cache: Use zstd compression level 9 for bmemcached compression.

tools/test-backend

@@ -104,6 +104,7 @@ not_yet_fully_covered = [
     "zerver/lib/test_fixtures.py",
     "zerver/lib/test_runner.py",
     "zerver/lib/test_console_output.py",
+    "zerver/lib/zstd_level9.py",
     "zerver/openapi/curl_param_value_generators.py",
     "zerver/openapi/javascript_examples.py",
     "zerver/openapi/python_examples.py",

zerver/lib/singleton_bmemcached.py

@@ -2,14 +2,15 @@ import pickle
 from functools import lru_cache
 from typing import Any
 
-import zstd
 from django_bmemcached.memcached import BMemcached
 
+from zerver.lib import zstd_level9
+
 
 @lru_cache(None)
 def _get_bmemcached(location: str, param_bytes: bytes) -> BMemcached:
     params = pickle.loads(param_bytes)  # noqa: S301
-    params["OPTIONS"]["compression"] = zstd
+    params["OPTIONS"]["compression"] = zstd_level9
     return BMemcached(location, params)
 
 

zerver/lib/zstd_level9.py

@@ -0,0 +1,10 @@
+from zstd import compress as original_compress
+from zstd import decompress
+
+__all__ = ["compress", "decompress"]
+
+
+def compress(data: bytes, level: int | None = None) -> bytes:
+    if level is None:
+        level = 9
+    return original_compress(data, level)