I'm developing a high-volume web application, where part of it is a MySQL database of discussion posts that will need to grow to 20M+ rows, smoothly.
I was originally planning on using MyISAM for the tables (for the built-in fulltext search capabilities), but the thought of the entire table being locked due to a single write operation makes me shutter. Row-level locks make so much more sense (not to mention InnoDB's other speed advantages when dealing with huge tables). So, for this reason, I'm pretty determined to use InnoDB.
The problem is... InnoDB doesn't have built-in fulltext search capabilities.
Should I go with a third-party search system? Like Lucene(c++) / Sphinx? Do any of you database ninjas have any suggestions/guidance? LinkedIn's zoie (based off Lucene) looks like the best option at the moment... having been built around realtime capabilities (which is pretty critical for my application.) I'm a little hesitant to commit yet without some insight...
(FYI: going to be on EC2 with high-memory rigs, using PHP to serve the frontend)
I can vouch for MyISAM fulltext being a bad option - even leaving aside the various problems with MyISAM tables in general, I've seen the fulltext stuff go off the rails and start corrupting itself and crashing MySQL regularly.
A dedicated search engine is definitely going to be the most flexible option here - store the post data in MySQL/innodb, and then export the text to your search engine. You can set up a periodic full index build/publish pretty easily, and add real-time index updates if you feel the need and want to spend the time.
Lucene and Sphinx are good options, as is Xapian, which is nice and lightweight. If you go the Lucene route don't assume that Clucene will better, even if you'd prefer not to wrestle with Java, although I'm not really qualified to discuss the pros and cons of either.