Also learned of https://github.com/aragozin/jvm-tools , which can generate flame graphs easily without requiring a restart with an agent, and works on openjdk+oracle.
On Mon, Oct 16, 2017 at 8:37 AM, Jeff Jirsa <jji...@gmail.com> wrote: > > I got some feedback last week that I should try this on Monday morning, so > let's see if we can nudge a few people into action this week. > > 3.0.15 and 3.11.1 are released. This is a dev list, so that shouldn't be a > surprise to anyone here - you should have seen the votes and release > notifications. The people working directly ON Cassandra every day are > probably very aware of the number and nature of fixes in those versions - > if you're not aware, the Change lists are HUGE, and some of the fixes are > VERY IMPORTANT. So this week's wrap-up is really a reflection on the size > of those two release changelogs. > > One of the advantages of the Cassandra project is the size of the user > base - I don't know if we have accurate counts (and some of the "surveys" > are laughable), but we know it's on the order of thousands (probably tens > of thousands) of companies, and some huge number of instances (not willing > to speculate here, we know it's at least in the hundreds of thousands, may > be well into the millions). Historically, the best stabilizer of a release > was people upgrading their unusual use cases, finding bugs that the > developers hadn't anticipated (and therefore tests didn't exist for those > edge cases), reporting them, and the next release would be slightly better > than the one before it. The chicken/egg problem here is pretty obvious, and > while a lot of us are spending a lot of time making things better, I want > to use this email to ask a favor (in 3 parts): > > 1) If you haven't tried 3.0 or 3.11 yet, please spin it up on a test > cluster. 3.11 would be better, 3.0 is ok too. It doesn't need to be a > thousand node cluster, most of the weird stuff we've seen in the post-3.0 > world deals with data, not cluster size. Grab some of your prod data if you > can, throw it into a test cluster, add a node/remove a node, tell us if it > doesn't work. > 2) Please run a stress workload against that test cluster, even if it's > 5-10 minutes. Purpose here is two-fold: like #1, it'll help us find some > edge cases we haven't seen before, but it'll also help us identify holes in > stress coverage. We have some tickets to add UDTs to stress ( > https://issues.apache.org/jira/browse/CASSANDRA-13260 ) and LWT ( > https://issues.apache.org/jira/browse/CASSANDRA-7960 ). Ideally your > stress profile should be more than "80% reads 20% writes" - try to actually > model your schema and query behavior. Do you use static columns? Do you use > collections? If you're unable to model your use case because of a > deficiency in stress, open a JIRA. If things break, open a JIRA. If it > works perfectly, I'm interested in seeing your stress yaml and results > (please send it to me privately, don't spam the list). > 3) If you're somehow not able to run stress because you don't have > hardware for a spare cluster, profiling your live cluster is also > incredibly useful. TLP has some notes on how to generate flame graphs - > https://github.com/thelastpickle/lightweight-java-profiler - I saw one > example from a cluster that really surprised me. There are versions and use > cases that we know have been heavily profiled, but there are probably > versions and use cases where nobody's ever run much in the way of > profiling. If you're running openjdk in prod, and you're able to SAFELY > attach a profiler to generate some flame graphs, please send those to me > (again, privately please, I don't think the whole list needs a copy). > > My hope in all of this is to build up a corpus of real world use cases > (and real current state via profiling) that we can leverage to make testing > and performance better going forward. If I get much in the way of response > to either of these, I'll try to send out a summary in next week's email). > > - Jeff > > >
