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# Copyright 2021 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.
import logging
from typing import TYPE_CHECKING, Any, Optional
from prometheus_client import Counter, Histogram
from synapse.logging.context import make_deferred_yieldable
from synapse.util import json_decoder, json_encoder
if TYPE_CHECKING:
from synapse.server import HomeServer
set_counter = Counter(
"synapse_external_cache_set",
"Number of times we set a cache",
labelnames=["cache_name"],
)
get_counter = Counter(
"synapse_external_cache_get",
"Number of times we get a cache",
labelnames=["cache_name", "hit"],
)
response_timer = Histogram(
"synapse_external_cache_response_time_seconds",
"Time taken to get a response from Redis for a cache get/set request",
labelnames=["method"],
buckets=(
0.001,
0.002,
0.005,
0.01,
0.02,
0.05,
),
)
logger = logging.getLogger(__name__)
class ExternalCache:
"""A cache backed by an external Redis. Does nothing if no Redis is
configured.
"""
def __init__(self, hs: "HomeServer"):
self._redis_connection = hs.get_outbound_redis_connection()
def _get_redis_key(self, cache_name: str, key: str) -> str:
return "cache_v1:%s:%s" % (cache_name, key)
def is_enabled(self) -> bool:
"""Whether the external cache is used or not.
It's safe to use the cache when this returns false, the methods will
just no-op, but the function is useful to avoid doing unnecessary work.
"""
return self._redis_connection is not None
async def set(self, cache_name: str, key: str, value: Any, expiry_ms: int) -> None:
"""Add the key/value to the named cache, with the expiry time given."""
if self._redis_connection is None:
return
set_counter.labels(cache_name).inc()
# txredisapi requires the value to be string, bytes or numbers, so we
# encode stuff in JSON.
encoded_value = json_encoder.encode(value)
logger.debug("Caching %s %s: %r", cache_name, key, encoded_value)
with response_timer.labels("set").time():
return await make_deferred_yieldable(
self._redis_connection.set(
self._get_redis_key(cache_name, key),
encoded_value,
pexpire=expiry_ms,
)
)
async def get(self, cache_name: str, key: str) -> Optional[Any]:
"""Look up a key/value in the named cache."""
if self._redis_connection is None:
return None
with response_timer.labels("get").time():
result = await make_deferred_yieldable(
self._redis_connection.get(self._get_redis_key(cache_name, key))
)
logger.debug("Got cache result %s %s: %r", cache_name, key, result)
get_counter.labels(cache_name, result is not None).inc()
if not result:
return None
# For some reason the integers get magically converted back to integers
if isinstance(result, int):
return result
return json_decoder.decode(result)
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