Checked other resources

• This is a bug, not a usage question. For questions, please use the LangChain Forum (https://forum.langchain.com/).
• I added a clear and descriptive title that summarizes this issue.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
• I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example).
• I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.

Example Code

from langchain.vectorstores import Chroma
from langchain_openai import AzureOpenAIEmbeddings
import os
import chromadb

embeddings = AzureOpenAIEmbeddings(
                azure_endpoint=os.environ['API_BASE'],
                api_key=os.environ['EMBEDDING_API_KEY'],
                model=os.environ['EMBEDDING_MODEL_NAME'],
            )

#
persist_directory = "xxxx"

collection = Chroma(
        persist_directory=persist_directory, 
        embedding_function=embeddings,
        collection_metadata={"hnsw:num_threads":1}
    )

Error Message and Stack Trace (if applicable)

pip freeze:

langchain==0.3.27
chromadb==1.0.15
langchain_openai==0.3.28

Errors info:

collection = Chroma( persist_directory=persist_directory, embedding_function=embeddings, )

ValueError: num_threads must be less than or equal to the number of available threads

Description

pip freeze:

langchain==0.3.27
chromadb==1.0.15
langchain_openai==0.3.28

Errors info:

I have created a vector db with langchain.vectorstores.Chroma as below, using local server with 8 cpus.

vectordb = Chroma.from_documents(
            chunks, embedding=embeddings, persist_directory=persist_directory)

But when I use another server( on Azure) with 4 cpus, loading the vectordb will failed with error:

collection = Chroma(
        persist_directory=persist_directory, 
        embedding_function=embeddings,
    )
>ValueError: num_threads must be less than or equal to the number of available threads

Question:

・How can I change the num_thread in langchain.vectorstores.Chroma when loading a vectordb from files? In this case, I have to set num_thread=4 , according to the error?

System Info

System Information

OS: Linux
OS Version: langchain-ai/langchain#1 SMP PREEMPT_DYNAMIC Wed Apr 30 17:38:54 UTC 2025
Python Version: 3.13.5 | packaged by Anaconda, Inc. | (main, Jun 12 2025, 16:09:02) [GCC 11.2.0]

Package Information

langchain_core: 0.3.72
langchain: 0.3.27
langchain_community: 0.3.27
langsmith: 0.4.13
langchain_openai: 0.3.28
langchain_text_splitters: 0.3.9

Optional packages not installed

langserve

Other Dependencies

aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
httpx<1,>=0.23.0: Installed. No version info available.
jsonpatch<2.0,>=1.33: Installed. No version info available.
langchain-anthropic;: Installed. No version info available.
langchain-aws;: Installed. No version info available.
langchain-azure-ai;: Installed. No version info available.
langchain-cohere;: Installed. No version info available.
langchain-community;: Installed. No version info available.
langchain-core<1.0.0,>=0.3.66: Installed. No version info available.
langchain-core<1.0.0,>=0.3.68: Installed. No version info available.
langchain-core<1.0.0,>=0.3.72: Installed. No version info available.
langchain-deepseek;: Installed. No version info available.
langchain-fireworks;: Installed. No version info available.
langchain-google-genai;: Installed. No version info available.
langchain-google-vertexai;: Installed. No version info available.
langchain-groq;: Installed. No version info available.
langchain-huggingface;: Installed. No version info available.
langchain-mistralai;: Installed. No version info available.
langchain-ollama;: Installed. No version info available.
langchain-openai;: Installed. No version info available.
langchain-perplexity;: Installed. No version info available.
langchain-text-splitters<1.0.0,>=0.3.9: Installed. No version info available.
langchain-together;: Installed. No version info available.
langchain-xai;: Installed. No version info available.
langchain<1.0.0,>=0.3.26: Installed. No version info available.
langsmith-pyo3>=0.1.0rc2;: Installed. No version info available.
langsmith>=0.1.125: Installed. No version info available.
langsmith>=0.1.17: Installed. No version info available.
langsmith>=0.3.45: Installed. No version info available.
numpy>=1.26.2;: Installed. No version info available.
numpy>=2.1.0;: Installed. No version info available.
openai-agents>=0.0.3;: Installed. No version info available.
openai<2.0.0,>=1.86.0: Installed. No version info available.
opentelemetry-api>=1.30.0;: Installed. No version info available.
opentelemetry-exporter-otlp-proto-http>=1.30.0;: Installed. No version info available.
opentelemetry-sdk>=1.30.0;: Installed. No version info available.
orjson>=3.9.14;: Installed. No version info available.
packaging>=23.2: Installed. No version info available.
pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
pydantic<3,>=1: Installed. No version info available.
pydantic<3.0.0,>=2.7.4: Installed. No version info available.
pydantic>=2.7.4: Installed. No version info available.
pytest>=7.0.0;: Installed. No version info available.
PyYAML>=5.3: Installed. No version info available.
requests-toolbelt>=1.0.0: Installed. No version info available.
requests<3,>=2: Installed. No version info available.
requests>=2.0.0: Installed. No version info available.
rich>=13.9.4;: Installed. No version info available.
SQLAlchemy<3,>=1.4: Installed. No version info available.
tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
tiktoken<1,>=0.7: Installed. No version info available.
typing-extensions>=4.7: Installed. No version info available.
vcrpy>=7.0.0;: Installed. No version info available.
zstandard>=0.23.0: Installed. No version info available.