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POWhere is the best place to put cache-evicting logic in an AppEngine application?
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  1. POWhere is the best place to put cache-evicting logic in an AppEngine application?
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    copied!<p>I've written an application for Google AppEngine, and I'd like to make use of the memcache API to cut down on per-request CPU time. I've profiled the application and found that a large chunk of the CPU time is in template rendering and API calls to the datastore, and after chatting with a co-worker I jumped (perhaps a bit early?) to the conclusion that caching a chunk of a page's rendered HTML would cut down on the CPU time per request significantly. The caching pattern is pretty clean, but the question of <em>where</em> to put this logic of caching and evicting is a bit of a mystery to me.</p> <p>For example, imagine an application's main page has an Announcements section. This section would need to be re-rendered after:</p> <ul> <li>first read for anyone in the account,</li> <li>a new announcement being added, and</li> <li>an old announcement being deleted</li> </ul> <p>Some options of where to put the <code>evict_announcements_section_from_cache()</code> method call:</p> <ul> <li>in the Announcement Model's <code>.delete()</code>, and <code>.put()</code> methods</li> <li>in the RequestHandler's <code>.post()</code> method</li> <li>anywhere else?</li> </ul> <p>Then in the RequestHandler's get page, I could potentially call <code>get_announcements_section()</code> which would follow the standard memcache pattern (check cache, add to cache on miss, return value) and pass that HTML down to the template for that chunk of the page.</p> <p>Is it the typical design pattern to put the cache-evicting logic in the Model, or the Controller/RequestHandler, or somewhere else? Ideally I'd like to avoid having evicting logic with tentacles all over the code.</p>
 

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