fix: remove extra redis calls (#125)

- cache server version
- check the new hash name first

Author: ville

src/corva/cache_adapter.py

@@ -53,13 +53,17 @@ def delete_all(self) -> None:
 class HashMigrator:
     MINIMUM_ALLOWED_REDIS_SERVER = semver.Version(major=7, minor=4, patch=0)
     NEW_HASH_PREFIX = "migrated/"
+    _version_checked: bool = False
 
     def __init__(self, hash_name: str, client: redis.Redis):
         self.hash_name = hash_name
         self.zset_name = f"{hash_name}.EXPIREAT"
         self.client = client
 
     def check_redis_server_version(self) -> None:
+        if HashMigrator._version_checked:
+            return
+
         # Require Redis 7.4+ for per-field TTL commands
         redis_version_str = self.client.info(section="server")["redis_version"]
         server_version = semver.Version.parse(version=redis_version_str)
@@ -72,6 +76,8 @@ def check_redis_server_version(self) -> None:
                 f"less then {self.MINIMUM_ALLOWED_REDIS_SERVER} -> "
                 f"incompatible with used python SDK version `{version('corva-sdk')}`")
 
+        HashMigrator._version_checked = True
+
     def run(self) -> bool:
         """Prepare parallel new-style cache while keeping legacy structures.
 
@@ -91,16 +97,16 @@ def run(self) -> bool:
 
         from corva import Logger
 
-        # Legacy structure must exist; otherwise nothing to do
-        if not self.client.exists(self.zset_name):
-            return False
-
         new_hash_name = self.NEW_HASH_PREFIX + self.hash_name
 
         # If new hash already exists, consider migration already done
         if self.client.exists(new_hash_name):
             return False
 
+        # Legacy structure must exist; otherwise nothing to do
+        if not self.client.exists(self.zset_name):
+            return False
+
         # Current server time in ms
         sec, micro = self.client.time()
         now_ms = int(sec) * 1000 + int(micro) // 1000

tests/integration/test_cache_migration.py

@@ -17,6 +17,7 @@ def current_redis_server_time(redis_client):
 
 
 def test_server_version_incompatible_with_sdk(redis_client):
+    HashMigrator._version_checked = False
 
     with (pytest.raises(RuntimeError) as exc):
         with mock.patch.object(redis_client, "info",