pgvector ivfflat query-time parameters

You can also set a parameter to control the accuracy vs. query speed tradeoff at query time. The parameter is called ivfflat.probes. This parameter specifies the number of clusters searched during a query. It is recommended to set this parameter to sqrt(lists) where lists is the parameter used above during index creation. Higher values improve query accuracy while making the query slower.

You can set the value by running:

Before executing the query, note the SET command applies to the entire session (database connection) from the point of execution. You can use a transaction-local variant using LOCAL: