三样东西不要放数据库
Three things you should never put in your database

As I've said in a few talks, the best way to improve your systems is by first not doing "dumb things". I don't mean you or your development staff is "dumb", it's easy to overlook the implications of these types of decisions and not realize how bad they are for maintainability let alone scaling. As a consultant I see this stuff all of the time and I have yet to ever see it work out well for anyone.

Images, files, and binary data

Your database supports BLOBs so it must be a good idea to shove your files in there right? No it isn't! Hell it isn't even very convenient to use with many DB language bindings.

There are a few of problems with storing files in your database:
?read/write to a DB is always slower than a filesystem
?your DB backups grow to be huge and more time consuming
?access to the files now requires going through your app and DB layers

The last two are the real killers. Storing your thumbnail images in your database? Great now you can't use nginx or another lightweight web server to serve them up.

Do yourself a favor and store a simple relative path to your files on disk in the database or use something like S3 or any CDN instead.

Ephemeral data

Usage statistics, metrics, GPS locations, session data anything that is only useful to you for a short period of time or frequently changes. If you find yourself DELETEing an hour, day, or weeks worth of some table with a cron job, you're using the wrong tool for the job.

Use redis, statsd/graphite, Riak anything else that is better suited to that type of work load. The same advice goes for aggregations of ephemeral data that doesn't live for very long.

Sure it's possible to use a backhoe to plant some tomatoes in the garden, but it's far faster to grab the shovel in the garage than schedule time with a backhoe and have it arrive at your place and dig. Use the right tool(s) for the job at hand.

Logs

This one seems ok on the surface and the "I might need to use a complex query on them at some point in the future" argument seems to win people over. Storing your logs in a database isn't a HORRIBLE idea, but storing them in the same database as your other production data is.

Maybe you're conservative with your logging and only emit one log line per web request normally. That is still generating a log INSERT for every action on your site that is competing for resources that your users could be using. Turn up your logging to a verbose or debug level and watch your production database catch on fire!

Instead use something like Splunk, Loggly or plain old rotating flat files for your logs. The few times you need to inspect them in odd ways, even to the point of having to write a bit of code to find your answers, is easily outweighed by the constant resources it puts on your system.

But wait, you're a unique snowflake and your problem is SO different that it's ok for you to do one of these three. No you aren't and no it really isn't. Trust me.




导读：作者Frank Wiles发表了一篇博文，Frank Wiles曾在很多演讲里说过，改进你的系统的最好的方法是先避免做“蠢事”。并不是说你或你开发的东西“蠢”，只是有些决定很容易被人们忽略掉其暗含的牵连，认识不到这样做对系统维护尤其是系统升级带来多大的麻烦。作为一个顾问，像这样的事情我到处都能见到，我还从来没有见过做出这样的决定的人有过好的结果的。

图片，文件，二进制数据

既然数据库支持BLOB类型的数据，把文件塞进BLOB字段里一定没有错了！？错，不是这样的！别的先不提，在很多数据库语言里，处理大字段都不是很容易。

把文件存放在数据库里有很多问题：
?对数据库的读/写的速度永远都赶不上文件系统处理的速度
?数据库备份变的巨大，越来越耗时间
?对文件的访问需要穿越你的应用层和数据库层

这后两个是真正的杀手。把图片缩略图存到数据库里？很好，那你就不能使用nginx或其它类型的轻量级服务器来处理它们了。

给自己行个方便吧，在数据库里只简单的存放一个磁盘上你的文件的相对路径，或者使用S3或CDN之类的服务。

短生命期数据

使用情况统计数据，测量数据，GPS定位数据，session数据，任何只是短时间内对你有用，或经常变化的数据。如果你发现自己正在使用定时任务从某个表里删除有效期只有一小时，一天或数周的数据，那说明你没有找对正确的做事情的方法。使用redis， statsd/graphite， Riak，它们都是干这种事情更合适的工具。这建议也适用于对于收集那些短生命期的数据。

当然，用挖土