[Mediawiki-l] how to make cached never expire

I want to make the cache never expire, my mediawiki is for off line read . What's is 'apiThumbCacheExpiry' max value ? i can make thumbs never expire? $wgHTTPTimeout by default is 3 milliseconds , i had increase this value , but the response of pages are slow while the thumbs images are downloading , and sometimes when reached this time the the page go blank and no result. how to make the page show first, and them images thumb show while we are reading the page or article.?

regards

$wgHTTPTimeout = 90000; //milisegundos $wgHTTPProxy = "http://PyproxySquidIP:SquidPort";

$wgForeignFileRepos[] = array( 'class' => 'ForeignAPIRepo', 'name' => 'shared', 'hashLevels' => '2', 'hasSharedCache' => $wgCacheSharedUploads, 'apibase' => 'http://commons.wikimedia.org/w/api.php', 'fetchDescription' => false, // Optional 'descriptionCacheExpiry' => 432000, // 12*5 hours, optional 'apiThumbCacheExpiry' => 864000, // 12 hours, optional, but required for local thumb caching );