function is_blog_installed() {
  global $wpdb;

  /*
	 * Check cache first. If options table goes away and we have true
	 * cached, oh well.
	 */
  if ( wp_cache_get( 'is_blog_installed' ) ) {
    return true;
  }

  $suppress = $wpdb->suppress_errors();

  if ( ! wp_installing() ) {
    $alloptions = wp_load_alloptions();
  }

  // If siteurl is not set to autoload, check it specifically.
  if ( ! isset( $alloptions['siteurl'] ) ) {
    $installed = $wpdb->get_var( "SELECT option_value FROM $wpdb->options WHERE option_name = 'siteurl'" );
  } else {
    $installed = $alloptions['siteurl'];
  }

  $wpdb->suppress_errors( $suppress );

  $installed = ! empty( $installed );
  wp_cache_set( 'is_blog_installed', $installed );

  if ( $installed ) {
    return true;
  }

  // If visiting repair.php, return true and let it take over.
  if ( defined( 'WP_REPAIRING' ) ) {
    return true;
  }

  $suppress = $wpdb->suppress_errors();

  /*
	 * Loop over the WP tables. If none exist, then scratch installation is allowed.
	 * If one or more exist, suggest table repair since we got here because the
	 * options table could not be accessed.
	 */
  $wp_tables = $wpdb->tables();
  foreach ( $wp_tables as $table ) {
    // The existence of custom user tables shouldn't suggest an unwise state or prevent a clean installation.
    if ( defined( 'CUSTOM_USER_TABLE' ) && CUSTOM_USER_TABLE === $table ) {
      continue;
    }

    if ( defined( 'CUSTOM_USER_META_TABLE' ) && CUSTOM_USER_META_TABLE === $table ) {
      continue;
    }

    $described_table = $wpdb->get_results( "DESCRIBE $table;" );
    if (
      ( ! $described_table && empty( $wpdb->last_error ) ) ||
      ( is_array( $described_table ) && 0 === count( $described_table ) )
    ) {
      continue;
    }

    // One or more tables exist. This is not good.

    wp_load_translations_early();

    // Die with a DB error.
    $wpdb->error = sprintf(
      /* translators: %s: Database repair URL. */
      __( 'One or more database tables are unavailable. The database may need to be <a href="%s">repaired</a>.' ),
      'maint/repair.php?referrer=is_blog_installed'
    );

    dead_db();
  }

  $wpdb->suppress_errors( $suppress );

  wp_cache_set( 'is_blog_installed', false );

  return false;
}