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Merge pull request #139 from matrix-org/bugs/SYN-369

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Fix race with cache invalidation. SYN-369
This commit is contained in:
Mark Haines 2015-05-05 17:46:13 +01:00
commit 31049c4d72
4 changed files with 80 additions and 16 deletions
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68
synapse/storage/_base.py
View File

@ -31,7 +31,9 @@ import functools
import simplejson as json
import sys
import time
import threading
DEBUG_CACHES = False
logger = logging.getLogger(__name__)
@ -68,9 +70,20 @@ class Cache(object):
self.name = name
self.keylen = keylen
self.sequence = 0
self.thread = None
caches_by_name[name] = self.cache
def check_thread(self):
expected_thread = self.thread
if expected_thread is None:
self.thread = threading.current_thread()
else:
if expected_thread is not threading.current_thread():
raise ValueError(
"Cache objects can only be accessed from the main thread"
)
def get(self, *keyargs):
if len(keyargs) != self.keylen:
raise ValueError("Expected a key to have %d items", self.keylen)
@ -82,6 +95,13 @@ class Cache(object):
cache_counter.inc_misses(self.name)
raise KeyError()
def update(self, sequence, *args):
self.check_thread()
if self.sequence == sequence:
# Only update the cache if the caches sequence number matches the
# number that the cache had before the SELECT was started (SYN-369)
self.prefill(*args)
def prefill(self, *args): # because I can't *keyargs, value
keyargs = args[:-1]
value = args[-1]
@ -96,9 +116,12 @@ class Cache(object):
self.cache[keyargs] = value
def invalidate(self, *keyargs):
self.check_thread()
if len(keyargs) != self.keylen:
raise ValueError("Expected a key to have %d items", self.keylen)
# Increment the sequence number so that any SELECT statements that
# raced with the INSERT don't update the cache (SYN-369)
self.sequence += 1
self.cache.pop(keyargs, None)
@ -128,11 +151,26 @@ def cached(max_entries=1000, num_args=1, lru=False):
@defer.inlineCallbacks
def wrapped(self, *keyargs):
try:
defer.returnValue(cache.get(*keyargs))
cached_result = cache.get(*keyargs)
if DEBUG_CACHES:
actual_result = yield orig(self, *keyargs)
if actual_result != cached_result:
logger.error(
"Stale cache entry %s%r: cached: %r, actual %r",
orig.__name__, keyargs,
cached_result, actual_result,
)
raise ValueError("Stale cache entry")
defer.returnValue(cached_result)
except KeyError:
# Get the sequence number of the cache before reading from the
# database so that we can tell if the cache is invalidated
# while the SELECT is executing (SYN-369)
sequence = cache.sequence
ret = yield orig(self, *keyargs)
cache.prefill(*keyargs + (ret,))
cache.update(sequence, *keyargs + (ret,))
defer.returnValue(ret)
@ -147,12 +185,20 @@ class LoggingTransaction(object):
"""An object that almost-transparently proxies for the 'txn' object
passed to the constructor. Adds logging and metrics to the .execute()
method."""
__slots__ = ["txn", "name", "database_engine"]
__slots__ = ["txn", "name", "database_engine", "after_callbacks"]
def __init__(self, txn, name, database_engine):
def __init__(self, txn, name, database_engine, after_callbacks):
object.__setattr__(self, "txn", txn)
object.__setattr__(self, "name", name)
object.__setattr__(self, "database_engine", database_engine)
object.__setattr__(self, "after_callbacks", after_callbacks)
def call_after(self, callback, *args):
"""Call the given callback on the main twisted thread after the
transaction has finished. Used to invalidate the caches on the
correct thread.
"""
self.after_callbacks.append((callback, args))
def __getattr__(self, name):
return getattr(self.txn, name)
@ -294,6 +340,8 @@ class SQLBaseStore(object):
start_time = time.time() * 1000
after_callbacks = []
def inner_func(conn, *args, **kwargs):
with LoggingContext("runInteraction") as context:
if self.database_engine.is_connection_closed(conn):
@ -318,10 +366,10 @@ class SQLBaseStore(object):
while True:
try:
txn = conn.cursor()
return func(
LoggingTransaction(txn, name, self.database_engine),
*args, **kwargs
txn = LoggingTransaction(
txn, name, self.database_engine, after_callbacks
)
return func(txn, *args, **kwargs)
except self.database_engine.module.OperationalError as e:
# This can happen if the database disappears mid
# transaction.
@ -370,6 +418,8 @@ class SQLBaseStore(object):
result = yield self._db_pool.runWithConnection(
inner_func, *args, **kwargs
)
for after_callback, after_args in after_callbacks:
after_callback(*after_args)
defer.returnValue(result)
def cursor_to_dict(self, cursor):

4
synapse/storage/event_federation.py
View File

@ -330,7 +330,9 @@ class EventFederationStore(SQLBaseStore):
)
txn.execute(query)
self.get_latest_event_ids_in_room.invalidate(room_id)
txn.call_after(
self.get_latest_event_ids_in_room.invalidate, room_id
)
def get_backfill_events(self, room_id, event_list, limit):
"""Get a list of Events for a given topic that occurred before (and

20
synapse/storage/events.py
View File

@ -93,7 +93,7 @@ class EventsStore(SQLBaseStore):
current_state=None):
# Remove the any existing cache entries for the event_id
self._invalidate_get_event_cache(event.event_id)
txn.call_after(self._invalidate_get_event_cache, event.event_id)
if stream_ordering is None:
with self._stream_id_gen.get_next_txn(txn) as stream_ordering:
@ -114,6 +114,13 @@ class EventsStore(SQLBaseStore):
)
for s in current_state:
if s.type == EventTypes.Member:
txn.call_after(
self.get_rooms_for_user.invalidate, s.state_key
)
txn.call_after(
self.get_joined_hosts_for_room.invalidate, s.room_id
)
self._simple_insert_txn(
txn,
"current_state_events",
@ -281,7 +288,9 @@ class EventsStore(SQLBaseStore):
)
if context.rejected:
self._store_rejections_txn(txn, event.event_id, context.rejected)
self._store_rejections_txn(
txn, event.event_id, context.rejected
)
for hash_alg, hash_base64 in event.hashes.items():
hash_bytes = decode_base64(hash_base64)
@ -293,7 +302,8 @@ class EventsStore(SQLBaseStore):
for alg, hash_base64 in prev_hashes.items():
hash_bytes = decode_base64(hash_base64)
self._store_prev_event_hash_txn(
txn, event.event_id, prev_event_id, alg, hash_bytes
txn, event.event_id, prev_event_id, alg,
hash_bytes
)
for auth_id, _ in event.auth_events:
@ -356,9 +366,11 @@ class EventsStore(SQLBaseStore):
}
)
return
def _store_redaction(self, txn, event):
# invalidate the cache for the redacted event
self._invalidate_get_event_cache(event.redacts)
txn.call_after(self._invalidate_get_event_cache, event.redacts)
txn.execute(
"INSERT INTO redactions (event_id, redacts) VALUES (?,?)",
(event.event_id, event.redacts)

4
synapse/storage/roommember.py
View File

@ -64,8 +64,8 @@ class RoomMemberStore(SQLBaseStore):
}
)
self.get_rooms_for_user.invalidate(target_user_id)
self.get_joined_hosts_for_room.invalidate(event.room_id)
txn.call_after(self.get_rooms_for_user.invalidate, target_user_id)
txn.call_after(self.get_joined_hosts_for_room.invalidate, event.room_id)
def get_room_member(self, user_id, room_id):
"""Retrieve the current state of a room member.