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copied!<p>I'd really, really, suggest stay with MySQL (or a RDBMS) until you fully understand the situation.</p> <p>I have no idea how much performance or much data you plan on using, but 30M rows is not very many. </p> <p>If you need to optimise certain range scans, you can do this with (for example) InnoDB by choosing a (implicitly clustered) primary key judiciously, and/or denormalising where necessary.</p> <p>But like most things, make it work first, then fix performance problems you detect in your performance test lab on production-grade hardware.</p> <hr> <p>EDIT:Some other points:</p> <ul> <li>key/value database such as Cassandra, Voldermort etc, do not generally support secondary indexes</li> <li>Therefore, you cannot do a CREATE INDEX</li> <li>Most of them also don't do range scans (even on the main index) because they're using hashing to implement partitioning (which they mostly do).</li> <li>Therefore they also don't do range expiry (DELETE FROM tbl WHERE ts < NOW() - INTERVAL 30 DAYS)</li> <li>Your application must do ALL of this itself or manage without it; secondary indexes are really the killer</li> <li>ALTER TABLE ... ADD INDEX takes quite a long time in e.g. MySQL with a large table, but at least you don't have to write much code to do it. In a "nosql" database, it will also take a long time BUT also you have to write heaps and heaps of code to maintain the new secondary index, expire it correctly, AND modify your queries to use it.</li> </ul> <p>In short... you can't use a key/value database as a shortcut to avoid ALTER TABLE.</p>

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