Querying Vectors - ParadeDB

This is a beta feature available in versions 0.25.0 and above. See How Vector Search Works for background, and Indexing Vectors to set up the index used in these examples.

Vector search returns the rows whose embeddings are closest to a query vector. In ParadeDB, this is an ORDER BY <distance> ... LIMIT k query over a vector column in the ParadeDB index. When one of ParadeDB’s search operators is present at the same level as the ORDER BY ... LIMIT, ParadeDB can accelerate the vector search query.

Unfiltered Nearest Neighbors

When you are not filtering, use pdb.all(), which matches every row:

SELECT id, description
FROM mock_items
WHERE id @@@ pdb.all()
ORDER BY embedding <=> '[1, 2, 3, 4, 5, 6, 7, 8]'
LIMIT 5;

// Vector search support for Drizzle is coming very soon.

# Vector search support for Django is coming very soon.

# Vector search support for SQLAlchemy is coming very soon.

# Vector search support for Rails is coming very soon.

// Vector search support for EF Core is coming very soon.

The <=> operator computes cosine distance, so this returns the five rows whose embeddings are nearest the query vector [1, 2, 3, 4, 5, 6, 7, 8]. This operator must match the operator class the column was indexed with. Otherwise, ParadeDB cannot use the index to order results and falls back to a slower brute force sort.

Operator	Distance	Operator class
`<->`	L2	`vector_l2_ops`
`<=>`	Cosine	`vector_cosine_ops`
`<#>`	Inner product	`vector_ip_ops`

Filtered Nearest Neighbors

To search within a subset of rows, replace pdb.all() with a real predicate using any of the search operators. For instance, the following query finds the nearest neighbors among results whose category contains the term footwear. Note the lowercase footwear — the default tokenizer lowercases terms, so Footwear would not match.

SELECT id, description
FROM mock_items
WHERE category === 'footwear'
ORDER BY embedding <=> '[1, 2, 3, 4, 5, 6, 7, 8]'
LIMIT 5;

// Vector search support for Drizzle is coming very soon.

# Vector search support for Django is coming very soon.

# Vector search support for SQLAlchemy is coming very soon.

# Vector search support for Rails is coming very soon.

// Vector search support for EF Core is coming very soon.

Every field you filter on (e.g. category above) must also be part of the ParadeDB index. Filters on unindexed fields cannot be evaluated by the ParadeDB index, forcing Postgres to recheck them afterward and eliminating the benefit of combining vector search with filtering.

Verifying Pushdown

Use EXPLAIN to confirm ParadeDB is accelerating the vector search. Look for a Custom Scan with an Exec Method of TopKScanExecState in the query plan:

EXPLAIN SELECT id, description
FROM mock_items
WHERE category === 'footwear'
ORDER BY embedding <=> '[1, 2, 3, 4, 5, 6, 7, 8]'
LIMIT 5;

Expected Response

                               QUERY PLAN
------------------------------------------------------------------------
 Limit
   ->  Custom Scan (ParadeDB Base Scan) on mock_items
         Table: mock_items
         Index: search_idx
         Exec Method: TopKScanExecState
         Scores: false
            TopK Order By: embedding <=> vector asc
            TopK Limit: 5
         Tantivy Query: {"with_index":{"query":{"term":{"field":"category","value":"footwear"}}}}

Notice that the category === 'footwear' filter was pushed down into the same index scan that performs the vector search. Without pushdown, the filter would run as a separate step after the nearest neighbors were fetched. If you do not see a TopKScanExecState, the query fell back to a less efficient sort. This usually means the distance operator does not match the index operator class, the query is missing a LIMIT, or an ORDER BY or filter field is not indexed.

​Unfiltered Nearest Neighbors

​Filtered Nearest Neighbors

​Verifying Pushdown

Unfiltered Nearest Neighbors

Filtered Nearest Neighbors

Verifying Pushdown