You're mixing up disk and RAM requirements when you talk about having twice the disk size. Solr does _NOT_ require twice the index size of RAM to optimize, it requires twice the size on _DISK_.
In terms of RAM requirements, you need to create an index, run realistic queries at the installation and measure. Best Erick On Tue, Apr 9, 2013 at 10:32 PM, bigjust <bigj...@lambdaphil.es> wrote: > > > >>> On 4/9/2013 7:03 PM, Furkan KAMACI wrote: >>> > These are really good metrics for me: >>> > You say that RAM size should be at least index size, and it is >>> > better to have a RAM size twice the index size (because of worst >>> > case scenario). >>> > On the other hand let's assume that I have a RAM size that is >>> > bigger than twice of indexes at machine. Can Solr use that extra >>> > RAM or is it a approximately maximum limit (to have twice size of >>> > indexes at machine)? >>> What we have been discussing is the OS cache, which is memory that >>> is not used by programs. The OS uses that memory to make everything >>> run faster. The OS will instantly give that memory up if a program >>> requests it. >>> Solr is a java program, and java uses memory a little differently, >>> so Solr most likely will NOT use more memory when it is available. >>> In a "normal" directly executable program, memory can be allocated >>> at any time, and given back to the system at any time. >>> With Java, you tell it the maximum amount of memory the program is >>> ever allowed to use. Because of how memory is used inside Java, >>> most long-running Java programs (like Solr) will allocate up to the >>> configured maximum even if they don't really need that much memory. >>> Most Java virtual machines will never give the memory back to the >>> system even if it is not required. >>> Thanks, Shawn >>> >>> > Furkan KAMACI <furkankam...@gmail.com> writes: > >> I am sorry but you said: >> >> *you need enough free RAM for the OS to cache the maximum amount of >> disk space all your indexes will ever use* >> >> I have made an assumption my indexes at my machine. Let's assume that >> it is 5 GB. So it is better to have at least 5 GB RAM? OK, Solr will >> use RAM up to how much I define it as a Java processes. When we think >> about the indexes at storage and caching them at RAM by OS, is that >> what you talk about: having more than 5 GB - or - 10 GB RAM for my >> machine? >> >> 2013/4/10 Shawn Heisey <s...@elyograg.org> >> > > 10 GB. Because when Solr shuffles the data around, it could use up to > twice the size of the index in order to optimize the index on disk. > > -- Justin
