How does LangChain handle batch processing?

LangChain handles batch processing by allowing developers to process multiple inputs simultaneously through components designed to accept lists of inputs instead of single values. This approach minimizes overhead, such as repeated API calls or sequential computations, and improves efficiency. For instance, LangChain’s LLM classes (e.g., OpenAI or ChatOpenAI) include a generate method that takes a list of prompts, sends them as a single batch request to the underlying model API, and returns all results at once. Similarly, chains—sequences of LangChain components—can process batches if their individual steps support batched operations. Developers can structure workflows to handle batches end-to-end, ensuring consistent throughput.

A key example is using the generate method with a language model. If a developer passes a list of 100 prompts to OpenAI.generate(), LangChain sends these in a single API call (if the provider supports batch requests), reducing latency and cost compared to 100 separate calls. Another example is the Chain.apply method, which processes a list of input dictionaries. For instance, a retrieval-augmented QA chain might take a batch of questions, retrieve relevant documents for each, and generate answers in parallel. Some components, like embeddings or vector stores, also support batch operations. For example, embedding 1,000 text snippets at once using OpenAIEmbeddings is more efficient than embedding them one by one, as it leverages the model’s inherent ability to process multiple inputs in parallel.

Developers should consider two main factors when implementing batch processing in LangChain. First, not all components natively support batched operations. For instance, a custom Python function in a TransformChain might need manual modification to handle lists of inputs. Second, model APIs vary in batch support: OpenAI’s API allows batches, but others might limit request sizes or charge per token, requiring developers to split large batches. Memory constraints also matter—processing 10,000 inputs at once could overload system resources. To mitigate issues, developers should test batch sizes, monitor API rate limits, and ensure error handling (e.g., retries for failed sub-batches). By aligning component configurations with model capabilities, batch processing in LangChain becomes a scalable way to handle high-volume tasks efficiently.