Pgvector - embedding retrieval

integrations/pgvector/src/haystack_integrations/document_stores/pgvector/document_store.py

@@ -52,8 +52,10 @@
 meta = EXCLUDED.meta
 """
 
+VALID_VECTOR_FUNCTIONS = ["cosine_similarity", "inner_product", "l2_distance"]
+
 VECTOR_FUNCTION_TO_POSTGRESQL_OPS = {
-    "cosine_distance": "vector_cosine_ops",
+    "cosine_similarity": "vector_cosine_ops",
     "inner_product": "vector_ip_ops",
     "l2_distance": "vector_l2_ops",
 }
@@ -70,7 +72,7 @@ def __init__(
         connection_string: str,
         table_name: str = "haystack_documents",
         embedding_dimension: int = 768,
-        vector_function: Literal["cosine_distance", "inner_product", "l2_distance"] = "cosine_distance",
+        vector_function: Literal["cosine_similarity", "inner_product", "l2_distance"] = "cosine_similarity",
         recreate_table: bool = False,
         search_strategy: Literal["exact_nearest_neighbor", "hnsw"] = "exact_nearest_neighbor",
         hnsw_recreate_index_if_exists: bool = False,
@@ -87,12 +89,23 @@ def __init__(
         :param table_name: The name of the table to use to store Haystack documents. Defaults to "haystack_documents".
         :param embedding_dimension: The dimension of the embedding. Defaults to 768.
         :param vector_function: The similarity function to use when searching for similar embeddings.
-            Defaults to "cosine_distance". Set it to one of the following values:
-        :type vector_function: Literal["cosine_distance", "inner_product", "l2_distance"]
+            Defaults to "cosine_similarity". "cosine_similarity" and "inner_product" are similarity functions and
+            higher scores indicate greater similarity between the documents.
+            "l2_distance" returns the straight-line distance between vectors,
+            and the most similar documents are the ones with the smallest score.
+
+            Important: when using the "hnsw" search strategy, an index will be created that depends on the
+            `vector_function` passed here. Make sure subsequent queries will keep using the same
+            vector similarity function in order to take advantage of the index.
+        :type vector_function: Literal["cosine_similarity", "inner_product", "l2_distance"]
         :param recreate_table: Whether to recreate the table if it already exists. Defaults to False.
         :param search_strategy: The search strategy to use when searching for similar embeddings.
             Defaults to "exact_nearest_neighbor". "hnsw" is an approximate nearest neighbor search strategy,
             which trades off some accuracy for speed; it is recommended for large numbers of documents.
+
+            Important: when using the "hnsw" search strategy, an index will be created that depends on the
+            `vector_function` passed here. Make sure subsequent queries will keep using the same
+            vector similarity function in order to take advantage of the index.
         :type search_strategy: Literal["exact_nearest_neighbor", "hnsw"]
         :param hnsw_recreate_index_if_exists: Whether to recreate the HNSW index if it already exists.
             Defaults to False. Only used if search_strategy is set to "hnsw".
@@ -107,6 +120,9 @@ def __init__(
         self.connection_string = connection_string
         self.table_name = table_name
         self.embedding_dimension = embedding_dimension
+        if vector_function not in VALID_VECTOR_FUNCTIONS:
+            msg = f"vector_function must be one of {VALID_VECTOR_FUNCTIONS}, but got {vector_function}"
+            raise ValueError(msg)
         self.vector_function = vector_function
         self.recreate_table = recreate_table
         self.search_strategy = search_strategy
@@ -423,3 +439,81 @@ def delete_documents(self, document_ids: List[str]) -> None:
         )
 
         self._execute_sql(delete_sql, error_msg="Could not delete documents from PgvectorDocumentStore")
+
+    def _embedding_retrieval(
+        self,
+        query_embedding: List[float],
+        *,
+        filters: Optional[Dict[str, Any]] = None,
+        top_k: int = 10,
+        vector_function: Optional[Literal["cosine_similarity", "inner_product", "l2_distance"]] = None,
+    ) -> List[Document]:
+        """
+        Retrieves documents that are most similar to the query embedding using a vector similarity metric.
+
+        This method is not meant to be part of the public interface of
+        `PgvectorDocumentStore` and it should not be called directly.
+        `PgvectorEmbeddingRetriever` uses this method directly and is the public interface for it.
+        :raises ValueError
+        :return: List of Documents that are most similar to `query_embedding`
+        """
+
+        if not query_embedding:
+            msg = "query_embedding must be a non-empty list of floats"
+            raise ValueError(msg)
+        if len(query_embedding) != self.embedding_dimension:
+            msg = (
+                f"query_embedding dimension ({len(query_embedding)}) does not match PgvectorDocumentStore "
+                f"embedding dimension ({self.embedding_dimension})."
+            )
+            raise ValueError(msg)
+
+        vector_function = vector_function or self.vector_function
+        if vector_function not in VALID_VECTOR_FUNCTIONS:
+            msg = f"vector_function must be one of {VALID_VECTOR_FUNCTIONS}, but got {vector_function}"
+            raise ValueError(msg)
+
+        # the vector must be a string with this format: "'[3,1,2]'"
+        query_embedding_for_postgres = f"'[{','.join(str(el) for el in query_embedding)}]'"
+
+        # to compute the scores, we use the approach described in pgvector README:
+        # https://github.com/pgvector/pgvector?tab=readme-ov-file#distances
+        # cosine_similarity and inner_product are modified from the result of the operator
+        if vector_function == "cosine_similarity":
+            score_definition = f"1 - (embedding <=> {query_embedding_for_postgres}) AS score"
+        elif vector_function == "inner_product":
+            score_definition = f"(embedding <#> {query_embedding_for_postgres}) * -1 AS score"
+        elif vector_function == "l2_distance":
+            score_definition = f"embedding <-> {query_embedding_for_postgres} AS score"
+
+        sql_select = SQL("SELECT *, {score} FROM {table_name}").format(
+            table_name=Identifier(self.table_name),
+            score=SQL(score_definition),
+        )
+
+        sql_where_clause = SQL("")
+        params = ()
+        if filters:
+            sql_where_clause, params = _convert_filters_to_where_clause_and_params(filters)
+
+        # we always want to return the most similar documents first
+        # so when using l2_distance, the sort order must be ASC
+        sort_order = "ASC" if vector_function == "l2_distance" else "DESC"
+
+        sql_sort = SQL(" ORDER BY score {sort_order} LIMIT {top_k}").format(
+            top_k=SQLLiteral(top_k),
+            sort_order=SQL(sort_order),
+        )
+
+        sql_query = sql_select + sql_where_clause + sql_sort
+
+        result = self._execute_sql(
+            sql_query,
+            params,
+            error_msg="Could not retrieve documents from PgvectorDocumentStore.",
+            cursor=self._dict_cursor,
+        )
+
+        records = result.fetchall()
+        docs = self._from_pg_to_haystack_documents(records)
+        return docs

integrations/pgvector/tests/conftest.py

@@ -7,7 +7,7 @@ def document_store(request):
     connection_string = "postgresql://postgres:postgres@localhost:5432/postgres"
     table_name = f"haystack_{request.node.name}"
     embedding_dimension = 768
-    vector_function = "cosine_distance"
+    vector_function = "cosine_similarity"
     recreate_table = True
     search_strategy = "exact_nearest_neighbor"
 

integrations/pgvector/tests/test_embedding_retrieval.py

@@ -0,0 +1,130 @@
+# SPDX-FileCopyrightText: 2023-present deepset GmbH <[email protected]>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from typing import List
+
+import pytest
+from haystack.dataclasses.document import Document
+from haystack_integrations.document_stores.pgvector import PgvectorDocumentStore
+from numpy.random import rand
+
+
+class TestEmbeddingRetrieval:
+    @pytest.fixture
+    def document_store_w_hnsw_index(self, request):
+        connection_string = "postgresql://postgres:postgres@localhost:5432/postgres"
+        table_name = f"haystack_hnsw_{request.node.name}"
+        embedding_dimension = 768
+        vector_function = "cosine_similarity"
+        recreate_table = True
+        search_strategy = "hnsw"
+
+        store = PgvectorDocumentStore(
+            connection_string=connection_string,
+            table_name=table_name,
+            embedding_dimension=embedding_dimension,
+            vector_function=vector_function,
+            recreate_table=recreate_table,
+            search_strategy=search_strategy,
+        )
+        yield store
+
+        store.delete_table()
+
+    @pytest.mark.parametrize("document_store", ["document_store", "document_store_w_hnsw_index"], indirect=True)
+    def test_embedding_retrieval_cosine_similarity(self, document_store: PgvectorDocumentStore):
+        query_embedding = [0.1] * 768
+        most_similar_embedding = [0.8] * 768
+        second_best_embedding = [0.8] * 700 + [0.1] * 3 + [0.2] * 65
+        another_embedding = rand(768).tolist()
+
+        docs = [
+            Document(content="Most similar document (cosine sim)", embedding=most_similar_embedding),
+            Document(content="2nd best document (cosine sim)", embedding=second_best_embedding),
+            Document(content="Not very similar document (cosine sim)", embedding=another_embedding),
+        ]
+
+        document_store.write_documents(docs)
+
+        results = document_store._embedding_retrieval(
+            query_embedding=query_embedding, top_k=2, filters={}, vector_function="cosine_similarity"
+        )
+        assert len(results) == 2
+        assert results[0].content == "Most similar document (cosine sim)"
+        assert results[1].content == "2nd best document (cosine sim)"
+        assert results[0].score > results[1].score
+
+    @pytest.mark.parametrize("document_store", ["document_store", "document_store_w_hnsw_index"], indirect=True)
+    def test_embedding_retrieval_inner_product(self, document_store: PgvectorDocumentStore):
+        query_embedding = [0.1] * 768
+        most_similar_embedding = [0.8] * 768
+        second_best_embedding = [0.8] * 700 + [0.1] * 3 + [0.2] * 65
+        another_embedding = rand(768).tolist()
+
+        docs = [
+            Document(content="Most similar document (inner product)", embedding=most_similar_embedding),
+            Document(content="2nd best document (inner product)", embedding=second_best_embedding),
+            Document(content="Not very similar document (inner product)", embedding=another_embedding),
+        ]
+
+        document_store.write_documents(docs)
+
+        results = document_store._embedding_retrieval(
+            query_embedding=query_embedding, top_k=2, filters={}, vector_function="inner_product"
+        )
+        assert len(results) == 2
+        assert results[0].content == "Most similar document (inner product)"
+        assert results[1].content == "2nd best document (inner product)"
+        assert results[0].score > results[1].score
+
+    @pytest.mark.parametrize("document_store", ["document_store", "document_store_w_hnsw_index"], indirect=True)
+    def test_embedding_retrieval_l2_distance(self, document_store: PgvectorDocumentStore):
+        query_embedding = [0.1] * 768
+        most_similar_embedding = [0.1] * 765 + [0.15] * 3
+        second_best_embedding = [0.1] * 700 + [0.1] * 3 + [0.2] * 65
+        another_embedding = rand(768).tolist()
+
+        docs = [
+            Document(content="Most similar document (l2 dist)", embedding=most_similar_embedding),
+            Document(content="2nd best document (l2 dist)", embedding=second_best_embedding),
+            Document(content="Not very similar document (l2 dist)", embedding=another_embedding),
+        ]
+
+        document_store.write_documents(docs)
+
+        results = document_store._embedding_retrieval(
+            query_embedding=query_embedding, top_k=2, filters={}, vector_function="l2_distance"
+        )
+        assert len(results) == 2
+        assert results[0].content == "Most similar document (l2 dist)"
+        assert results[1].content == "2nd best document (l2 dist)"
+        assert results[0].score < results[1].score
+
+    @pytest.mark.parametrize("document_store", ["document_store", "document_store_w_hnsw_index"], indirect=True)
+    def test_embedding_retrieval_with_filters(self, document_store: PgvectorDocumentStore):
+        docs = [Document(content=f"Document {i}", embedding=rand(768).tolist()) for i in range(10)]
+
+        for i in range(10):
+            docs[i].meta["meta_field"] = "custom_value" if i % 2 == 0 else "other_value"
+
+        document_store.write_documents(docs)
+
+        query_embedding = [0.1] * 768
+        filters = {"field": "meta.meta_field", "operator": "==", "value": "custom_value"}
+
+        results = document_store._embedding_retrieval(query_embedding=query_embedding, top_k=3, filters=filters)
+        assert len(results) == 3
+        for result in results:
+            assert result.meta["meta_field"] == "custom_value"
+        assert results[0].score > results[1].score > results[2].score
+
+    def test_empty_query_embedding(self, document_store: PgvectorDocumentStore):
+        query_embedding: List[float] = []
+        with pytest.raises(ValueError):
+            document_store._embedding_retrieval(query_embedding=query_embedding)
+
+    def test_query_embedding_wrong_dimension(self, document_store: PgvectorDocumentStore):
+        query_embedding = [0.1] * 4
+        with pytest.raises(ValueError):
+            document_store._embedding_retrieval(query_embedding=query_embedding)