Added bulk loading example [skip ci]

Author: ankane

README.md

@@ -37,6 +37,7 @@ Or check out an example:
 
 - [Embeddings](src/test/java/com/pgvector/OpenAITest.java) with OpenAI
 - [Binary embeddings](src/test/java/com/pgvector/CohereTest.java) with Cohere
+- [Bulk loading](src/test/java/com/pgvector/LoadingTest.java) with `COPY`
 
 ## JDBC (Java)
 

src/test/java/com/pgvector/LoadingTest.java

@@ -0,0 +1,82 @@
+package com.pgvector;
+
+import java.io.UnsupportedEncodingException;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.ArrayList;
+import com.pgvector.PGvector;
+import org.postgresql.PGConnection;
+import org.postgresql.copy.CopyIn;
+import org.postgresql.copy.CopyManager;
+import org.postgresql.core.BaseConnection;
+import org.junit.jupiter.api.Test;
+
+public class LoadingTest {
+    @Test
+    void example() throws SQLException, UnsupportedEncodingException {
+        if (System.getenv("TEST_LOADING") == null) {
+            return;
+        }
+
+        // generate random data
+        int rows = 1000000;
+        int dimensions = 128;
+        ArrayList<float[]> embeddings = new ArrayList<>(rows);
+        for (int i = 0; i < rows; i++) {
+            float[] embedding = new float[dimensions];
+            for (int j = 0; j < dimensions; j++) {
+                embedding[j] = (float) Math.random();
+            }
+            embeddings.add(embedding);
+        }
+
+        // enable extension
+        Connection conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/pgvector_example");
+        Statement setupStmt = conn.createStatement();
+        setupStmt.executeUpdate("CREATE EXTENSION IF NOT EXISTS vector");
+        PGvector.addVectorType(conn);
+
+        // create table
+        setupStmt.executeUpdate("DROP TABLE IF EXISTS items");
+        setupStmt.executeUpdate("CREATE TABLE items (id bigserial, embedding vector(128))");
+
+        // load data
+        System.out.println("Loading 1000000 rows");
+
+        CopyManager copyManager = new CopyManager((BaseConnection) conn);
+        // TODO use binary format
+        CopyIn copyIn = copyManager.copyIn("COPY items (embedding) FROM STDIN");
+        for (int i = 0; i < rows; i++) {
+            if (i % 10000 == 0) {
+                System.out.print(".");
+            }
+
+            PGvector embedding = new PGvector(embeddings.get(i));
+            byte[] bytes = (embedding.getValue() + "\n").getBytes("UTF-8");
+            copyIn.writeToCopy(bytes, 0, bytes.length);
+        }
+        copyIn.endCopy();
+
+        System.out.println("\nSuccess!");
+
+        // create any indexes *after* loading initial data (skipping for this example)
+        boolean createIndex = false;
+        if (createIndex) {
+            System.out.println("Creating index");
+            Statement createIndexStmt = conn.createStatement();
+            createIndexStmt.executeUpdate("SET maintenance_work_mem = '8GB'");
+            createIndexStmt.executeUpdate("SET max_parallel_maintenance_workers = 7");
+            createIndexStmt.executeUpdate("CREATE INDEX ON items USING hnsw (embedding vector_cosine_ops)");
+        }
+
+        // update planner statistics for good measure
+        Statement analyzeStmt = conn.createStatement();
+        analyzeStmt.executeUpdate("ANALYZE items");
+
+        conn.close();
+    }
+}