This FAQ entry and the linked document provide a pretty good explanation: http://wiki.apache.org/cassandra/FAQ#mmap
By the way, you should almost always turn off swap. On Thu, Nov 17, 2011 at 1:16 AM, Jaesung Lee <ljsk...@gmail.com> wrote: > I am running 7 nodes cassandra(v1.0.2) cluster. > I am putting 20K rows per sec to the cluster. > This cluster has 1 KS, 3CFs. > Each CF has 4-5 secondary indices. > > After I'v run for 1 week, nodes use swap memory. > I changed disk-access-mode to index_only or standard. > I got strange memory results. > > using mmap: > VIRT: 566g RES: 36g SHR:12g > standard disk access mode > VIRT:24.7g RES: 24g SHR:68m > > > I allocated 24g memory for JVM heap. > > I have some questions about mmap. > It is easy to analyze standard disk access mode's memory result. > > I know cassandra use huge virtual memory for mmap I/O and each mmaped > addresses are mapped to indexed file not swap memory. > > But, I don't understand why cassandra use shared memory, if using mmap I/O. > > Are there some documents that explain this situation? > > -- > Jaesung Lee > Sent with Sparrow <http://www.sparrowmailapp.com/?sig> > > -- Tyler Hobbs DataStax <http://datastax.com/>
