diff options
Diffstat (limited to 'synapse')
| -rw-r--r-- | synapse/storage/util/id_generators.py | 169 |
1 files changed, 167 insertions, 2 deletions
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py index 9d851beaa5..86d04ea9ac 100644 --- a/synapse/storage/util/id_generators.py +++ b/synapse/storage/util/id_generators.py @@ -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) + ) |