Improve usability of WipeOutCloudSqlAction (#1118)

* Improve usability of WipeOutCloudSqlAction

Replace the "drop owned" statement with ones that drops only tables and
sequences. The former statement also drops default grants for the
nomulus user, which must be restored before the database can be used by
the nomulus server and tools.

core/src/main/java/google/registry/batch/WipeOutCloudSqlAction.java

@@ -19,6 +19,7 @@ import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
 import static javax.servlet.http.HttpServletResponse.SC_OK;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.flogger.FluentLogger;
 import google.registry.config.RegistryConfig.Config;
@@ -28,10 +29,11 @@ import google.registry.request.Response;
 import google.registry.request.auth.Auth;
 import google.registry.util.Retrier;
 import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.function.Supplier;
 import javax.inject.Inject;
-import org.flywaydb.core.api.FlywayException;
 
 /**
  * Wipes out all Cloud SQL data in a Nomulus GCP environment.
@@ -80,13 +82,13 @@ public class WipeOutCloudSqlAction implements Runnable {
     try {
       retrier.callWithRetry(
           () -> {
-            try (Connection conn = connectionSupplier.get();
-                Statement statement = conn.createStatement()) {
-              statement.execute("drop owned by schema_deployer;");
+            try (Connection conn = connectionSupplier.get()) {
+              dropAllTables(conn, listTables(conn));
+              dropAllSequences(conn, listSequences(conn));
             }
             return null;
           },
-          e -> !(e instanceof FlywayException));
+          e -> !(e instanceof SQLException));
       response.setStatus(SC_OK);
       response.setPayload("Wiped out Cloud SQL in " + projectId);
     } catch (RuntimeException e) {
@@ -95,4 +97,69 @@ public class WipeOutCloudSqlAction implements Runnable {
       response.setPayload("Failed to wipe out Cloud SQL in " + projectId);
     }
   }
+
+  /** Returns a list of all tables in the public schema of a Postgresql database. */
+  static ImmutableList<String> listTables(Connection connection) throws SQLException {
+    try (ResultSet resultSet =
+        connection.getMetaData().getTables(null, null, null, new String[] {"TABLE"})) {
+      ImmutableList.Builder<String> tables = new ImmutableList.Builder<>();
+      while (resultSet.next()) {
+        String schema = resultSet.getString("TABLE_SCHEM");
+        if (schema == null || !schema.equalsIgnoreCase("public")) {
+          continue;
+        }
+        String tableName = resultSet.getString("TABLE_NAME");
+        tables.add("public.\"" + tableName + "\"");
+      }
+      return tables.build();
+    }
+  }
+
+  static void dropAllTables(Connection conn, ImmutableList<String> tables) throws SQLException {
+    if (tables.isEmpty()) {
+      return;
+    }
+
+    try (Statement statement = conn.createStatement()) {
+      for (String table : tables) {
+        statement.addBatch(String.format("DROP TABLE IF EXISTS %s CASCADE;", table));
+      }
+      for (int code : statement.executeBatch()) {
+        if (code == Statement.EXECUTE_FAILED) {
+          throw new RuntimeException("Failed to drop some tables. Please check.");
+        }
+      }
+    }
+  }
+
+  /** Returns a list of all sequences in a Postgresql database. */
+  static ImmutableList<String> listSequences(Connection conn) throws SQLException {
+    try (Statement statement = conn.createStatement();
+        ResultSet resultSet =
+            statement.executeQuery("SELECT c.relname FROM pg_class c WHERE c.relkind = 'S';")) {
+      ImmutableList.Builder<String> sequences = new ImmutableList.Builder<>();
+      while (resultSet.next()) {
+        sequences.add('\"' + resultSet.getString(1) + '\"');
+      }
+      return sequences.build();
+    }
+  }
+
+  static void dropAllSequences(Connection conn, ImmutableList<String> sequences)
+      throws SQLException {
+    if (sequences.isEmpty()) {
+      return;
+    }
+
+    try (Statement statement = conn.createStatement()) {
+      for (String sequence : sequences) {
+        statement.addBatch(String.format("DROP SEQUENCE IF EXISTS %s CASCADE;", sequence));
+      }
+      for (int code : statement.executeBatch()) {
+        if (code == Statement.EXECUTE_FAILED) {
+          throw new RuntimeException("Failed to drop some sequences. Please check.");
+        }
+      }
+    }
+  }
 }