set_transient( string $transient, mixed $value, int $expiration ): bool

User Contributed Notes

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   crstauf 5 years ago

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   Unless you’re using an external object cache, when using set_transient() to update an existing transient that has an existing expiration, not providing an expiration value will maintain the existing expiration.

   For example:

   $initial = time();
   set_transient( 'foo', 'bar', 300 );
   sleep( 10 );
   $update = time();
   set_transient( 'foo', 'barbar' );

   In this case, the expiration would remain as $initial + 300 (and not change to $update + 300, or never expires), because the second set_transient() call does not include an $expiration value (only the transient’s value is updated).

   Be careful though, because you may unintentionally set a transient to never expire, if the transient expired before the second call (without the $expiration parameter) is made.
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   Nico 9 years ago

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   This example shows how to set a transient with the latest five blog posts. It expires after one day.
   It uses time constants to set the expiration time.

   // Set the arguments for the custom query
   $args = array(
       'post_type'      => 'post',
       'posts_per_page' => 5,
       'orderby'        => 'date',
       'order'          => 'DESC'
   );
   $latest_post = new WP_Query( $args );
   
   // Save the results in a transient named latest_5_posts
   set_transient( 'latest_5_posts', $latest_post, DAY_IN_SECONDS );

   To know more about how to get posts and custom post type items read the documentation of WP_Query.

   • This might seem like a good idea but caching a WP_Query in a transient like this will cause a performance hit. This is because WP_Query bulk fetches the post objects, their terms, and their taxonomies in advance into WP_Cache to avoid database queries. But when the transient is used and WP_Query is recreated, none of that has happened. As a result WordPress has to pause constantly to make small database queries to fetch the post meta and terms that were previously cached. Instead store the result as an array of post IDs. Post IDs are super fast to fetch and may even be in WP_Cache already. After all the most expensive part of the query is figuring out which post IDs match the desired results.

     Tom J Nowell 3 years ago
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   Codex 9 years ago

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   Saving the $special_query_results object for 12 hours

   set_transient( 'special_query_results', $special_query_results, 12 * HOUR_IN_SECONDS );
4. Skip to note 9 content

   Lovekesh Kumar 3 years ago

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   WordPress saves the transients expiration time in the form of a UNIX timestamp. When you look for the

   _transient_timeout_{$transient}

   option name in the options table of WordPress, it will look like 1636453079 which is in UNIX timestamp not in seconds.
   See the code on GitHub
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   Vishnu Gopal 4 years ago

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   Note that WP_CACHE has to be true in wp-config.php for transients to work:

   define('WP_CACHE', true);

   • Correction: WP_CACHE is not required to be true for transients to work.

     Vijay Hardaha 3 years ago