How much memory does my Oracle instance use? How much memory do my database connections use?
These are questions that can help with capacity planning of your server’s Physical and Virtual memory. There are several write ups out there on the web that attempt to address these questions. From what I could gather from them, there is only one truly good way to tell exactly how much memory is currently in use by an oracle instance (or any other system, http, mysql, etc), as well as the average memory usage for oracle dedicated connection processes.
This technique makes use of the “pmap” command. This command displays the real current memory usage of a process broken down by memory segment types. By parsing the output of pmap, we can make several useful calculations. Note that this command is available for Linux, Solaris and HP-UX servers. It is also apparently available on AIX as “procmap”. Read the rest of this entry . . .
I gave this talk at the UKOUG, and I have received a few requests to post the slides online. Instead of just posting the PowerPoint I took some time to give the presentation again (internally here at Pythian) and this time we recorded the session and we are posting it here in a variety of formats. This is a bit of a departure from the typical Pythian Goodies, in that it is scripted, and there is a lot of content here in the whitepaper, but there hasn’t been a Goodie in a while so why not!
I’d love to hear from you, so please feel free to ask any follow-up questions to this post in the comments.
Abstract
Do I have enough memory? Why is my free memory so low? Am I swapping to disk? Can I increase my SGA (db cache) size? Can I add another instance to this server? Are my system resources used optimally? These are all questions that often haunt DBAs. This presentation is The Answer. It covers in detail the different types of memory, how to monitor memory, and how to optimally use it with Oracle. Multiple examples in the presentation demonstrate how certain actions on the database side cause different memory areas to be allocated and used on the OS side. Key underlying differences in operating systems approaches to managing memory will be highlighted, with special attention given to Linux, Solaris, and Windows. Using Linux as an example throughout, this presentation explains how to effectively use tools such as “top”, “vmstat” and “/proc/meminfo” to look into into a system’s allocation and use of memory.
Below you should see a flash video with me giving the session.
And below you will find the complete contents of the whitepaper. This is intended to be a good overall reference resource for how memory works in Oracle, using Linux as an example.
