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shown how Drupal core uses cache_clear_all() to delete a single cache item
avpaderno
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To delete from the cache the cache item set with cache_set($cache_id, $temp_data, 'cache', CACHE_TEMPORARY); it's enough to call cache_clear_all($cache_id, 'cache');. Despite the name, cache_clear_all() doesn't necessarily clear all the cache; it does so only when no parameter is passed to the function.

Usually Drupal core uses cache_clear_all() to clear all the cache. In some cases, it uses that function to clear a specific cache item, which is what Drupal core does in variable_set().

function variable_set($name, $value) {
  global $conf;
  db_merge('variable')->key(array('name' => $name))
    ->fields(array('value' => serialize($value)))
    ->execute();
  cache_clear_all('variables', 'cache_bootstrap');
  $conf[$name] = $value;
}

In that code, the deleted cache item is the one whose cache ID is variables, contained in the cache_bootstrap cache bin.

avpaderno
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