Well, we've seen a Cassandra process swap out 500 MB on a Linux OS with plenty of RAM, so I was just curious as why the OS thinks it should use the swap at all.
2013/3/13 karim duran <karim.du...@gmail.com>: > I agree with Edward Capriolo, > Even when swap is enabled on your system, swaping rarely occurs on OS > today...(except for very loaded systems). > > But, take care that some 32 bits system kernels allows only 2^32 bits memory > mapped file length ( ~ 2 Go ). > It could be a limitation for NoSQL databases. It's the case for MongoDB on > 32 bits OS. > > I don't know how to avoid swaping if Cassandra exceeds these limitation when > this case occurs. > > > 2013/3/13 Edward Capriolo <edlinuxg...@gmail.com> >> >> You really can not control what the OS-swaps out. java has other memory >> usage outside the heap, and native memory. best to turn swap off. Swap is >> kinda old school anyway at this point. It made sense when machines had 32MB >> RAM. >> >> Keeping your read 95th percentile low is mostly about removing deviations >> that cause requests to slow down, swap is one of the things that cause >> fluctuation becuase it is not predictable. >> >> On Wed, Mar 13, 2013 at 10:39 AM, Fredrik >> <fredrik.l.stigb...@sitevision.se> wrote: >>> >>> I've got a question regarding understanding the recomendation to disable >>> swap. >>> Since Cassandra uses mlockall to lock the heap in RAM what is the reason >>> for disabling swap? >>> My guess is that is has to do with memory mapped files but as of my >>> understanding, accessing pages of >>> memory mapped files, those pages are never put in swap since they're >>> backed by files on disk and the OS >>> writes those pages to the memory mapped file instead of swap. >>> We've seen on Cassandra installations on Linux with swap enabled that >>> parts of the java process is swaped out and increasing. >>> So what's swaped out? >>> >>> Regards >>> /Fredrik >>> >>> >>> >>> >> > -- Fredrik Larsson Stigbäck SiteVision AB Vasagatan 10, 107 10 Örebro 019-17 30 30
