CrateDB is a distributed and scalable SQL database for storing and analyzing massive amounts of data in near real-time, even with complex queries. It is PostgreSQL-compatible, based on Lucene, and inheriting from Elasticsearch.

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Installation and Setup

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Setup CrateDB

There are two ways to get started with CrateDB quickly. Alternatively, choose other CrateDB installation options.

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Start CrateDB on your local machine

Example: Run a single-node CrateDB instance with security disabled, using Docker or Podman. This is not recommended for production use. 
docker run --name=cratedb --rm \
  --publish=4200:4200 --publish=5432:5432 --env=CRATE_HEAP_SIZE=2g \
  crate:latest -Cdiscovery.type=single-node

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Deploy cluster on CrateDB Cloud

CrateDB Cloud is a managed CrateDB service. Sign up for a free trial.

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Install Client

Install the most recent version of the langchain-cratedb package and a few others that are needed for this tutorial. 
pip install --upgrade langchain-cratedb langchain-openai unstructured

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Documentation

For a more detailed walkthrough of the CrateDB wrapper, see using LangChain with CrateDB. See also all features of CrateDB to learn about other functionality provided by CrateDB.

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Features

The CrateDB adapter for LangChain provides APIs to use CrateDB as vector store, document loader, and storage for chat messages.

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Vector Store

Use the CrateDB vector store functionality around FLOAT_VECTOR and KNN_MATCH for similarity search and other purposes. See also CrateDBVectorStore Tutorial. Make sure you’ve configured a valid OpenAI API key. 
export OPENAI_API_KEY=sk-XJZ...

from langchain_community.document_loaders import UnstructuredURLLoader
from langchain_cratedb import CrateDBVectorStore
from langchain_openai import OpenAIEmbeddings
from langchain.text_splitter import CharacterTextSplitter

loader = UnstructuredURLLoader(urls=["https://github.com/langchain-ai/langchain/raw/refs/tags/langchain-core==0.3.28/docs/docs/how_to/state_of_the_union.txt"])
documents = loader.load()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
docs = text_splitter.split_documents(documents)

embeddings = OpenAIEmbeddings()

# Connect to a self-managed CrateDB instance on localhost.
CONNECTION_STRING = "crate://?schema=testdrive"

store = CrateDBVectorStore.from_documents(
    documents=docs,
    embedding=embeddings,
    collection_name="state_of_the_union",
    connection=CONNECTION_STRING,
)

query = "What did the president say about Ketanji Brown Jackson"
docs_with_score = store.similarity_search_with_score(query)

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Document Loader

Load load documents from a CrateDB database table, using the document loader CrateDBLoader, which is based on SQLAlchemy. See also CrateDBLoader Tutorial. To use the document loader in your applications: 
import sqlalchemy as sa
from langchain_community.utilities import SQLDatabase
from langchain_cratedb import CrateDBLoader

# Connect to a self-managed CrateDB instance on localhost.
CONNECTION_STRING = "crate://?schema=testdrive"

db = SQLDatabase(engine=sa.create_engine(CONNECTION_STRING))

loader = CrateDBLoader(
    'SELECT * FROM sys.summits LIMIT 42',
    db=db,
)
documents = loader.load()

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Chat Message History

Use CrateDB as the storage for your chat messages. See also CrateDBChatMessageHistory Tutorial. To use the chat message history in your applications: 
from langchain_cratedb import CrateDBChatMessageHistory

# Connect to a self-managed CrateDB instance on localhost.
CONNECTION_STRING = "crate://?schema=testdrive"

message_history = CrateDBChatMessageHistory(
    session_id="test-session",
    connection=CONNECTION_STRING,
)

message_history.add_user_message("hi!")

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Full Cache

The standard / full cache avoids invoking the LLM when the supplied prompt is exactly the same as one encountered already. See also CrateDBCache Example. To use the full cache in your applications: 
import sqlalchemy as sa
from langchain.globals import set_llm_cache
from langchain_openai import ChatOpenAI, OpenAIEmbeddings
from langchain_cratedb import CrateDBCache

# Configure cache.
engine = sa.create_engine("crate://crate@localhost:4200/?schema=testdrive")
set_llm_cache(CrateDBCache(engine))

# Invoke LLM conversation.
llm = ChatOpenAI(
    model_name="chatgpt-4o-latest",
    temperature=0.7,
)
print()
print("Asking with full cache:")
answer = llm.invoke("What is the answer to everything?")
print(answer.content)

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Semantic Cache

The semantic cache allows users to retrieve cached prompts based on semantic similarity between the user input and previously cached inputs. It also avoids invoking the LLM when not needed. See also CrateDBSemanticCache Example. To use the semantic cache in your applications: 
import sqlalchemy as sa
from langchain.globals import set_llm_cache
from langchain_openai import ChatOpenAI, OpenAIEmbeddings
from langchain_cratedb import CrateDBSemanticCache

# Configure embeddings.
embeddings = OpenAIEmbeddings(model="text-embedding-3-small")

# Configure cache.
engine = sa.create_engine("crate://crate@localhost:4200/?schema=testdrive")
set_llm_cache(
    CrateDBSemanticCache(
        embedding=embeddings,
        connection=engine,
        search_threshold=1.0,
    )
)

# Invoke LLM conversation.
llm = ChatOpenAI(model_name="chatgpt-4o-latest")
print()
print("Asking with semantic cache:")
answer = llm.invoke("What is the answer to everything?")
print(answer.content)