chore: Updating chunk id generation to ensure uniqueness (#2618)

# What does this PR do?
This handles an edge case for `generate_chunk_id` if the concatenation
of the `document_id` and `chunk_text` combination are not unique. Adding
the window location ensures uniqueness.

## Test Plan
Added unit test

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

llama_stack/providers/utils/memory/vector_store.py

@@ -164,7 +164,8 @@ def make_overlapped_chunks(
     for i in range(0, len(tokens), window_len - overlap_len):
         toks = tokens[i : i + window_len]
         chunk = tokenizer.decode(toks)
-        chunk_id = generate_chunk_id(chunk, text)
+        chunk_window = f"{i}-{i + len(toks)}"
+        chunk_id = generate_chunk_id(chunk, text, chunk_window)
         chunk_metadata = metadata.copy()
         chunk_metadata["chunk_id"] = chunk_id
         chunk_metadata["document_id"] = document_id
@@ -177,7 +178,7 @@ def make_overlapped_chunks(
             source=metadata.get("source", None),
             created_timestamp=metadata.get("created_timestamp", int(time.time())),
             updated_timestamp=int(time.time()),
-            chunk_window=f"{i}-{i + len(toks)}",
+            chunk_window=chunk_window,
             chunk_tokenizer=default_tokenizer,
             chunk_embedding_model=None,  # This will be set in `VectorDBWithIndex.insert_chunks`
             content_token_count=len(toks),

llama_stack/providers/utils/vector_io/chunk_utils.py

@@ -8,7 +8,7 @@ import hashlib
 import uuid
 
 
-def generate_chunk_id(document_id: str, chunk_text: str) -> str:
+def generate_chunk_id(document_id: str, chunk_text: str, chunk_window: str | None = None) -> str:
     """
     Generate a unique chunk ID using a hash of the document ID and chunk text.
 
@@ -16,4 +16,6 @@ def generate_chunk_id(document_id: str, chunk_text: str) -> str:
     Adding usedforsecurity=False for compatibility with FIPS environments.
     """
     hash_input = f"{document_id}:{chunk_text}".encode()
+    if chunk_window:
+        hash_input += f":{chunk_window}".encode()
     return str(uuid.UUID(hashlib.md5(hash_input, usedforsecurity=False).hexdigest()))

tests/unit/providers/vector_io/test_chunk_utils.py

@@ -32,6 +32,14 @@ def test_generate_chunk_id():
     ]
 
 
+def test_generate_chunk_id_with_window():
+    chunk = Chunk(content="test", metadata={"document_id": "doc-1"})
+    chunk_id1 = generate_chunk_id("doc-1", chunk, chunk_window="0-1")
+    chunk_id2 = generate_chunk_id("doc-1", chunk, chunk_window="1-2")
+    assert chunk_id1 == "149018fe-d0eb-0f8d-5f7f-726bdd2aeedb"
+    assert chunk_id2 == "4562c1ee-9971-1f3b-51a6-7d05e5211154"
+
+
 def test_chunk_id():
     # Test with existing chunk ID
     chunk_with_id = Chunk(content="test", metadata={"document_id": "existing-id"})