cache-menu 越来越大的表

I have debugged this in D7, not sure if the same is true for D6. I have observed the same problem on a recently launched site with a small amount of data. After a while the cache_menu table was as big as the rest of the database. The majority of the cache entries are menu items (cid starts with menu_item:). The hash value in the cid is calculated from the normalized request path given to Drupal which is available in $_GET['q']. The menu system has an interesting feature:

When responding to a page request, the menu system looks to see if the path requested by the browser is registered as a menu item with a callback. If not, the system searches up the menu tree for the most complete match with a callback it can find. If the path a/b/i is requested in the tree above, the callback for a/b would be used.

This can lead to multiple cache_menu entries for the same menu_item: By appending a slash followed by a random string to the path of an existing page when making a request a different hash is produced.

一日偶尔发生mysql数据库报错，说data packet的大小超过了允许的mysql数据库的大小，然后dump出长长一段数据，是cache_menu里的数据。

检查了cache_menu表，发现里面保存的有些cache数据大小已经达到500KB，的确是比较吃惊，简单的check一下这些数据，保存的是menu树的信息，有些是book的导航等，但是检查数据会发现，这些数据里存在大量的冗余，开发者只是简单的把数据结构cache在这里，而实际上稍微做些调整，可能可以得到更好的存储性能。