For parameter $transient, if memcached is not enabled the name should be 172 characters or less in length as WordPress will prefix your name with “_transient_” or “_transient_timeout_” in the options table (depending on whether it expires or not). Longer key names will silently fail. See Trac #15058.
If a transient exists, this function will update the transient’s expiration time.
NB: transients that never expire are autoloaded, whereas transients with an expiration time are not autoloaded. Consider this when adding transients that may not be needed on every page, and thus do not need to be autoloaded, impacting page performance.
WordPress provides some constants for specifying time in seconds. Instead of multiplying out integers, see Transients_API#Using_Time_Constants.
Transient key names are limited to 191 characters due to the database schema in the wp_options table ( option_name: varchar(191) ).
In WordPress versions previous to 4.4, the length limitation was 45 in set_transient (now 172) and 64 in the database (now 191).
Source
File: wp-includes/option.php
function set_transient( $transient, $value, $expiration = 0 ) {
$expiration = (int) $expiration;
/**
* Filters a specific transient before its value is set.
*
* The dynamic portion of the hook name, `$transient`, refers to the transient name.
*
* @since 3.0.0
* @since 4.2.0 The `$expiration` parameter was added.
* @since 4.4.0 The `$transient` parameter was added.
*
* @param mixed $value New value of transient.
* @param int $expiration Time until expiration in seconds.
* @param string $transient Transient name.
*/
$value = apply_filters( "pre_set_transient_{$transient}", $value, $expiration, $transient );
/**
* Filters the expiration for a transient before its value is set.
*
* The dynamic portion of the hook name, `$transient`, refers to the transient name.
*
* @since 4.4.0
*
* @param int $expiration Time until expiration in seconds. Use 0 for no expiration.
* @param mixed $value New value of transient.
* @param string $transient Transient name.
*/
$expiration = apply_filters( "expiration_of_transient_{$transient}", $expiration, $value, $transient );
if ( wp_using_ext_object_cache() ) {
$result = wp_cache_set( $transient, $value, 'transient', $expiration );
} else {
$transient_timeout = '_transient_timeout_' . $transient;
$transient_option = '_transient_' . $transient;
if ( false === get_option( $transient_option ) ) {
$autoload = 'yes';
if ( $expiration ) {
$autoload = 'no';
add_option( $transient_timeout, time() + $expiration, '', 'no' );
}
$result = add_option( $transient_option, $value, '', $autoload );
} else {
// If expiration is requested, but the transient has no timeout option,
// delete, then re-create transient rather than update.
$update = true;
if ( $expiration ) {
if ( false === get_option( $transient_timeout ) ) {
delete_option( $transient_option );
add_option( $transient_timeout, time() + $expiration, '', 'no' );
$result = add_option( $transient_option, $value, '', 'no' );
$update = false;
} else {
update_option( $transient_timeout, time() + $expiration );
}
}
if ( $update ) {
$result = update_option( $transient_option, $value );
}
}
}
if ( $result ) {
/**
* Fires after the value for a specific transient has been set.
*
* The dynamic portion of the hook name, `$transient`, refers to the transient name.
*
* @since 3.0.0
* @since 3.6.0 The `$value` and `$expiration` parameters were added.
* @since 4.4.0 The `$transient` parameter was added.
*
* @param mixed $value Transient value.
* @param int $expiration Time until expiration in seconds.
* @param string $transient The name of the transient.
*/
do_action( "set_transient_{$transient}", $value, $expiration, $transient );
/**
* Fires after the value for a transient has been set.
*
* @since 3.0.0
* @since 3.6.0 The `$value` and `$expiration` parameters were added.
*
* @param string $transient The name of the transient.
* @param mixed $value Transient value.
* @param int $expiration Time until expiration in seconds.
*/
do_action( 'setted_transient', $transient, $value, $expiration );
}
return $result;
}