haystack/docs-website/versioned_docs/version-2.21/document-stores/pgvectordocumentstore.mdx

---
title: "PgvectorDocumentStore"
id: pgvectordocumentstore
slug: "/pgvectordocumentstore"
---

# PgvectorDocumentStore

<div className="key-value-table">

|  |  |
| --- | --- |
| API reference | [Pgvector](/reference/integrations-pgvector)                                                       |
| GitHub link   | https://github.com/deepset-ai/haystack-core-integrations/tree/main/integrations/pgvector/ |

</div>

Pgvector is an extension for PostgreSQL that enhances its capabilities with vector similarity search. It builds upon the classic features of PostgreSQL, such as ACID compliance and point-in-time recovery, and introduces the ability to perform exact and approximate nearest neighbor search using vectors.

For more information, see the [pgvector repository](https://github.com/pgvector/pgvector).

Pgvector Document Store supports embedding retrieval and metadata filtering.

## Installation

To quickly set up a PostgreSQL database with pgvector, you can use Docker:

```shell
docker run -d -p 5432:5432 -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres -e POSTGRES_DB=postgres ankane/pgvector
```

For more information on installing pgvector, visit the [pgvector GitHub repository](https://github.com/pgvector/pgvector).

To use pgvector with Haystack, install the `pgvector-haystack` integration:

```shell
pip install pgvector-haystack
```

## Usage

### Connection String

Define the connection string to your PostgreSQL database in the `PG_CONN_STR` environment variable. Two formats are supported:

**URI format:**

```shell
export PG_CONN_STR="postgresql://USER:PASSWORD@HOST:PORT/DB_NAME"
```

**Keyword/value format:**

```shell
export PG_CONN_STR="host=HOST port=PORT dbname=DB_NAME user=USER password=PASSWORD"
```

:::caution Special Characters in Connection URIs

When using the URI format, special characters in the password must be [percent-encoded](https://en.wikipedia.org/wiki/Percent-encoding). Otherwise, connection errors may occur. A password like `p=ssword` would cause the error `psycopg.OperationalError: [Errno -2] Name or service not known`.

For example, if your password is `p=ssword`, the connection string should be:

```shell
export PG_CONN_STR="postgresql://postgres:p%3Dssword@localhost:5432/postgres"
```

Alternatively, use the keyword/value format, which does not require percent-encoding:

```shell
export PG_CONN_STR="host=localhost port=5432 dbname=postgres user=postgres password=p=ssword"
```

:::

For more details, see the [PostgreSQL connection string documentation](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING).

## Initialization

Initialize a `PgvectorDocumentStore` object that’s connected to the PostgreSQL database and writes documents to it:

```python
from haystack_integrations.document_stores.pgvector import PgvectorDocumentStore
from haystack import Document

document_store = PgvectorDocumentStore(
    embedding_dimension=768,
    vector_function="cosine_similarity",
    recreate_table=True,
    search_strategy="hnsw",
)

document_store.write_documents([
    Document(content="This is first", embedding=[0.1]*768),
    Document(content="This is second", embedding=[0.3]*768)
    ])
print(document_store.count_documents())
```

To learn more about the initialization parameters, see our [API docs](/reference/integrations-pgvector#pgvectordocumentstore).

To properly compute embeddings for your documents, you can use a Document Embedder (for instance, the [`SentenceTransformersDocumentEmbedder`](../pipeline-components/embedders/sentencetransformersdocumentembedder.mdx)).

### Supported Retrievers

- [`PgvectorEmbeddingRetriever`](../pipeline-components/retrievers/pgvectorembeddingretriever.mdx): An embedding-based Retriever that fetches documents from the Document Store based on a query embedding provided to the Retriever.
- [`PgvectorKeywordRetriever`](../pipeline-components/retrievers/pgvectorembeddingretriever.mdx): A keyword-based Retriever that fetches documents matching a query from the Pgvector Document Store.