
sequence_name: str,
):
self._db = db
self._instance_name = instance_name
self._sequence_name = sequence_name
# We lock as some functions may be called from DB threads.
self._lock = threading.Lock()
self._current_positions = self._load_current_ids(
db_conn, table, instance_column, id_column
)
# Set of local IDs that we're still processing. The current position
# should be less than the minimum of this set (if not empty).
self._unfinished_ids = set() # type: Set[int]
def _load_current_ids(
self, db_conn, table: str, instance_column: str, id_column: str
) -> Dict[str, int]:
sql = """
SELECT %(instance)s, MAX(%(id)s) FROM %(table)s
GROUP BY %(instance)s
""" % {
"instance": instance_column,
"id": id_column,
"table": table,
}
cur = db_conn.cursor()
cur.execute(sql)
# `cur` is an iterable over returned rows, which are 2-tuples.
current_positions = dict(cur)
cur.close()
return current_positions
def _load_next_id_txn(self, txn):
txn.execute("SELECT nextval(?)", (self._sequence_name,))
(next_id,) = txn.fetchone()
return next_id
async def get_next(self):
"""
Usage:
with await stream_id_gen.get_next() as stream_id:
# ... persist event ...
"""
next_id = await self._db.runInteraction("_load_next_id", self._load_next_id_txn)
# Assert the fetched ID is actually greater than what we currently
# believe the ID to be. If not, then the sequence and table have got
# out of sync somehow.
assert self.get_current_token() < next_id
with self._lock:
self._unfinished_ids.add(next_id)
@contextlib.contextmanager
def manager():
try:
yield next_id
finally:
self._mark_id_as_finished(next_id)
return manager()
def get_next_txn(self, txn: LoggingTransaction):
"""
Usage:
stream_id = stream_id_gen.get_next(txn)
# ... persist event ...
"""
next_id = self._load_next_id_txn(txn)
with self._lock:
self._unfinished_ids.add(next_id)
txn.call_after(self._mark_id_as_finished, next_id)
txn.call_on_exception(self._mark_id_as_finished, next_id)
return next_id
def _mark_id_as_finished(self, next_id: int):
"""The ID has finished being processed so we should advance the
current poistion if possible.
"""
with self._lock:
self._unfinished_ids.discard(next_id)
# Figure out if its safe to advance the position by checking there
# aren't any lower allocated IDs that are yet to finish.
if all(c > next_id for c in self._unfinished_ids):
curr = self._current_positions.get(self._instance_name, 0)
self._current_positions[self._instance_name] = max(curr, next_id)
def get_current_token(self, instance_name: str = None) -> int:
"""Gets the current position of a named writer (defaults to current
instance).
Returns 0 if we don't have a position for the named writer (likely due
to it being a new writer).
"""
if instance_name is None:
instance_name = self._instance_name
with self._lock:
return self._current_positions.get(instance_name, 0)
def get_positions(self) -> Dict[str, int]:
"""Get a copy of the current positon map.
"""
with self._lock:
return dict(self._current_positions)
def advance(self, instance_name: str, new_id: int):
"""Advance the postion of the named writer to the given ID, if greater
than existing entry.
"""
with self._lock:
self._current_positions[instance_name] = max(
new_id, self._current_positions.get(instance_name, 0)
)

184
tests/storage/test_id_generators.py Normal file
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@ -0,0 +1,184 @@
# -*- coding: utf-8 -*-
# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from synapse.storage.database import Database
from synapse.storage.util.id_generators import MultiWriterIdGenerator
from tests.unittest import HomeserverTestCase
from tests.utils import USE_POSTGRES_FOR_TESTS
class MultiWriterIdGeneratorTestCase(HomeserverTestCase):
if not USE_POSTGRES_FOR_TESTS:
skip = "Requires Postgres"
def prepare(self, reactor, clock, hs):
self.store = hs.get_datastore()
self.db = self.store.db # type: Database
self.get_success(self.db.runInteraction("_setup_db", self._setup_db))
def _setup_db(self, txn):
txn.execute("CREATE SEQUENCE foobar_seq")
txn.execute(
"""
CREATE TABLE foobar (
stream_id BIGINT NOT NULL,
instance_name TEXT NOT NULL,
data TEXT
);
"""
)
def _create_id_generator(self, instance_name="master") -> MultiWriterIdGenerator:
def _create(conn):
return MultiWriterIdGenerator(
conn,
self.db,
instance_name=instance_name,
table="foobar",
instance_column="instance_name",
id_column="stream_id",
sequence_name="foobar_seq",
)
return self.get_success(self.db.runWithConnection(_create))
def _insert_rows(self, instance_name: str, number: int):
def _insert(txn):
for _ in range(number):
txn.execute(
"INSERT INTO foobar VALUES (nextval('foobar_seq'), ?)",
(instance_name,),
)
self.get_success(self.db.runInteraction("test_single_instance", _insert))
def test_empty(self):
"""Test an ID generator against an empty database gives sensible
current positions.
"""
id_gen = self._create_id_generator()
# The table is empty so we expect an empty map for positions
self.assertEqual(id_gen.get_positions(), {})
def test_single_instance(self):
"""Test that reads and writes from a single process are handled
correctly.
"""
# Prefill table with 7 rows written by 'master'
self._insert_rows("master", 7)
id_gen = self._create_id_generator()
self.assertEqual(id_gen.get_positions(), {"master": 7})
self.assertEqual(id_gen.get_current_token("master"), 7)
# Try allocating a new ID gen and check that we only see position
# advanced after we leave the context manager.
async def _get_next_async():
with await id_gen.get_next() as stream_id:
self.assertEqual(stream_id, 8)
self.assertEqual(id_gen.get_positions(), {"master": 7})
self.assertEqual(id_gen.get_current_token("master"), 7)
self.get_success(_get_next_async())
self.assertEqual(id_gen.get_positions(), {"master": 8})
self.assertEqual(id_gen.get_current_token("master"), 8)
def test_multi_instance(self):
"""Test that reads and writes from multiple processes are handled
correctly.
"""
self._insert_rows("first", 3)
self._insert_rows("second", 4)
first_id_gen = self._create_id_generator("first")
second_id_gen = self._create_id_generator("second")
self.assertEqual(first_id_gen.get_positions(), {"first": 3, "second": 7})
self.assertEqual(first_id_gen.get_current_token("first"), 3)
self.assertEqual(first_id_gen.get_current_token("second"), 7)
# Try allocating a new ID gen and check that we only see position
# advanced after we leave the context manager.
async def _get_next_async():
with await first_id_gen.get_next() as stream_id:
self.assertEqual(stream_id, 8)
self.assertEqual(
first_id_gen.get_positions(), {"first": 3, "second": 7}
)
self.get_success(_get_next_async())
self.assertEqual(first_id_gen.get_positions(), {"first": 8, "second": 7})
# However the ID gen on the second instance won't have seen the update
self.assertEqual(second_id_gen.get_positions(), {"first": 3, "second": 7})
# ... but calling `get_next` on the second instance should give a unique
# stream ID
async def _get_next_async():
with await second_id_gen.get_next() as stream_id:
self.assertEqual(stream_id, 9)
self.assertEqual(
second_id_gen.get_positions(), {"first": 3, "second": 7}
)
self.get_success(_get_next_async())
self.assertEqual(second_id_gen.get_positions(), {"first": 3, "second": 9})
# If the second ID gen gets told about the first, it correctly updates
second_id_gen.advance("first", 8)
self.assertEqual(second_id_gen.get_positions(), {"first": 8, "second": 9})
def test_get_next_txn(self):
"""Test that the `get_next_txn` function works correctly.
"""
# Prefill table with 7 rows written by 'master'
self._insert_rows("master", 7)
id_gen = self._create_id_generator()
self.assertEqual(id_gen.get_positions(), {"master": 7})
self.assertEqual(id_gen.get_current_token("master"), 7)
# Try allocating a new ID gen and check that we only see position
# advanced after we leave the context manager.
def _get_next_txn(txn):
stream_id = id_gen.get_next_txn(txn)
self.assertEqual(stream_id, 8)
self.assertEqual(id_gen.get_positions(), {"master": 7})
self.assertEqual(id_gen.get_current_token("master"), 7)
self.get_success(self.db.runInteraction("test", _get_next_txn))
self.assertEqual(id_gen.get_positions(), {"master": 8})
self.assertEqual(id_gen.get_current_token("master"), 8)

1
tox.ini
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@ -203,6 +203,7 @@ commands = mypy \
synapse/storage/data_stores/main/ui_auth.py \
synapse/storage/database.py \
synapse/storage/engines \
synapse/storage/util \
synapse/streams \
synapse/util/caches/stream_change_cache.py \
tests/replication/tcp/streams \