How to ingest large data from pgVector database and perform similarity search?

Question

I have millions of records in pgVector db as id, content, metadata and embedding. How do I add all the embedded data from the database into the vector store and perform similarity search?

SearchRequest searchRequest = SearchRequest.query("Which customers are named John?")
    .withTopK(4)
    .withSimilarityThreshold(0.8);

List<Document> results =  vectorStore.doSimilaritySearch(searchRequest);