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POCaching data from MySQL DB - technique and appropriate STL container?
 

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    <p>I am designing a data caching system that could have a very large amount of records held at a time, and I need to know what stl container to use and how to use it. The application is that I have an extremely large DB of records for users - when they log in to my system I want to pull their record and cache some data such as username and several important properties. As they interact with the system, I update and access their properties. Several properties are very volatile and I'm doing this to avoid "banging" on the DB with many transactions. Also, I rarely need to be using the database for sorting or anything - I'm using this just like a glorified binary save file (which is why I am happy to cache records to memory..); a more important goal for me is to be able to scale to huge numbers of users.</p> <p>When the user logs out, server shuts down, or <strong>periodically in round-robin fashion (just in case..)</strong>, I want to write their data back to the DB.</p> <p>The server keeps its own:</p> <pre><code>vector &lt;UserData *&gt; loggedInUsers; </code></pre> <p>With UserData keeping things like username (string) and other properties from the DB, as well as other temporary data like network handles. </p> <p>My first Q is, if I need to find a specific user in this vector, what's the <strong>fastest</strong> way to do that and is there a different stl container I can use to do this faster? What I do now is create an iterator, start it at loggedInUsers.begin() and iterate to .end(), checking *iter->username == "foo" and returning when it's found. If the username is at the end of the vector, or if the vector has 5000 users, this is a significant delay.</p> <p>My second Q is, how can I round-robin schedule this data to be written back to the DB? I can call a function every time I'm ready to write a few records to the DB. But I can't hold an iterator to the vector, because it will become invalid. What I'd like to do is have a rotating queue where I can access the head of the queue, persist it to the DB, then rotate it to be the end of the queue. That seems like a lot of overhead.. what type could I use to do this better?</p> <p>My third Q is, I'm using MySQL server and libmysqlclient connector/C.. is there any kind of built in caching that could solve this problem "for free", or is there a different technique altogether? I'm open to suggestions</p>
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