SUN has recently clarify the issue regarding "unsupported unless you pay" for the G1 garbage collector. Here is the updated release of Java 6 update 14: http://java.sun.com/javase/6/webnotes/6u14.html
G1 will be part of Java 7, fully supported without pay. The version included in Java 6 update 14 is a beta release. Since it is beta, SUN does not recommend using it unless you have a support contract because as with any beta software there will be bugs. Non paying customers may very well have to wait for the official version in Java 7 for bug fixes. Here is more info on the G1 garbage collector: http://java.sun.com/javase/technologies/hotspot/gc/g1_intro.jsp Bill On Sat, Oct 3, 2009 at 1:28 PM, Mark Miller <markrmil...@gmail.com> wrote: > Another option of course, if you're using a recent version of Java 6: > > try out the beta-ish, unsupported unless you pay, G1 garbage collector. > I've only recently started playing with it, but its supposed to be much > better than CMS. Its supposedly got much better throughput, its much > better at dealing with fragmentation issues (CMS is actually pretty bad > with fragmentation come to find out), and overall its just supposed to > be a very nice leap ahead in GC. Havn't had a chance to play with it > much myself, but its supposed to be fantastic. A whole new approach to > generational collection for Sun, and much closer to the "real time" GC's > available from some other vendors. > > Mark Miller wrote: > > siping liu wrote: > > > >> Hi, > >> > >> I read pretty much all posts on this thread (before and after this one). > Looks like the main suggestion from you and others is to keep max heap size > (-Xmx) as small as possible (as long as you don't see OOM exception). This > brings more questions than answers (for me at least. I'm new to Solr). > >> > >> > >> > >> First, our environment and problem encountered: Solr1.4 (nightly build, > downloaded about 2 months ago), Sun JDK1.6, Tomcat 5.5, running on > Solaris(multi-cpu/cores). The cache setting is from the default > solrconfig.xml (looks very small). At first we used minimum JAVA_OPTS and > quickly run into the problem similar to the one orignal poster reported -- > long pause (seconds to minutes) under load test. jconsole showed that it > pauses on GC. So more JAVA_OPTS get added: "-XX:+UseConcMarkSweepGC > -XX:+UseParNewGC -XX:ParallelGCThreads=8 -XX:SurvivorRatio=2 > -XX:NewSize=128m -XX:MaxNewSize=512m -XX:MaxGCPauseMillis=200", the thinking > is with mutile-cpu/cores we can get over with GC as quickly as possibe. With > the new setup, it works fine until Tomcat reaches heap size, then it blocks > and takes minutes on "full GC" to get more space from "tenure generation". > We tried different Xmx (from very small to large), no difference in long GC > time. We never run into OOM. > >> > >> > > MaxGCPauseMillis doesnt work with UseConcMarkSweepGC - its for use with > > the Parallel collector. That also doesnt look like a good survivorratio. > > > >> > >> > >> Questions: > >> > >> * In general various cachings are good for performance, we have more RAM > to use and want to use more caching to boost performance, isn't your > suggestion (of lowering heap limit) going against that? > >> > >> > > Leaving RAM for the FileSystem cache is also very important. But you > > should also have enough RAM for your Solr caches of course. > > > >> * Looks like Solr caching made its way into tenure-generation on heap, > that's good. But why they get GC'ed eventually?? I did a quick check of Solr > code (Solr 1.3, not 1.4), and see a single instance of using WeakReference. > Is that what is causing all this? This seems to suggest a design flaw in > Solr's memory management strategy (or just my ignorance about Solr?). I > mean, wouldn't this be the "right" way of doing it -- you allow user to > specify the cache size in solrconfig.xml, then user can set up heap limit in > JAVA_OPTS accordingly, and no need to use WeakReference (BTW, why not > SoftReference)?? > >> > >> > > Do you see concurrent mode failure when looking at your gc logs? ie: > > > > 174.445: [GC 174.446: [ParNew: 66408K->66408K(66416K), 0.0000618 > > secs]174.446: [CMS (concurrent mode failure): 161928K->162118K(175104K), > > 4.0975124 secs] 228336K->162118K(241520K) > > > > That means you have still getting major collections with CMS, and you > > don't want that. You might try kicking GC off earlier with something > > like: -XX:CMSInitiatingOccupancyFraction=50 > > > >> * Right now I have a single Tomcat hosting Solr and other applications. > I guess now it's better to have Solr on its own Tomcat, given that it's > tricky to adjust the java options. > >> > >> > >> > >> thanks. > >> > >> > >> > >> > >> > >>> From: wun...@wunderwood.org > >>> To: solr-user@lucene.apache.org > >>> Subject: RE: Solr and Garbage Collection > >>> Date: Fri, 25 Sep 2009 09:51:29 -0700 > >>> > >>> 30ms is not better or worse than 1s until you look at the service > >>> requirements. For many applications, it is worth dedicating 10% of your > >>> processing time to GC if that makes the worst-case pause short. > >>> > >>> On the other hand, my experience with the IBM JVM was that the maximum > query > >>> rate was 2-3X better with the concurrent generational GC compared to > any of > >>> their other GC algorithms, so we got the best throughput along with the > >>> shortest pauses. > >>> > >>> Solr garbage generation (for queries) seems to have two major > components: > >>> per-request garbage and cache evictions. With a generational collector, > >>> these two are handled by separate parts of the collector. Per-request > >>> garbage should completely fit in the short-term heap (nursery), so that > it > >>> can be collected rapidly and returned to use for further requests. If > the > >>> nursery is too small, the per-request allocations will be made in > tenured > >>> space and sit there until the next major GC. Cache evictions are almost > >>> always in long-term storage (tenured space) because an LRU algorithm > >>> guarantees that the garbage will be old. > >>> > >>> Check the growth rate of tenured space (under constant load, of course) > >>> while increasing the size of the nursery. That rate should drop when > the > >>> nursery gets big enough, then not drop much further as it is increased > more. > >>> > >>> After that, reduce the size of tenured space until major GCs start > happening > >>> "too often" (a judgment call). A bigger tenured space means longer > major GCs > >>> and thus longer pauses, so you don't want it oversized by too much. > >>> > >>> Also check the hit rates of your caches. If the hit rate is low, say > 20% or > >>> less, make that cache much bigger or set it to zero. Either one will > reduce > >>> the number of cache evictions. If you have an HTTP cache in front of > Solr, > >>> zero may be the right choice, since the HTTP cache is cherry-picking > the > >>> easily cacheable requests. > >>> > >>> Note that a commit nearly doubles the memory required, because you have > two > >>> live Searcher objects with all their caches. Make sure you have > headroom for > >>> a commit. > >>> > >>> If you want to test the tenured space usage, you must test with real > world > >>> queries. Those are the only way to get accurate cache eviction rates. > >>> > >>> wunder > >>> > >>> > >> > >> _________________________________________________________________ > >> Bing™ brings you maps, menus, and reviews organized in one place. Try > it now. > >> > http://www.bing.com/search?q=restaurants&form=MLOGEN&publ=WLHMTAG&crea=TEXT_MLOGEN_Core_tagline_local_1x1 > >> > >> > > > > > > > > > -- > - Mark > > http://www.lucidimagination.com > > > > >
