内容简介：Page Life Expectancy is a Perfmon counter that’s supposed to track how long pages stay in memory before they get flushed out to make room for other pages that are needed instead.Paul Randal has blogged this a few times, and rather than rehash ’em, I’d rath
Page Life Expectancy is a Perfmon counter that’s supposed to track how long pages stay in memory before they get flushed out to make room for other pages that are needed instead.
Paul Randal has blogged this a few times, and rather than rehash ’em, I’d rather point you to a couple of his roundups:
And layer in a few of my own observations for context:
Page Life Expectancy goes up 1 for each secondthat you’re not under memory pressure. Restart your SQL Server instance and watch PLE: it starts at 1, and goes up by 1 for each second of uptime. 5 minutes of uptime = PLE 300. For the first 5 minutes, it’s not like your server’s under memory pressure – it just woke up, for crying out loud. Give him a minute. Well, 15-20, I guess, because PLE is near useless during that time span.
Page Life Expectancy drops can be triggered by confusing operations.By default, any one running query can get a memory grant the size of 25% of your buffer pool. Run a few of those queries at the same time, and your buffer pool gets drained – but PLE doesn’t necessarily drop. However, the instant an unrelated query runs and needs to get data that isn’t cached in RAM, your PLE will drop catastrophically. Which queries are at fault? The queries getting large grants, or the queries doing reads? “Yes.”
Page Life Expectancy is a lagging indicator.Lagging indicators are something that tell you about an emergency long after the emergency has happened, and lagging indicators don’t recover quickly after the emergency is over. When you combine the above two problems – PLE only rising 1 per second, and PLE dropping at times that aren’t necessarily tied to the dropping buffer pool – then if you’re alerting based on low PLE numbers, you could have already missed the emergency. When you go log in and look for what long-running queries are running, it’s already too late. Instead, you should be using leading indicators: things that tell you a problem is coming up.
With that stuff in mind, I’ve removed the Page Life Expectancy warnings fromsp_BlitzFirst altogether. I think they’re distracting y’all from the real leading indicator, wait stats – and of course, sp_BlitzFirst shows that, so I’d rather focus your attention there.
以上就是本文的全部内容，希望本文的内容对大家的学习或者工作能带来一定的帮助，也希望大家多多支持 码农网
猜你喜欢:
本站部分资源来源于网络，本站转载出于传递更多信息之目的，版权归原作者或者来源机构所有，如转载稿涉及版权问题，请联系我们。
应用Rails进行敏捷Web开发
Dave Thomas, David Hansson等 / 林芷薰 / 电子工业出版社 / 2006-7 / 65.00元
这是第一本关于Ruby on Rails的著作。 全书主要内容分为两大部分。在“构建应用程序”部分中，读者将看到一个完整的“在线购书网站” 示例。在演示的过程中，作者真实地再现了一个完整的迭代式开发过程，让读者亲身体验实际应用开发中遇到的各种问题、以及Rails如何有效解决这些问题。在随后的“Rails框架”部分中，作者深入介绍了Rails框架的各个组成部分。尤为值得一提的是本部分的后几章......一起来看看 《应用Rails进行敏捷Web开发》 这本书的介绍吧!
