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Elasticsearch

Elasticsearch is a distributed, RESTful search and analytics engine, capable of performing both vector and lexical search. It is built on top of the Apache Lucene library.

This notebook shows how to use functionality related to the Elasticsearch vector store.

Setup​

In order to use the Elasticsearch vector search you must install the langchain-elasticsearch package.

%pip install -qU langchain-elasticsearch

Credentials​

There are two main ways to setup an Elasticsearch instance for use with:

  1. Elastic Cloud: Elastic Cloud is a managed Elasticsearch service. Signup for a free trial.

To connect to an Elasticsearch instance that does not require login credentials (starting the docker instance with security enabled), pass the Elasticsearch URL and index name along with the embedding object to the constructor.

  1. Local Install Elasticsearch: Get started with Elasticsearch by running it locally. The easiest way is to use the official Elasticsearch Docker image. See the Elasticsearch Docker documentation for more information.

Running Elasticsearch via Docker​

Example: Run a single-node Elasticsearch instance with security disabled. This is not recommended for production use.

%docker run -p 9200:9200 -e "discovery.type=single-node" -e "xpack.security.enabled=false" -e "xpack.security.http.ssl.enabled=false" docker.elastic.co/elasticsearch/elasticsearch:8.12.1

Running with Authentication​

For production, we recommend you run with security enabled. To connect with login credentials, you can use the parameters es_api_key or es_user and es_password.

pip install -qU langchain-openai
import getpass
import os

if not os.environ.get("OPENAI_API_KEY"):
  os.environ["OPENAI_API_KEY"] = getpass.getpass("Enter API key for OpenAI: ")

from langchain_openai import OpenAIEmbeddings

embeddings = OpenAIEmbeddings(model="text-embedding-3-large")
from langchain_elasticsearch import ElasticsearchStore

elastic_vector_search = ElasticsearchStore(
    es_url="http://localhost:9200",
    index_name="langchain_index",
    embedding=embeddings,
    es_user="elastic",
    es_password="changeme",
)
API Reference:ElasticsearchStore

How to obtain a password for the default "elastic" user?​

To obtain your Elastic Cloud password for the default "elastic" user:

  1. Log in to the Elastic Cloud console at https://cloud.elastic.co
  2. Go to "Security" > "Users"
  3. Locate the "elastic" user and click "Edit"
  4. Click "Reset password"
  5. Follow the prompts to reset the password

How to obtain an API key?​

To obtain an API key:

  1. Log in to the Elastic Cloud console at https://cloud.elastic.co
  2. Open Kibana and go to Stack Management > API Keys
  3. Click "Create API key"
  4. Enter a name for the API key and click "Create"
  5. Copy the API key and paste it into the api_key parameter

Elastic Cloud​

To connect to an Elasticsearch instance on Elastic Cloud, you can use either the es_cloud_id parameter or es_url.

elastic_vector_search = ElasticsearchStore(
    es_cloud_id="<cloud_id>",
    index_name="test_index",
    embedding=embeddings,
    es_user="elastic",
    es_password="changeme",
)

If you want to get best in-class automated tracing of your model calls you can also set your LangSmith API key by uncommenting below:

# os.environ["LANGSMITH_API_KEY"] = getpass.getpass("Enter your LangSmith API key: ")
# os.environ["LANGSMITH_TRACING"] = "true"

Initialization​

Elasticsearch is running locally on localhost:9200 with docker. For more details on how to connect to Elasticsearch from Elastic Cloud, see connecting with authentication above.

from langchain_elasticsearch import ElasticsearchStore

vector_store = ElasticsearchStore(
    "langchain-demo", embedding=embeddings, es_url="http://localhost:9201"
)
API Reference:ElasticsearchStore

Manage vector store​

Add items to vector store​

from uuid import uuid4

from langchain_core.documents import Document

document_1 = Document(
    page_content="I had chocalate chip pancakes and scrambled eggs for breakfast this morning.",
    metadata={"source": "tweet"},
)

document_2 = Document(
    page_content="The weather forecast for tomorrow is cloudy and overcast, with a high of 62 degrees.",
    metadata={"source": "news"},
)

document_3 = Document(
    page_content="Building an exciting new project with LangChain - come check it out!",
    metadata={"source": "tweet"},
)

document_4 = Document(
    page_content="Robbers broke into the city bank and stole $1 million in cash.",
    metadata={"source": "news"},
)

document_5 = Document(
    page_content="Wow! That was an amazing movie. I can't wait to see it again.",
    metadata={"source": "tweet"},
)

document_6 = Document(
    page_content="Is the new iPhone worth the price? Read this review to find out.",
    metadata={"source": "website"},
)

document_7 = Document(
    page_content="The top 10 soccer players in the world right now.",
    metadata={"source": "website"},
)

document_8 = Document(
    page_content="LangGraph is the best framework for building stateful, agentic applications!",
    metadata={"source": "tweet"},
)

document_9 = Document(
    page_content="The stock market is down 500 points today due to fears of a recession.",
    metadata={"source": "news"},
)

document_10 = Document(
    page_content="I have a bad feeling I am going to get deleted :(",
    metadata={"source": "tweet"},
)

documents = [
    document_1,
    document_2,
    document_3,
    document_4,
    document_5,
    document_6,
    document_7,
    document_8,
    document_9,
    document_10,
]
uuids = [str(uuid4()) for _ in range(len(documents))]

vector_store.add_documents(documents=documents, ids=uuids)
API Reference:Document
['21cca03c-9089-42d2-b41c-3d156be2b519',
 'a6ceb967-b552-4802-bb06-c0e95fce386e',
 '3a35fac4-e5f0-493b-bee0-9143b41aedae',
 '176da099-66b1-4d6a-811b-dfdfe0808d30',
 'ecfa1a30-3c97-408b-80c0-5c43d68bf5ff',
 'c0f08baa-e70b-4f83-b387-c6e0a0f36f73',
 '489b2c9c-1925-43e1-bcf0-0fa94cf1cbc4',
 '408c6503-9ba4-49fd-b1cc-95584cd914c5',
 '5248c899-16d5-4377-a9e9-736ca443ad4f',
 'ca182769-c4fc-4e25-8f0a-8dd0a525955c']

Delete items from vector store​

vector_store.delete(ids=[uuids[-1]])
True

Query vector store​

Once your vector store has been created and the relevant documents have been added you will most likely wish to query it during the running of your chain or agent. These examples also show how to use filtering when searching.

Query directly​

Performing a simple similarity search with filtering on metadata can be done as follows:

results = vector_store.similarity_search(
    query="LangChain provides abstractions to make working with LLMs easy",
    k=2,
    filter=[{"term": {"metadata.source.keyword": "tweet"}}],
)
for res in results:
    print(f"* {res.page_content} [{res.metadata}]")
* Building an exciting new project with LangChain - come check it out! [{'source': 'tweet'}]
* LangGraph is the best framework for building stateful, agentic applications! [{'source': 'tweet'}]

Similarity search with score​

If you want to execute a similarity search and receive the corresponding scores you can run:

results = vector_store.similarity_search_with_score(
    query="Will it be hot tomorrow",
    k=1,
    filter=[{"term": {"metadata.source.keyword": "news"}}],
)
for doc, score in results:
    print(f"* [SIM={score:3f}] {doc.page_content} [{doc.metadata}]")
* [SIM=0.765887] The weather forecast for tomorrow is cloudy and overcast, with a high of 62 degrees. [{'source': 'news'}]

Query by turning into retriever​

You can also transform the vector store into a retriever for easier usage in your chains.

retriever = vector_store.as_retriever(
    search_type="similarity_score_threshold", search_kwargs={"score_threshold": 0.2}
)
retriever.invoke("Stealing from the bank is a crime")
[Document(metadata={'source': 'news'}, page_content='Robbers broke into the city bank and stole $1 million in cash.'),
 Document(metadata={'source': 'news'}, page_content='The stock market is down 500 points today due to fears of a recession.'),
 Document(metadata={'source': 'website'}, page_content='Is the new iPhone worth the price? Read this review to find out.'),
 Document(metadata={'source': 'tweet'}, page_content='Building an exciting new project with LangChain - come check it out!')]

Distance Similarity Algorithm​

Elasticsearch supports the following vector distance similarity algorithms:

  • cosine
  • euclidean
  • dot_product

The cosine similarity algorithm is the default.

You can specify the similarity Algorithm needed via the similarity parameter.

NOTE: Depending on the retrieval strategy, the similarity algorithm cannot be changed at query time. It is needed to be set when creating the index mapping for field. If you need to change the similarity algorithm, you need to delete the index and recreate it with the correct distance_strategy.

db = ElasticsearchStore.from_documents(
    docs,
    embeddings,
    es_url="http://localhost:9200",
    index_name="test",
    distance_strategy="COSINE",
    # distance_strategy="EUCLIDEAN_DISTANCE"
    # distance_strategy="DOT_PRODUCT"
)

Retrieval Strategies​

Elasticsearch has big advantages over other vector only databases from its ability to support a wide range of retrieval strategies. In this notebook we will configure ElasticsearchStore to support some of the most common retrieval strategies.

By default, ElasticsearchStore uses the DenseVectorStrategy (was called ApproxRetrievalStrategy prior to version 0.2.0).

DenseVectorStrategy​

This will return the top k most similar vectors to the query vector. The k parameter is set when the ElasticsearchStore is initialized. The default value is 10.

from langchain_elasticsearch import DenseVectorStrategy

db = ElasticsearchStore.from_documents(
    docs,
    embeddings,
    es_url="http://localhost:9200",
    index_name="test",
    strategy=DenseVectorStrategy(),
)

docs = db.similarity_search(
    query="What did the president say about Ketanji Brown Jackson?", k=10
)
API Reference:DenseVectorStrategy

This example will show how to configure ElasticsearchStore to perform a hybrid retrieval, using a combination of approximate semantic search and keyword based search.

We use RRF to balance the two scores from different retrieval methods.

To enable hybrid retrieval, we need to set hybrid=True in the DenseVectorStrategy constructor.

db = ElasticsearchStore.from_documents(
    docs,
    embeddings,
    es_url="http://localhost:9200",
    index_name="test",
    strategy=DenseVectorStrategy(hybrid=True),
)

When hybrid is enabled, the query performed will be a combination of approximate semantic search and keyword based search.

It will use rrf (Reciprocal Rank Fusion) to balance the two scores from different retrieval methods.

Note: RRF requires Elasticsearch 8.9.0 or above.

{
    "retriever": {
        "rrf": {
            "retrievers": [
                {
                    "standard": {
                        "query": {
                            "bool": {
                                "filter": [],
                                "must": [{"match": {"text": {"query": "foo"}}}],
                            }
                        },
                    },
                },
                {
                    "knn": {
                        "field": "vector",
                        "filter": [],
                        "k": 1,
                        "num_candidates": 50,
                        "query_vector": [1.0, ..., 0.0],
                    },
                },
            ]
        }
    }
}

Example: Dense vector search with Embedding Model in Elasticsearch​

This example will show how to configure ElasticsearchStore to use the embedding model deployed in Elasticsearch for dense vector retrieval.

To use this, specify the model_id in DenseVectorStrategy constructor via the query_model_id argument.

NOTE: This requires the model to be deployed and running in Elasticsearch ML node. See notebook example on how to deploy the model with eland.

DENSE_SELF_DEPLOYED_INDEX_NAME = "test-dense-self-deployed"

# Note: This does not have an embedding function specified
# Instead, we will use the embedding model deployed in Elasticsearch
db = ElasticsearchStore(
    es_cloud_id="<your cloud id>",
    es_user="elastic",
    es_password="<your password>",
    index_name=DENSE_SELF_DEPLOYED_INDEX_NAME,
    query_field="text_field",
    vector_query_field="vector_query_field.predicted_value",
    strategy=DenseVectorStrategy(model_id="sentence-transformers__all-minilm-l6-v2"),
)

# Setup a Ingest Pipeline to perform the embedding
# of the text field
db.client.ingest.put_pipeline(
    id="test_pipeline",
    processors=[
        {
            "inference": {
                "model_id": "sentence-transformers__all-minilm-l6-v2",
                "field_map": {"query_field": "text_field"},
                "target_field": "vector_query_field",
            }
        }
    ],
)

# creating a new index with the pipeline,
# not relying on langchain to create the index
db.client.indices.create(
    index=DENSE_SELF_DEPLOYED_INDEX_NAME,
    mappings={
        "properties": {
            "text_field": {"type": "text"},
            "vector_query_field": {
                "properties": {
                    "predicted_value": {
                        "type": "dense_vector",
                        "dims": 384,
                        "index": True,
                        "similarity": "l2_norm",
                    }
                }
            },
        }
    },
    settings={"index": {"default_pipeline": "test_pipeline"}},
)

db.from_texts(
    ["hello world"],
    es_cloud_id="<cloud id>",
    es_user="elastic",
    es_password="<cloud password>",
    index_name=DENSE_SELF_DEPLOYED_INDEX_NAME,
    query_field="text_field",
    vector_query_field="vector_query_field.predicted_value",
    strategy=DenseVectorStrategy(model_id="sentence-transformers__all-minilm-l6-v2"),
)

# Perform search
db.similarity_search("hello world", k=10)

SparseVectorStrategy (ELSER)​

This strategy uses Elasticsearch's sparse vector retrieval to retrieve the top-k results. We only support our own "ELSER" embedding model for now.

NOTE: This requires the ELSER model to be deployed and running in Elasticsearch ml node.

To use this, specify SparseVectorStrategy (was called SparseVectorRetrievalStrategy prior to version 0.2.0) in the ElasticsearchStore constructor. You will need to provide a model ID.

from langchain_elasticsearch import SparseVectorStrategy

# Note that this example doesn't have an embedding function. This is because we infer the tokens at index time and at query time within Elasticsearch.
# This requires the ELSER model to be loaded and running in Elasticsearch.
db = ElasticsearchStore.from_documents(
    docs,
    es_cloud_id="<cloud id>",
    es_user="elastic",
    es_password="<cloud password>",
    index_name="test-elser",
    strategy=SparseVectorStrategy(model_id=".elser_model_2"),
)

db.client.indices.refresh(index="test-elser")

results = db.similarity_search(
    "What did the president say about Ketanji Brown Jackson", k=4
)
print(results[0])
API Reference:SparseVectorStrategy

DenseVectorScriptScoreStrategy​

This strategy uses Elasticsearch's script score query to perform exact vector retrieval (also known as brute force) to retrieve the top-k results. (This strategy was called ExactRetrievalStrategy prior to version 0.2.0.)

To use this, specify DenseVectorScriptScoreStrategy in ElasticsearchStore constructor.

from langchain_elasticsearch import SparseVectorStrategy

db = ElasticsearchStore.from_documents(
    docs,
    embeddings,
    es_url="http://localhost:9200",
    index_name="test",
    strategy=DenseVectorScriptScoreStrategy(),
)
API Reference:SparseVectorStrategy

BM25Strategy​

Finally, you can use full-text keyword search.

To use this, specify BM25Strategy in ElasticsearchStore constructor.

from langchain_elasticsearch import BM25Strategy

db = ElasticsearchStore.from_documents(
    docs,
    es_url="http://localhost:9200",
    index_name="test",
    strategy=BM25Strategy(),
)
API Reference:BM25Strategy

BM25RetrievalStrategy​

This strategy allows the user to perform searches using pure BM25 without vector search.

To use this, specify BM25RetrievalStrategy in ElasticsearchStore constructor.

Note that in the example below, the embedding option is not specified, indicating that the search is conducted without using embeddings.

from langchain_elasticsearch import ElasticsearchStore

db = ElasticsearchStore(
    es_url="http://localhost:9200",
    index_name="test_index",
    strategy=ElasticsearchStore.BM25RetrievalStrategy(),
)

db.add_texts(
    ["foo", "foo bar", "foo bar baz", "bar", "bar baz", "baz"],
)

results = db.similarity_search(query="foo", k=10)
print(results)
API Reference:ElasticsearchStore

Customise the Query​

With custom_query parameter at search, you are able to adjust the query that is used to retrieve documents from Elasticsearch. This is useful if you want to use a more complex query, to support linear boosting of fields.

# Example of a custom query thats just doing a BM25 search on the text field.
def custom_query(query_body: dict, query: str):
    """Custom query to be used in Elasticsearch.
    Args:
        query_body (dict): Elasticsearch query body.
        query (str): Query string.
    Returns:
        dict: Elasticsearch query body.
    """
    print("Query Retriever created by the retrieval strategy:")
    print(query_body)
    print()

    new_query_body = {"query": {"match": {"text": query}}}

    print("Query thats actually used in Elasticsearch:")
    print(new_query_body)
    print()

    return new_query_body


results = db.similarity_search(
    "What did the president say about Ketanji Brown Jackson",
    k=4,
    custom_query=custom_query,
)
print("Results:")
print(results[0])

Customize the Document Builder​

With doc_builder parameter at search, you are able to adjust how a Document is being built using data retrieved from Elasticsearch. This is especially useful if you have indices which were not created using Langchain.

from typing import Dict

from langchain_core.documents import Document


def custom_document_builder(hit: Dict) -> Document:
    src = hit.get("_source", {})
    return Document(
        page_content=src.get("content", "Missing content!"),
        metadata={
            "page_number": src.get("page_number", -1),
            "original_filename": src.get("original_filename", "Missing filename!"),
        },
    )


results = db.similarity_search(
    "What did the president say about Ketanji Brown Jackson",
    k=4,
    doc_builder=custom_document_builder,
)
print("Results:")
print(results[0])
API Reference:Document

Usage for retrieval-augmented generation​

For guides on how to use this vector store for retrieval-augmented generation (RAG), see the following sections:

FAQ

Question: Im getting timeout errors when indexing documents into Elasticsearch. How do I fix this?​

One possible issue is your documents might take longer to index into Elasticsearch. ElasticsearchStore uses the Elasticsearch bulk API which has a few defaults that you can adjust to reduce the chance of timeout errors.

This is also a good idea when you're using SparseVectorRetrievalStrategy.

The defaults are:

  • chunk_size: 500
  • max_chunk_bytes: 100MB

To adjust these, you can pass in the chunk_size and max_chunk_bytes parameters to the ElasticsearchStore add_texts method.

    vector_store.add_texts(
        texts,
        bulk_kwargs={
            "chunk_size": 50,
            "max_chunk_bytes": 200000000
        }
    )

Upgrading to ElasticsearchStore

If you're already using Elasticsearch in your langchain based project, you may be using the old implementations: ElasticVectorSearch and ElasticKNNSearch which are now deprecated. We've introduced a new implementation called ElasticsearchStore which is more flexible and easier to use. This notebook will guide you through the process of upgrading to the new implementation.

What's new?​

The new implementation is now one class called ElasticsearchStore which can be used for approximate dense vector, exact dense vector, sparse vector (ELSER), BM25 retrieval and hybrid retrieval, via strategies.

I am using ElasticKNNSearch​

Old implementation:


from langchain_community.vectorstores.elastic_vector_search import ElasticKNNSearch

db = ElasticKNNSearch(
  elasticsearch_url="http://localhost:9200",
  index_name="test_index",
  embedding=embedding
)

New implementation:


from langchain_elasticsearch import ElasticsearchStore, DenseVectorStrategy

db = ElasticsearchStore(
  es_url="http://localhost:9200",
  index_name="test_index",
  embedding=embedding,
  # if you use the model_id
  # strategy=DenseVectorStrategy(model_id="test_model")
  # if you use hybrid search
  # strategy=DenseVectorStrategy(hybrid=True)
)

I am using ElasticVectorSearch​

Old implementation:


from langchain_community.vectorstores.elastic_vector_search import ElasticVectorSearch

db = ElasticVectorSearch(
  elasticsearch_url="http://localhost:9200",
  index_name="test_index",
  embedding=embedding
)

API Reference:ElasticVectorSearch

New implementation:


from langchain_elasticsearch import ElasticsearchStore, DenseVectorScriptScoreStrategy

db = ElasticsearchStore(
  es_url="http://localhost:9200",
  index_name="test_index",
  embedding=embedding,
  strategy=DenseVectorScriptScoreStrategy()
)

db.client.indices.delete(
    index="test-metadata, test-elser, test-basic",
    ignore_unavailable=True,
    allow_no_indices=True,
)

API reference​

For detailed documentation of all ElasticSearchStore features and configurations head to the API reference: https://python.langchain.com/api_reference/elasticsearch/vectorstores/langchain_elasticsearch.vectorstores.ElasticsearchStore.html

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