perf(spanner-jdbc): cache JDBC metadata query strings

Cache the SQL strings that are loaded from disk for the standard JDBC metadata queries.

Author: olavloite

java-spanner-jdbc/src/main/java/com/google/cloud/spanner/jdbc/JdbcDatabaseMetaData.java

@@ -26,10 +26,12 @@
 import com.google.cloud.spanner.Type.StructField;
 import com.google.cloud.spanner.connection.Connection.InternalMetadataQuery;
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableSet;
 import java.io.BufferedReader;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.sql.Connection;
 import java.sql.DatabaseMetaData;
 import java.sql.ResultSet;
@@ -40,6 +42,8 @@
 import java.util.Collections;
 import java.util.Properties;
 import java.util.Scanner;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 /** {@link DatabaseMetaData} implementation for Cloud Spanner */
 class JdbcDatabaseMetaData extends AbstractJdbcWrapper implements DatabaseMetaData {
@@ -50,18 +54,19 @@ class JdbcDatabaseMetaData extends AbstractJdbcWrapper implements DatabaseMetaDa
   private static final String PRODUCT_NAME = "Google Cloud Spanner";
   private static final String POSTGRESQL_PRODUCT_NAME = PRODUCT_NAME + " PostgreSQL";
 
+  private static final ConcurrentMap<String, String> SQL_CACHE = new ConcurrentHashMap<>();
+
   @VisibleForTesting
   static String readSqlFromFile(String filename, Dialect dialect) {
-    InputStream in;
-    switch (dialect) {
-      case POSTGRESQL:
-        in = JdbcDatabaseMetaData.class.getResourceAsStream("postgresql/" + filename);
-        break;
-      case GOOGLE_STANDARD_SQL:
-      default:
-        in = JdbcDatabaseMetaData.class.getResourceAsStream(filename);
-    }
-    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
+    return SQL_CACHE.computeIfAbsent(
+        filename + "/" + dialect, (key) -> loadSqlFromFile(filename, dialect));
+  }
+
+  private static String loadSqlFromFile(String filename, Dialect dialect) {
+    String resourcePath = dialect == Dialect.POSTGRESQL ? "postgresql/" + filename : filename;
+    InputStream in = JdbcDatabaseMetaData.class.getResourceAsStream(resourcePath);
+    Preconditions.checkNotNull(in, "Resource not found: " + resourcePath);
+    BufferedReader reader = new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8));
     StringBuilder builder = new StringBuilder();
     try (Scanner scanner = new Scanner(reader)) {
       while (scanner.hasNextLine()) {

java-spanner-jdbc/src/test/java/com/google/cloud/spanner/jdbc/JdbcDatabaseMetaDataTest.java

@@ -19,6 +19,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
@@ -574,4 +575,12 @@ public void testGetUserName() throws SQLException, IOException {
     DatabaseMetaData meta = new JdbcDatabaseMetaData(connection);
     assertEquals("test@test-project.iam.gserviceaccount.com", meta.getUserName());
   }
+
+  @Test
+  public void testReadSqlFromFileCaching() {
+    String sql1 = JdbcDatabaseMetaData.readSqlFromFile("DatabaseMetaData_GetTables.sql", dialect);
+    String sql2 = JdbcDatabaseMetaData.readSqlFromFile("DatabaseMetaData_GetTables.sql", dialect);
+    assertNotNull(sql1);
+    assertSame(sql1, sql2);
+  }
 }