From a67b00d7c72852c97691676c66fbaa5015007525 Mon Sep 17 00:00:00 2001
From: Igor Lins e Silva <4753812+igorls@users.noreply.github.com>
Date: Tue, 7 Apr 2026 17:19:53 -0300
Subject: [PATCH 1/2] perf: cache ChromaDB PersistentClient instead of
 re-instantiating per call

The MCP server previously created a new PersistentClient on every tool
call via _get_collection(). This incurs HNSW index loading overhead
on each request.

Cache the client and collection at module level. The cache resets
naturally on process restart (MCP runs as a subprocess).

Also adds a _reset_mcp_cache fixture to conftest.py for test isolation.

Includes test infrastructure from PR #131.
92 tests pass.
---
 mempalace/mcp_server.py | 16 ++++++++++++----
 tests/conftest.py       | 13 +++++++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/mempalace/mcp_server.py b/mempalace/mcp_server.py
index 2169255..81c9b50 100644
--- a/mempalace/mcp_server.py
+++ b/mempalace/mcp_server.py
@@ -39,13 +39,21 @@ logger = logging.getLogger("mempalace_mcp")
 _config = MempalaceConfig()
 
 
+_client_cache = None
+_collection_cache = None
+
+
 def _get_collection(create=False):
-    """Return the ChromaDB collection, or None on failure."""
+    """Return the ChromaDB collection, caching the client between calls."""
+    global _client_cache, _collection_cache
     try:
-        client = chromadb.PersistentClient(path=_config.palace_path)
+        if _client_cache is None:
+            _client_cache = chromadb.PersistentClient(path=_config.palace_path)
         if create:
-            return client.get_or_create_collection(_config.collection_name)
-        return client.get_collection(_config.collection_name)
+            _collection_cache = _client_cache.get_or_create_collection(_config.collection_name)
+        elif _collection_cache is None:
+            _collection_cache = _client_cache.get_collection(_config.collection_name)
+        return _collection_cache
     except Exception:
         return None
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 22b5e42..fa08802 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -34,6 +34,19 @@ from mempalace.config import MempalaceConfig  # noqa: E402
 from mempalace.knowledge_graph import KnowledgeGraph  # noqa: E402
 
 
+@pytest.fixture(autouse=True)
+def _reset_mcp_cache():
+    """Reset the MCP server's cached ChromaDB client/collection between tests."""
+    yield
+    try:
+        from mempalace import mcp_server
+
+        mcp_server._client_cache = None
+        mcp_server._collection_cache = None
+    except (ImportError, AttributeError):
+        pass
+
+
 @pytest.fixture(scope="session", autouse=True)
 def _isolate_home():
     """Ensure HOME points to a temp dir for the entire test session.

From 47696bef8c28adae9288af792468923bcb45adf5 Mon Sep 17 00:00:00 2001
From: Igor Lins e Silva <4753812+igorls@users.noreply.github.com>
Date: Tue, 7 Apr 2026 17:29:12 -0300
Subject: [PATCH 2/2] =?UTF-8?q?fix:=20address=20Copilot=20review=20?=
 =?UTF-8?q?=E2=80=94=20derive=20MCP=20version,=20improve=20test=20isolatio?=
 =?UTF-8?q?n=20and=20portability?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 tests/conftest.py        | 19 ++++++++++++-------
 tests/test_mcp_server.py |  7 ++++---
 tests/test_searcher.py   |  4 ++--
 3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/tests/conftest.py b/tests/conftest.py
index fa08802..eb2b432 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -37,14 +37,19 @@ from mempalace.knowledge_graph import KnowledgeGraph  # noqa: E402
 @pytest.fixture(autouse=True)
 def _reset_mcp_cache():
     """Reset the MCP server's cached ChromaDB client/collection between tests."""
-    yield
-    try:
-        from mempalace import mcp_server
 
-        mcp_server._client_cache = None
-        mcp_server._collection_cache = None
-    except (ImportError, AttributeError):
-        pass
+    def _clear_cache():
+        try:
+            from mempalace import mcp_server
+
+            mcp_server._client_cache = None
+            mcp_server._collection_cache = None
+        except (ImportError, AttributeError):
+            pass
+
+    _clear_cache()
+    yield
+    _clear_cache()
 
 
 @pytest.fixture(scope="session", autouse=True)
diff --git a/tests/test_mcp_server.py b/tests/test_mcp_server.py
index cf37a27..09a3c46 100644
--- a/tests/test_mcp_server.py
+++ b/tests/test_mcp_server.py
@@ -151,9 +151,10 @@ class TestReadTools:
         assert result["taxonomy"]["project"]["frontend"] == 1
         assert result["taxonomy"]["notes"]["planning"] == 1
 
-    def test_no_palace_returns_error(self, monkeypatch, config, kg):
-        config._file_config["palace_path"] = "/nonexistent/path"
-        _patch_mcp_server(monkeypatch, config, "/nonexistent/path", kg)
+    def test_no_palace_returns_error(self, monkeypatch, config, kg, tmp_path):
+        missing = str(tmp_path / "missing")
+        config._file_config["palace_path"] = missing
+        _patch_mcp_server(monkeypatch, config, missing, kg)
         from mempalace.mcp_server import tool_status
 
         result = tool_status()
diff --git a/tests/test_searcher.py b/tests/test_searcher.py
index 44a05aa..1c2687d 100644
--- a/tests/test_searcher.py
+++ b/tests/test_searcher.py
@@ -30,8 +30,8 @@ class TestSearchMemories:
         result = search_memories("code", palace_path, n_results=2)
         assert len(result["results"]) <= 2
 
-    def test_no_palace_returns_error(self):
-        result = search_memories("anything", "/nonexistent/path")
+    def test_no_palace_returns_error(self, tmp_path):
+        result = search_memories("anything", str(tmp_path / "missing"))
         assert "error" in result
 
     def test_result_fields(self, palace_path, seeded_collection):