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Limit the size of the HomeServerConfig cache in trial test runs #15646

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Limit the size of the HomeServerConfig cache in trial test runs #15646

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1 change: 1 addition & 0 deletions changelog.d/15646.misc
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Limit the size of the `HomeServerConfig` cache in trial test runs.
23 changes: 7 additions & 16 deletions tests/unittest.py
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Expand Up @@ -13,6 +13,7 @@
# 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 functools
import gc
import hashlib
import hmac
Expand Down Expand Up @@ -150,7 +151,11 @@ def deepcopy_config(config: _TConfig) -> _TConfig:
return new_config


_make_homeserver_config_obj_cache: Dict[str, Union[RootConfig, Config]] = {}
@functools.lru_cache(maxsize=8)
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Is there anyway to know how many of these actually get re-used?

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There are actually 359 distinct configs used in tests, not 80 as I had written.
With a size of 8, the LRU cache reports CacheInfo(hits=1676, misses=380, maxsize=8, currsize=8).
With an unlimited size, the LRU cache reports CacheInfo(hits=1697, misses=359, maxsize=None, currsize=359).

The histogram of config usage looks like
1249, 57, 33, 30, 20, 20, 19, 16, 14, 13, 12, 12, 11, 11, 11, 10, 9, 8,
8, 8, 8, 7, 6, 6, 6, 6, 6, 5, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
... followed by a long tail of ones.

There's one main config that's used by most tests and then some others.

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Seems like 8 is a reasonable size then. 😄

def _parse_config_dict(config: str) -> RootConfig:
config_obj = HomeServerConfig()
config_obj.parse_config_dict(json.loads(config), "", "")
return config_obj


def make_homeserver_config_obj(config: Dict[str, Any]) -> RootConfig:
Expand All @@ -164,21 +169,7 @@ def make_homeserver_config_obj(config: Dict[str, Any]) -> RootConfig:
but it keeps a cache of `HomeServerConfig` instances and deepcopies them as needed,
to avoid validating the whole configuration every time.
"""
cache_key = json.dumps(config)

if cache_key in _make_homeserver_config_obj_cache:
# Cache hit: reuse the existing instance
config_obj = _make_homeserver_config_obj_cache[cache_key]
else:
# Cache miss; create the actual instance
config_obj = HomeServerConfig()
config_obj.parse_config_dict(config, "", "")

# Add to the cache
_make_homeserver_config_obj_cache[cache_key] = config_obj

assert isinstance(config_obj, RootConfig)

config_obj = _parse_config_dict(json.dumps(config, sort_keys=True))
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Freezing the config dict into an immutabledict was over twice as slow as JSON serialization when I tested it. And created problems with the config parsing, because all our type checks expect lists instead of tuples and dicts instead of immutabledicts.

return deepcopy_config(config_obj)


Expand Down