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
# 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]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
def __init__(
self,
db_conn,
db: DatabasePool,
instance_name: str,
table: str,
instance_column: str,
id_column: str,
sequence_name: str,
positive: bool = True,
):
self._db = db
self._instance_name = instance_name
self._positive = positive
self._return_factor = 1 if positive else -1
# We lock as some functions may be called from DB threads.
self._lock = threading.Lock()
# Note: If we are a negative stream then we still store all the IDs as
# positive to make life easier for us, and simply negate the IDs when we
# return them.
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]
# We track the max position where we know everything before has been
# persisted. This is done by a) looking at the min across all instances
# and b) noting that if we have seen a run of persisted positions
# without gaps (e.g. 5, 6, 7) then we can skip forward (e.g. to 7).
#
# Note: There is no guarentee that the IDs generated by the sequence
# will be gapless; gaps can form when e.g. a transaction was rolled
# back. This means that sometimes we won't be able to skip forward the
# position even though everything has been persisted. However, since
# gaps should be relatively rare it's still worth doing the book keeping
# that allows us to skip forwards when there are gapless runs of
# positions.
self._persisted_upto_position = (min(self._current_positions.values())
if self._current_positions else 0)
self._known_persisted_positions = [] # type: List[int]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
def __init__(
self,
db_conn,
db: DatabasePool,
stream_name: str,
instance_name: str,
tables: List[Tuple[str, str, str]],
sequence_name: str,
writers: List[str],
positive: bool = True,
):
self._db = db
self._stream_name = stream_name
self._instance_name = instance_name
self._positive = positive
self._writers = writers
self._return_factor = 1 if positive else -1
# We lock as some functions may be called from DB threads.
self._lock = threading.Lock()
# Note: If we are a negative stream then we still store all the IDs as
# positive to make life easier for us, and simply negate the IDs when we
# return them.
self._current_positions = {} # type: Dict[str, int]
# 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]
# Set of local IDs that we've processed that are larger than the current
# position, due to there being smaller unpersisted IDs.
self._finished_ids = set() # type: Set[int]
# We track the max position where we know everything before has been
# persisted. This is done by a) looking at the min across all instances
# and b) noting that if we have seen a run of persisted positions
# without gaps (e.g. 5, 6, 7) then we can skip forward (e.g. to 7).
#
# Note: There is no guarantee that the IDs generated by the sequence
# will be gapless; gaps can form when e.g. a transaction was rolled
# back. This means that sometimes we won't be able to skip forward the
# position even though everything has been persisted. However, since
# gaps should be relatively rare it's still worth doing the book keeping
# that allows us to skip forwards when there are gapless runs of
# positions.
#
# We start at 1 here as a) the first generated stream ID will be 2, and
# b) other parts of the code assume that stream IDs are strictly greater
# than 0.
self._persisted_upto_position = (min(self._current_positions.values())
if self._current_positions else 1)
self._known_persisted_positions = [] # type: List[int]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
# We check that the table and sequence haven't diverged.
for table, _, id_column in tables:
self._sequence_gen.check_consistency(
db_conn,
table=table,
id_column=id_column,
stream_name=stream_name,
positive=positive,
)
# This goes and fills out the above state from the database.
self._load_current_ids(db_conn, tables)
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
stream_name: A name for the stream, for use in the `stream_positions`
table. (Does not need to be the same as the replication stream name)
instance_name: The name of this instance.
tables: List of tables associated with the stream. Tuple of table
name, column name that stores the writer's instance name, and
column name that stores the stream ID.
sequence_name: The name of the postgres sequence used to generate new
IDs.
writers: A list of known writers to use to populate current positions
on startup. Can be empty if nothing uses `get_current_token` or
`get_positions` (e.g. caches stream).
positive: Whether the IDs are positive (true) or negative (false).
When using negative IDs we go backwards from -1 to -2, -3, etc.
"""
def __init__(
self,
db_conn,
db: DatabasePool,
stream_name: str,
instance_name: str,
tables: List[Tuple[str, str, str]],
sequence_name: str,
writers: List[str],
positive: bool = True,
):
self._db = db
self._stream_name = stream_name
self._instance_name = instance_name
self._positive = positive
self._writers = writers
self._return_factor = 1 if positive else -1
# We lock as some functions may be called from DB threads.
self._lock = threading.Lock()
# Note: If we are a negative stream then we still store all the IDs as
# positive to make life easier for us, and simply negate the IDs when we
# return them.
self._current_positions = {} # type: Dict[str, int]
# 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]
# Set of local IDs that we've processed that are larger than the current
# position, due to there being smaller unpersisted IDs.
self._finished_ids = set() # type: Set[int]
# We track the max position where we know everything before has been
# persisted. This is done by a) looking at the min across all instances
# and b) noting that if we have seen a run of persisted positions
# without gaps (e.g. 5, 6, 7) then we can skip forward (e.g. to 7).
#
# Note: There is no guarantee that the IDs generated by the sequence
# will be gapless; gaps can form when e.g. a transaction was rolled
# back. This means that sometimes we won't be able to skip forward the
# position even though everything has been persisted. However, since
# gaps should be relatively rare it's still worth doing the book keeping
# that allows us to skip forwards when there are gapless runs of
# positions.
#
# We start at 1 here as a) the first generated stream ID will be 2, and
# b) other parts of the code assume that stream IDs are strictly greater
# than 0.
self._persisted_upto_position = (min(self._current_positions.values())
if self._current_positions else 1)
self._known_persisted_positions = [] # type: List[int]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
# We check that the table and sequence haven't diverged.
for table, _, id_column in tables:
self._sequence_gen.check_consistency(
db_conn,
table=table,
id_column=id_column,
stream_name=stream_name,
positive=positive,
)
# This goes and fills out the above state from the database.
self._load_current_ids(db_conn, tables)
def _load_current_ids(
self,
db_conn,
tables: List[Tuple[str, str, str]],
):
cur = db_conn.cursor(txn_name="_load_current_ids")
# Load the current positions of all writers for the stream.
if self._writers:
# We delete any stale entries in the positions table. This is
# important if we add back a writer after a long time; we want to
# consider that a "new" writer, rather than using the old stale
# entry here.
sql = """
DELETE FROM stream_positions
WHERE
stream_name = ?
AND instance_name != ALL(?)
"""
cur.execute(sql, (self._stream_name, self._writers))
sql = """
SELECT instance_name, stream_id FROM stream_positions
WHERE stream_name = ?
"""
cur.execute(sql, (self._stream_name, ))
self._current_positions = {
instance: stream_id * self._return_factor
for instance, stream_id in cur if instance in self._writers
}
# We set the `_persisted_upto_position` to be the minimum of all current
# positions. If empty we use the max stream ID from the DB table.
min_stream_id = min(self._current_positions.values(), default=None)
if min_stream_id is None:
# We add a GREATEST here to ensure that the result is always
# positive. (This can be a problem for e.g. backfill streams where
# the server has never backfilled).
max_stream_id = 1
for table, _, id_column in tables:
sql = """
SELECT GREATEST(COALESCE(%(agg)s(%(id)s), 1), 1)
FROM %(table)s
""" % {
"id": id_column,
"table": table,
"agg": "MAX" if self._positive else "-MIN",
}
cur.execute(sql)
(stream_id, ) = cur.fetchone()
max_stream_id = max(max_stream_id, stream_id)
self._persisted_upto_position = max_stream_id
else:
# If we have a min_stream_id then we pull out everything greater
# than it from the DB so that we can prefill
# `_known_persisted_positions` and get a more accurate
# `_persisted_upto_position`.
#
# We also check if any of the later rows are from this instance, in
# which case we use that for this instance's current position. This
# is to handle the case where we didn't finish persisting to the
# stream positions table before restart (or the stream position
# table otherwise got out of date).
self._persisted_upto_position = min_stream_id
rows = []
for table, instance_column, id_column in tables:
sql = """
SELECT %(instance)s, %(id)s FROM %(table)s
WHERE ? %(cmp)s %(id)s
""" % {
"id": id_column,
"table": table,
"instance": instance_column,
"cmp": "<=" if self._positive else ">=",
}
cur.execute(sql, (min_stream_id * self._return_factor, ))
rows.extend(cur)
# Sort so that we handle rows in order for each instance.
rows.sort()
with self._lock:
for (
instance,
stream_id,
) in rows:
stream_id = self._return_factor * stream_id
self._add_persisted_position(stream_id)
if instance == self._instance_name:
self._current_positions[instance] = stream_id
cur.close()
def _load_next_id_txn(self, txn) -> int:
return self._sequence_gen.get_next_id_txn(txn)
def _load_next_mult_id_txn(self, txn, n: int) -> List[int]:
return self._sequence_gen.get_next_mult_txn(txn, n)
def get_next(self):
"""
Usage:
async with stream_id_gen.get_next() as stream_id:
# ... persist event ...
"""
return _MultiWriterCtxManager(self)
def get_next_mult(self, n: int):
"""
Usage:
async with stream_id_gen.get_next_mult(5) as stream_ids:
# ... persist events ...
"""
return _MultiWriterCtxManager(self, n)
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)
# 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):
"""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 = None # type: Optional[int]
if self._unfinished_ids:
# If there are unfinished IDs then the new position will be the
# largest finished ID less than the minimum unfinished ID.
finished = set()
min_unfinshed = min(self._unfinished_ids)
for s in self._finished_ids:
if s < min_unfinshed:
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:
"""Returns the maximum stream id such that all stream ids less than or
equal to it have been successfully persisted.
"""
return self.get_persisted_upto_position()
def get_current_token_for_writer(self, instance_name: str) -> int:
"""Returns the position of the given writer."""
# 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):
"""Advance the position of the named writer to the given ID, if greater
than existing entry.
"""
new_id *= self._return_factor
with self._lock:
self._current_positions[instance_name] = max(
new_id, self._current_positions.get(instance_name, 0))
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):
"""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))
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
# 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]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
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):
return self._sequence_gen.get_next_id_txn(txn)
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)
)
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.
positive: Whether the IDs are positive (true) or negative (false).
When using negative IDs we go backwards from -1 to -2, -3, etc.
"""
def __init__(
self,
db_conn,
db: DatabasePool,
instance_name: str,
table: str,
instance_column: str,
id_column: str,
sequence_name: str,
positive: bool = True,
):
self._db = db
self._instance_name = instance_name
self._positive = positive
self._return_factor = 1 if positive else -1
# We lock as some functions may be called from DB threads.
self._lock = threading.Lock()
# Note: If we are a negative stream then we still store all the IDs as
# positive to make life easier for us, and simply negate the IDs when we
# return them.
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]
# We track the max position where we know everything before has been
# persisted. This is done by a) looking at the min across all instances
# and b) noting that if we have seen a run of persisted positions
# without gaps (e.g. 5, 6, 7) then we can skip forward (e.g. to 7).
#
# Note: There is no guarentee that the IDs generated by the sequence
# will be gapless; gaps can form when e.g. a transaction was rolled
# back. This means that sometimes we won't be able to skip forward the
# position even though everything has been persisted. However, since
# gaps should be relatively rare it's still worth doing the book keeping
# that allows us to skip forwards when there are gapless runs of
# positions.
self._persisted_upto_position = (min(self._current_positions.values())
if self._current_positions else 0)
self._known_persisted_positions = [] # type: List[int]
self._sequence_gen = PostgresSequenceGenerator(sequence_name)
def _load_current_ids(self, db_conn, table: str, instance_column: str,
id_column: str) -> Dict[str, int]:
# If positive stream aggregate via MAX. For negative stream use MIN
# *and* negate the result to get a positive number.
sql = """
SELECT %(instance)s, %(agg)s(%(id)s) FROM %(table)s
GROUP BY %(instance)s
""" % {
"instance": instance_column,
"id": id_column,
"table": table,
"agg": "MAX" if self._positive else "-MIN",
}
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) -> int:
return self._sequence_gen.get_next_id_txn(txn)
def _load_next_mult_id_txn(self, txn, n: int) -> List[int]:
return self._sequence_gen.get_next_mult_txn(txn, n)
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.
with self._lock:
assert self._current_positions.get(self._instance_name,
0) < next_id
self._unfinished_ids.add(next_id)
@contextlib.contextmanager
def manager():
try:
# Multiply by the return factor so that the ID has correct sign.
yield self._return_factor * next_id
finally:
self._mark_id_as_finished(next_id)
return manager()
async def get_next_mult(self, n: int):
"""
Usage:
with await stream_id_gen.get_next_mult(5) as stream_ids:
# ... persist events ...
"""
next_ids = await self._db.runInteraction("_load_next_mult_id",
self._load_next_mult_id_txn,
n)
# Assert the fetched ID is actually greater than any ID we've already
# seen. If not, then the sequence and table have got out of sync
# somehow.
with self._lock:
assert max(self._current_positions.values(),
default=0) < min(next_ids)
self._unfinished_ids.update(next_ids)
@contextlib.contextmanager
def manager():
try:
yield [self._return_factor * i for i in next_ids]
finally:
for i in next_ids:
self._mark_id_as_finished(i)
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 self._return_factor * 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)
self._add_persisted_position(next_id)
def get_current_token(self) -> int:
"""Returns the maximum stream id such that all stream ids less than or
equal to it have been successfully persisted.
"""
# Currently we don't support this operation, as it's not obvious how to
# condense the stream positions of multiple writers into a single int.
raise NotImplementedError()
def get_current_token_for_writer(self, instance_name: str) -> int:
"""Returns the position of the given writer.
"""
with self._lock:
return self._return_factor * 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 {
name: self._return_factor * i
for name, i in self._current_positions.items()
}
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.
"""
new_id *= self._return_factor
with self._lock:
self._current_positions[instance_name] = max(
new_id, self._current_positions.get(instance_name, 0))
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):
"""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)
# 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())
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
