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PODesign pattern for memcached data caching
 

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    <p>It's easy to wrap optional memcached caching around your existing database queries. For example:</p> <p>Old (DB-only):</p> <pre><code>function getX x = get from db return x end </code></pre> <p>New (DB with memcache):</p> <pre><code>function getX x = get from memcache if found return x endif x = get from db set x in memcache return x end </code></pre> <p>The thing is though, that's not always how you want to cache. For instance take the following two queries:</p> <pre><code>-- get all items (recordset) SELECT * FROM items; -- get one item (record) SELECT * FROM items WHERE pkid = 42; </code></pre> <p>If I was to use the above pseudo-code to handle the caching, I would be storing all fields of item 42 twice. Once in the big record set and once on its own. Whereas I'd rather do something like this:</p> <pre><code>SELECT pkid FROM items; </code></pre> <p>and cache that index of PK's. Then cache each record individually as well.</p> <p>So in summary, the data access strategy that will work best for the DB doesn't neatly fit the memcache strategy. Since I want the memcache layer to be optional (i.e. if memcache is down, the site still works) I kind of want to have the best of both worlds, but to do so, I'm pretty sure I'll need to maintain a lot of the queries in 2 different forms (1. fetch index, then records; and 2. fetch recordset in one query). It gets more complicated with pagination. With the DB you'd do LIMIT/OFFSET SQL queries, but with memcache you'd just fetch the index of PK's and then batch-get the relevant slice of the array.</p> <p>I'm not sure how to neatly design this, does anyone have any suggestions?</p> <p>Better yet, if you've come up against this yourself. How do you handle it?</p>
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