perf: use PLAN mode to get result metadata

src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcPreparedStatement.java

@@ -29,7 +29,6 @@
 import java.sql.PreparedStatement;
 import java.sql.Ref;
 import java.sql.ResultSet;
-import java.sql.ResultSetMetaData;
 import java.sql.RowId;
 import java.sql.SQLException;
 import java.sql.SQLXML;
@@ -232,14 +231,6 @@ public void setArray(int parameterIndex, Array value) throws SQLException {
     parameters.setParameter(parameterIndex, value, Types.ARRAY);
   }
 
-  @Override
-  public ResultSetMetaData getMetaData() throws SQLException {
-    checkClosed();
-    try (ResultSet rs = executeQuery()) {
-      return rs.getMetaData();
-    }
-  }
-
   @Override
   public void setDate(int parameterIndex, Date value, Calendar cal) throws SQLException {
     checkClosed();

src/main/java/com/google/cloud/spanner/jdbc/AbstractJdbcStatement.java

@@ -18,6 +18,7 @@
 
 import com.google.cloud.spanner.Options;
 import com.google.cloud.spanner.Options.QueryOption;
+import com.google.cloud.spanner.ReadContext.QueryAnalyzeMode;
 import com.google.cloud.spanner.SpannerException;
 import com.google.cloud.spanner.connection.StatementResult;
 import com.google.cloud.spanner.connection.StatementResult.ClientSideStatementType;
@@ -147,6 +148,20 @@ private void resetStatementTimeout(StatementTimeout originalTimeout) throws SQLE
     }
   }
 
+  /**
+   * Executes a SQL statement on the connection of this {@link Statement} as a query using the given
+   * {@link QueryAnalyzeMode}.
+   *
+   * @param statement the SQL statement to executed
+   * @param analyzeMode the {@link QueryAnalyzeMode} to use
+   * @return the result of the SQL statement as a {@link ResultSet}
+   * @throws SQLException if a database error occurs.
+   */
+  ResultSet analyzeQuery(com.google.cloud.spanner.Statement statement, QueryAnalyzeMode analyzeMode)
+      throws SQLException {
+    return executeQuery(statement, analyzeMode);
+  }
+
   /**
    * Executes a SQL statement on the connection of this {@link Statement} as a query.
    *
@@ -157,11 +172,24 @@ private void resetStatementTimeout(StatementTimeout originalTimeout) throws SQLE
    */
   ResultSet executeQuery(com.google.cloud.spanner.Statement statement, QueryOption... options)
       throws SQLException {
+    return executeQuery(statement, null, options);
+  }
+
+  private ResultSet executeQuery(
+      com.google.cloud.spanner.Statement statement,
+      QueryAnalyzeMode analyzeMode,
+      QueryOption... options)
+      throws SQLException {
     StatementTimeout originalTimeout = setTemporaryStatementTimeout();
     try {
-      return JdbcResultSet.of(
-          this,
-          connection.getSpannerConnection().executeQuery(statement, getQueryOptions(options)));
+      com.google.cloud.spanner.ResultSet resultSet;
+      if (analyzeMode == null) {
+        resultSet =
+            connection.getSpannerConnection().executeQuery(statement, getQueryOptions(options));
+      } else {
+        resultSet = connection.getSpannerConnection().analyzeQuery(statement, analyzeMode);
+      }
+      return JdbcResultSet.of(this, resultSet);
     } catch (SpannerException e) {
       throw JdbcSqlExceptionFactory.of(e);
     } finally {

src/main/java/com/google/cloud/spanner/jdbc/JdbcPreparedStatement.java

@@ -17,11 +17,17 @@
 package com.google.cloud.spanner.jdbc;
 
 import com.google.cloud.spanner.Options.QueryOption;
+import com.google.cloud.spanner.ReadContext.QueryAnalyzeMode;
+import com.google.cloud.spanner.ResultSets;
 import com.google.cloud.spanner.Statement;
+import com.google.cloud.spanner.Struct;
+import com.google.cloud.spanner.Type;
 import com.google.cloud.spanner.connection.StatementParser;
 import com.google.cloud.spanner.jdbc.JdbcParameterStore.ParametersInfo;
+import com.google.common.collect.ImmutableList;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
 
 /** Implementation of {@link PreparedStatement} for Cloud Spanner. */
@@ -86,4 +92,20 @@ public JdbcParameterMetaData getParameterMetaData() throws SQLException {
     checkClosed();
     return new JdbcParameterMetaData(this);
   }
+
+  @Override
+  public ResultSetMetaData getMetaData() throws SQLException {
+    checkClosed();
+    if (StatementParser.INSTANCE.isUpdateStatement(sql)) {
+      // Return metadata for an empty result set as DML statements do not return any results (as a
+      // result set).
+      com.google.cloud.spanner.ResultSet resultSet =
+          ResultSets.forRows(Type.struct(), ImmutableList.<Struct>of());
+      resultSet.next();
+      return new JdbcResultSetMetaData(JdbcResultSet.of(resultSet), this);
+    }
+    try (ResultSet rs = analyzeQuery(createStatement(), QueryAnalyzeMode.PLAN)) {
+      return rs.getMetaData();
+    }
+  }
 }

src/test/java/com/google/cloud/spanner/jdbc/JdbcPreparedStatementTest.java

@@ -25,6 +25,7 @@
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
+import com.google.cloud.spanner.ReadContext.QueryAnalyzeMode;
 import com.google.cloud.spanner.ResultSet;
 import com.google.cloud.spanner.ResultSets;
 import com.google.cloud.spanner.Statement;
@@ -293,7 +294,7 @@ public void testGetResultSetMetadata() throws SQLException {
                     .set("AMOUNT")
                     .to(Math.PI)
                     .build()));
-    when(connection.executeQuery(Statement.of(sql))).thenReturn(rs);
+    when(connection.analyzeQuery(Statement.of(sql), QueryAnalyzeMode.PLAN)).thenReturn(rs);
     try (JdbcPreparedStatement ps =
         new JdbcPreparedStatement(createMockConnection(connection), sql)) {
       ResultSetMetaData metadata = ps.getMetaData();
@@ -306,4 +307,15 @@ public void testGetResultSetMetadata() throws SQLException {
       assertEquals(Types.DOUBLE, metadata.getColumnType(3));
     }
   }
+
+  @Test
+  public void testGetResultSetMetaDataForDml() throws SQLException {
+    Connection connection = mock(Connection.class);
+    try (JdbcPreparedStatement ps =
+        new JdbcPreparedStatement(
+            createMockConnection(connection), "UPDATE FOO SET BAR=1 WHERE TRUE")) {
+      ResultSetMetaData metadata = ps.getMetaData();
+      assertEquals(0, metadata.getColumnCount());
+    }
+  }
 }

src/test/java/com/google/cloud/spanner/jdbc/it/ITJdbcPreparedStatementTest.java

@@ -16,18 +16,20 @@
 
 package com.google.cloud.spanner.jdbc.it;
 
+import static com.google.cloud.spanner.testing.EmulatorSpannerHelper.isUsingEmulator;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.junit.Assume.assumeFalse;
 
-import com.google.api.client.util.Base64;
 import com.google.cloud.spanner.IntegrationTest;
 import com.google.cloud.spanner.jdbc.ITAbstractJdbcTest;
 import com.google.common.base.Strings;
+import com.google.common.io.BaseEncoding;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.StringReader;
@@ -38,6 +40,7 @@
 import java.sql.ParameterMetaData;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.sql.Timestamp;
@@ -222,7 +225,7 @@ private static Long[] parseLongArray(String value) {
   }
 
   private static byte[] parseBytes(String value) {
-    return Base64.decodeBase64(value);
+    return BaseEncoding.base64().decode(value);
   }
 
   private List<Singer> createSingers() {
@@ -825,6 +828,53 @@ public void test08_InsertAllColumnTypes() throws SQLException {
     }
   }
 
+  @Test
+  public void test09_MetaData_FromQuery() throws SQLException {
+    assumeFalse("The emulator does not support PLAN mode", isUsingEmulator());
+    try (Connection con = createConnection()) {
+      try (PreparedStatement ps =
+          con.prepareStatement("SELECT * FROM TableWithAllColumnTypes WHERE ColInt64=?")) {
+        ResultSetMetaData metadata = ps.getMetaData();
+        assertEquals(22, metadata.getColumnCount());
+        int index = 0;
+        assertEquals("ColInt64", metadata.getColumnLabel(++index));
+        assertEquals("ColFloat64", metadata.getColumnLabel(++index));
+        assertEquals("ColBool", metadata.getColumnLabel(++index));
+        assertEquals("ColString", metadata.getColumnLabel(++index));
+        assertEquals("ColStringMax", metadata.getColumnLabel(++index));
+        assertEquals("ColBytes", metadata.getColumnLabel(++index));
+        assertEquals("ColBytesMax", metadata.getColumnLabel(++index));
+        assertEquals("ColDate", metadata.getColumnLabel(++index));
+        assertEquals("ColTimestamp", metadata.getColumnLabel(++index));
+        assertEquals("ColCommitTS", metadata.getColumnLabel(++index));
+        assertEquals("ColNumeric", metadata.getColumnLabel(++index));
+        assertEquals("ColInt64Array", metadata.getColumnLabel(++index));
+        assertEquals("ColFloat64Array", metadata.getColumnLabel(++index));
+        assertEquals("ColBoolArray", metadata.getColumnLabel(++index));
+        assertEquals("ColStringArray", metadata.getColumnLabel(++index));
+        assertEquals("ColStringMaxArray", metadata.getColumnLabel(++index));
+        assertEquals("ColBytesArray", metadata.getColumnLabel(++index));
+        assertEquals("ColBytesMaxArray", metadata.getColumnLabel(++index));
+        assertEquals("ColDateArray", metadata.getColumnLabel(++index));
+        assertEquals("ColTimestampArray", metadata.getColumnLabel(++index));
+        assertEquals("ColNumericArray", metadata.getColumnLabel(++index));
+        assertEquals("ColComputed", metadata.getColumnLabel(++index));
+      }
+    }
+  }
+
+  @Test
+  public void test10_MetaData_FromDML() throws SQLException {
+    try (Connection con = createConnection()) {
+      try (PreparedStatement ps =
+          con.prepareStatement(
+              "UPDATE TableWithAllColumnTypes SET ColBool=FALSE WHERE ColInt64=?")) {
+        ResultSetMetaData metadata = ps.getMetaData();
+        assertEquals(0, metadata.getColumnCount());
+      }
+    }
+  }
+
   private void assertDefaultParameterMetaData(ParameterMetaData pmd, int expectedParamCount)
       throws SQLException {
     assertEquals(expectedParamCount, pmd.getParameterCount());