Memory usage

Poul-Henning Kamp phk at
Tue Feb 2 13:34:53 CET 2010

In message <24a219a51001261923n40146083yb221aac2cadbcff8 at>, Marti
n Goldman writes:

>1. How can you tell whether your Varnish objects fit in RAM?

If you start seeing disk-activity, they do not fit.

>2. If I have objects residing in virtual memory, to what extent will my
>performance be adversely affected? If I want my site to be fast, do I
>basically need to go out and buy as much RAM as it will take so that virtual
>memory isn't needed?

Well, the impact is the necessary disk-I/O to bring the object into

Getting more RAM is one solution, but if your working set is much
larger than 4G, getting a SSD disk instead might be a better investment.

>3. I noticed tonight that my machine was using a few hundred megs of swap

Yes, varnish will force inactive programs (inetd, getty, sendmail etc)
out to swap so it can get at the RAM.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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