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POEfficient Query Generation for Permutations of Tags
 

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  1. POEfficient Query Generation for Permutations of Tags
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    <p>Here's a simplified version of a problem I'm encountering at work. The details have been changed and more generalized so I can explain it easier.</p> <p>Let's say you have a blog engine that allows blog posts to be assigned tags when they're created. So I could write a post titled "My Vacation in Italy", and I decide to add the following tags to it: <code>has-photos</code>, <code>vacation</code>, <code>family</code>. As part of my blog engine, I can create custom actions based on groups of tags. So I decided before writing it that any post with the tags <code>has-photos</code> and <code>family</code> will be automatically shared on Facebook. When that post is created for the first time, I have to then automatically cross-reference all of its tags with all actions that can be performed on combinations of those tags.</p> <p>When the "My Vacation in Italy" post is saved, I then need to look-up all actions for the following groups of tags:</p> <ul> <li><code>has-photos</code></li> <li><code>vacation</code></li> <li><code>family</code></li> <li><code>has-photos</code> &amp; <code>vacation</code></li> <li><code>has-photos</code> &amp; <code>family</code></li> <li><code>vacation</code> &amp; <code>family</code></li> <li><code>has-photos</code> &amp; <code>vacation</code> &amp; <code>family</code></li> </ul> <p>Generating that query is trivial, I just get all the permutations of any length from the original tag set of the post. It comes out to being <code>2^N - 1</code> possibilities of tag combinations.</p> <p>The problem I'm running into arises when you put this up against large datasets. What we're dealing with are the following:</p> <ul> <li>10,000+ "posts" arriving daily</li> <li>20+ "tags" per "post"</li> <li>1,000s of "actions" existing already when blog posts arrive, with varying #s of tags they're triggered on</li> </ul> <p>When a post arrives with 20 tags, that comes out to a little over a million permutations I'd be generating a query for. Even if my database allowed me to send query strings to it that large (hint: it doesn't), it'd still take forever to run.</p> <p>Is there a clever solution to this I'm not thinking of? Right now as I see it, I'm left with one possibility:</p> <h3>Actions use OR instead of AND</h3> <p>I could change it so that when you create a pre-defined action, the tags it acts on are implicitly OR'ed instead of AND'ed. Then the tag combinations drops from <code>2^N - 1</code> to just <code>N</code>. Unfortunately this would severely limit the usefulness of the "tag action" feature.</p> <p>Edit: I'm not necessarily looking for an answer in SQL. Just a different approach to solving this problem, even if it's just a high level description.</p>
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    1. COCan't you do this when you create the post, when presumably you have the tags to start off with and so don't need to hit the database? Fire off a (presumably async) action to do whatever is needed. (If this doesn't solve your actual problem, then you may have oversimplified; or I may have misunderstood :-)
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    2. CO@JamesAylett Yes, forcing the user to explicitly declare actions every time they create a post would "solve" this. Sadly that's not an option with my real scenario. What I call "blog posts" in the question are actually generated from other software, and that software has no concept of what actions may or may not be created or present.
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    3. CONo, don't get them to declare the actions. You said that the tags select which actions happen, so presumably the tags are generated by the software as it stands.
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