fix(chroma): split get_or_create_collection to prevent reopen SIGSEGV (upstream MemPalace#1262)

Author: Scorpion

mempalace/backends/chroma.py

@@ -8,6 +8,7 @@
 from typing import Any, Optional
 
 import chromadb
+from chromadb.errors import NotFoundError as _ChromaNotFoundError
 
 from .base import (
     BaseBackend,
@@ -759,13 +760,19 @@ def get_collection(
         ef_kwargs = {}
         if embedding_function is not None:
             ef_kwargs["embedding_function"] = embedding_function
-
         if create:
-            collection = client.get_or_create_collection(
-                collection_name,
-                metadata={"hnsw:space": hnsw_space, **_HNSW_BLOAT_GUARD},
-                **ef_kwargs,
-            )
+            try:
+                collection = client.get_collection(collection_name, **ef_kwargs)
+            except _ChromaNotFoundError:
+                collection = client.create_collection(
+                    collection_name,
+                    metadata={
+                        "hnsw:space": hnsw_space,
+                        "hnsw:num_threads": 1,
+                        **_HNSW_BLOAT_GUARD,
+                    },
+                    **ef_kwargs,
+                )
         else:
             collection = client.get_collection(collection_name, **ef_kwargs)
         return ChromaCollection(

tests/test_backends.py

@@ -334,6 +334,68 @@ def test_chroma_backend_creates_collection_with_cosine_distance(tmp_path):
     assert col.metadata.get("hnsw:space") == "cosine"
 
 
+def test_chroma_backend_sets_hnsw_bloat_guard_on_creation(tmp_path):
+    """The HNSW guard from #344 must land on freshly-created collection metadata.
+
+    Without batch_size + sync_threshold, mining ~10K+ drawers triggers the
+    resize+persist drift that bloats link_lists.bin into hundreds of GB sparse
+    and segfaults `status` / `search` / `repair`. The guard belongs at
+    collection-creation time so every fresh palace gets it without needing
+    a runtime retrofit. Asserting both keys land on the persisted metadata
+    also covers the #1161 "config silently dropped" concern at CI time.
+    """
+    palace_path = tmp_path / "palace"
+
+    ChromaBackend().get_collection(
+        str(palace_path),
+        collection_name="mempalace_drawers",
+        create=True,
+    )
+
+    client = chromadb.PersistentClient(path=str(palace_path))
+    col = client.get_collection("mempalace_drawers")
+    assert col.metadata.get("hnsw:batch_size") == 50_000
+    assert col.metadata.get("hnsw:sync_threshold") == 50_000
+
+
+def test_chroma_backend_create_collection_sets_hnsw_bloat_guard(tmp_path):
+    """Same guard must apply via the legacy create_collection() path."""
+    palace_path = tmp_path / "palace"
+
+    ChromaBackend().create_collection(str(palace_path), "mempalace_drawers")
+
+    client = chromadb.PersistentClient(path=str(palace_path))
+    col = client.get_collection("mempalace_drawers")
+    assert col.metadata.get("hnsw:batch_size") == 50_000
+    assert col.metadata.get("hnsw:sync_threshold") == 50_000
+
+
+def test_get_collection_create_true_is_idempotent(tmp_path):
+    """Calling get_collection(create=True) twice on the same name must not crash.
+
+    ChromaDB 1.5.x's Rust bindings SIGSEGV when get_or_create_collection is
+    called with metadata that differs from the stored collection metadata. The
+    fix splits the call into get_collection -> fallback create_collection so the
+    metadata-comparison codepath in chromadb_rust_bindings is never reached for
+    existing collections. Regression guard for issue #1089.
+    """
+    palace = str(tmp_path / "palace")
+    backend = ChromaBackend()
+    backend.get_collection(palace, collection_name="mempalace_drawers", create=True)
+    col2 = backend.get_collection(palace, collection_name="mempalace_drawers", create=True)
+    assert isinstance(col2, ChromaCollection)
+
+
+def test_get_collection_create_true_preserves_existing_metadata(tmp_path):
+    """Existing collection metadata is not overwritten when reopened with create=True."""
+    palace = str(tmp_path / "palace")
+    backend = ChromaBackend()
+    backend.get_collection(palace, collection_name="mempalace_drawers", create=True)
+    col = backend.get_collection(palace, collection_name="mempalace_drawers", create=True)
+    assert col._collection.metadata["hnsw:space"] == "cosine"
+    assert col._collection.metadata.get("hnsw:batch_size") == 50_000
+
+
 def test_fix_blob_seq_ids_converts_blobs_to_integers(tmp_path):
     """Simulate a ChromaDB 0.6.x database with BLOB seq_ids and verify repair."""
     db_path = tmp_path / "chroma.sqlite3"