在sitepoint上看到一片文章，对比了aws rds、google cloud sql、cleardb、xeround四款云端mysql产品，包括它们的功能、价格、限制等因素。引用如下：
Even though all providers offer a hosted MySQL database, there are some differences. You will find limitations with:
- Xeround: Limitation in full MySQL compatibility, like ALTER table functions, log files and more. Seerelease notes. These limitations are mostly in place to make dynamic scalability possible.
- Google Cloud SQL: Limitation in full MySQL compatibility, and features like user defined functions and MySQL replication. SeeFAQ.
Amazon RDS for MySQL and Google Cloud SQL are pretty straightforward cloud-based MySQL instances, without much juice to it but with the added benefit of being in the cloud (when it comes to scaling up or down, easy cloning etc.). They simply allow you to host your database in their cloud infrastructure, with the above limitations. Amazon RDS for MySQL also has the option to have a replication standby in case of failure of your main database, and offers automated backups.
Selecting one of them depends mostly on which infrastructure you use to run your main applications. Amazon RDS would be the best fit if you host them on EC2 for example, because of low latencies. But the combo isn’t required, you can host a Google Cloud SQL database with an EC2 server.
Xeround en ClearDB take it up a notch, by providing high availability (100% uptime), easy backups and geo-distribution. Xeround tops it off with dynamic scalability for keeping up with size and throughput requirements. They both try to make it much easier for you to host your database in the cloud, without worrying about what happens when a node fails. They both run on Amazon AWS, as well as Rackspace Cloud and HP Cloud (Xeround) or Microsoft Azure (ClearDB).
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