Turn default caching and "use slave" option on for Views 3 in Drupal 7.

MODULENAME.module

/**
 * Implements hook_views_default_views_alter().
 */
function MODULENAME_views_default_views_alter(&$views) {
  foreach ($views as $view_name => &$view) {
    // If the view is disabled, simply continue onto the next.
    if (TRUE == $view->disabled) {
      continue;
    }

    // For each of the displays available for this `$view`, turn on slave option and cache.
    foreach ($view->display as $display_name => &$display) {
      // Each view should have the ability to use the Slave database
      // if it is available. Enabling this option as this will provide this ability.
      $views[$view_name]->display[$display_name]->display_options['query']['options']['slave'] = TRUE;

      // Turn on default caching as type `time` with results and output
      // cached for a total of one hour (3600 seconds).
      if ('none' == $display->display_options['cache']['type']) {
        $views[$view_name]->display[$display_name]->display_options['cache']['type'] = 'time';
        $views[$view_name]->display[$display_name]->display_options['cache']['results_lifespan'] = '3600';
        $views[$view_name]->display[$display_name]->display_options['cache']['results_lifespan_custom'] = '0';
        $views[$view_name]->display[$display_name]->display_options['cache']['output_lifespan'] = '3600';
        $views[$view_name]->display[$display_name]->display_options['cache']['output_lifespan_custom'] = '0';
      }
    }
  }
}