src/main/java/com/conveyal/gtfs/GTFS.java
public static void delete (String feedId, DataSource dataSource) throws SQLException, InvalidNamespaceException {
        LOG.info("Deleting all tables (dropping schema) for {} feed namespace.", feedId);
        Connection connection = null;
        try {
            connection = dataSource.getConnection();
            ensureValidNamespace(feedId);
            // Mark entry in feeds table as deleted.
            String deleteFeedEntrySql = "update feeds set deleted = true where namespace = ?";
            PreparedStatement deleteFeedStatement = connection.prepareStatement(deleteFeedEntrySql);
            deleteFeedStatement.setString(1, feedId);
            deleteFeedStatement.executeUpdate();
            // Drop all tables bearing the feedId namespace.
            // Note: It does not appear to be possible to use prepared statements with "drop schema."
            String dropSchemaSql = String.format("DROP SCHEMA %s CASCADE", feedId);
            Statement statement = connection.createStatement();
            statement.executeUpdate(dropSchemaSql);
            // Commit the changes.
            connection.commit();
        } catch (InvalidNamespaceException | SQLException e) {
            LOG.error(String.format("Could not drop feed for namespace %s", feedId), e);
            throw e;
        } finally {
            if (connection != null) DbUtils.closeQuietly(connection);
        }
    }
public static void delete (String feedId, DataSource dataSource) throws SQLException, InvalidNamespaceException {
        LOG.info("Deleting all tables (dropping schema) for {} feed namespace.", feedId);
        Connection connection = null;
        try {
            connection = dataSource.getConnection();
            ensureValidNamespace(feedId);
            // Mark entry in feeds table as deleted.
            String deleteFeedEntrySql = "update feeds set deleted = true where namespace = ?";
            PreparedStatement deleteFeedStatement = connection.prepareStatement(deleteFeedEntrySql);
            deleteFeedStatement.setString(1, feedId);
            deleteFeedStatement.executeUpdate();
            // Drop all tables bearing the feedId namespace.
            // Note: It does not appear to be possible to use prepared statements with "drop schema."
            String dropSchemaSql = String.format("DROP SCHEMA %s CASCADE", feedId);
            Statement statement = connection.createStatement();
            statement.executeUpdate(dropSchemaSql);
            // Commit the changes.
            connection.commit();
        } catch (InvalidNamespaceException | SQLException e) {
            LOG.error(String.format("Could not drop feed for namespace %s", feedId), e);
            throw e;
        } finally {
            if (connection != null) DbUtils.closeQuietly(connection);
        }
    }
Deletes all tables for the specified feed. Simply put, this is a "drop schema" SQL statement called on the feed's
namespace.