My backing store is file-based. In any case, thanks to you both -- I have ordered some more RAM and will see what happens.
Martin > > > On Wed, Jan 27, 2010 at 12:23 AM, Michael Fischer <mich...@dynamine.net>wrote: > >> On Tue, Jan 26, 2010 at 7:23 PM, Martin Goldman <m...@mgoldman.com> wrote: >> >> I'm running Varnish on a box with 4GB RAM. There are hundreds of thousands >>> of objects being served, and I'm certain that they don't all fit in that >>> relatively meager amount of RAM. I understand that Varnish's model dictates >>> that the kernel will be trusted to use virtual memory as necessary if the >>> cached objects don't fit in RAM. I have a few questions about this: >>> >>> 1. How can you tell whether your Varnish objects fit in RAM? >>> >> >> You can't guarantee that they will unless you set your cache size at or >> below the amount of RAM you have installed. >> >> >>> 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? >>> >> >> Technically, it's "go out and buy as much RAM as it will take to avoid >> being swamped by paging". But yes. >> >> >>> 3. I noticed tonight that my machine was using a few hundred megs of >>> swap space, which I've never seen happen before. Varnish is the only >>> non-system service running on this box. My understanding was that Varnish >>> would get only as much RAM as was available and then send the overflow into >>> the file-backed virtual memory. If that's the case, though, then why is swap >>> space being used? Is this just a side effect of how the kernel allocates >>> memory, or is something else going on here? >>> >> >> Is your backing store file-based, or malloc-based? If the latter, that >> would explain the swap space being consumed. Or, as Darryl said, the >> housekeeping overhead of a VERY large file-backed cache could make the >> Varnish process very large. >> >> --Michael >> > >
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