How fetch_feed() works?

Question

I would like to know that how fetch_feed() works extactly?

From the Codex:

fetch_feed() caches results for 12 hours by default.

That means if I use fetch_feed( 'howtogeek.com' ), it reads the RSS feeds from howtogeek at first, it will save the result for 12 hours.

Otherwise what is the meaning of caches results for 12 hours by default.?

Answer 1

1 fetch_feed will get the feed and store it, along with the time it was fetched.

2 Every time the page with the feed is generated the time will be checked. If it is more than twelve hours ago, the feed will be reloaded. Note that this may interfere with caching plugins, who will bypass the normal page generation. Also, if the site is visited very little, the first visitor after twelve hours may still see the old feed, because WP is not particularly good at cron jobs.

3 If you don't specify another time twelve hours is the caching time for the feed. You may set up any other interval with this snipppet:

function feed_interval( $seconds ) {
  return 3600; // caching time in seconds
  }
add_filter( 'wp_feed_cache_transient_lifetime' , 'feed_interval' );