Hi! I am running 1.0.8. So if I understand correctly both Memtable and Key cache are stored in the heap. (I don't have row cache) SSTables are mapped to operating system's virtual memory system, so if I increase heap I guess there will be less memory for this?
I have seen the changes in 1.1, but we are not there yet. Thanks, *Tamar Fraenkel * Senior Software Engineer, TOK Media [image: Inline image 1] ta...@tok-media.com Tel: +972 2 6409736 Mob: +972 54 8356490 Fax: +972 2 5612956 On Wed, Aug 22, 2012 at 9:23 AM, Thomas Spengler < thomas.speng...@toptarif.de> wrote: > Thats not right > > since 1.1.X it will used > > my hint: > take a look at > > commitlog_total_space_in_mb > it seams to be maped to off heap usage > the fix for taking the whole off-heap-memory is included in 1.1.3 > > the next parameter you have to take a look > > disk_access_mode: mmap_index_only > #disk_access_mode: auto > #disk_access_mode: standard > > and the third > > row_cache_provider: > > the default has changed from 1.0.X to 1.1.X > the new one takes off-heap-cache (with and also without jna) > > Regards > Tom > > On 08/22/2012 06:37 AM, aaron morton wrote: > >> "How do I know if my off-heap memory is not used?" > > > > > > If you are using the default memory mapped file access memory not used > by the cassandra JVM will be used to cache files. > > > > Cheers > > > > ----------------- > > Aaron Morton > > Freelance Developer > > @aaronmorton > > http://www.thelastpickle.com > > > > On 22/08/2012, at 5:17 AM, Tamar Fraenkel <ta...@tok-media.com> wrote: > > > >> Much appreciated. > >> What you described makes a lot of sense from all my readings :) > >> > >> Thanks! > >> Tamar Fraenkel > >> Senior Software Engineer, TOK Media > >> > >> <tokLogo.png> > >> > >> ta...@tok-media.com > >> Tel: +972 2 6409736 > >> Mob: +972 54 8356490 > >> Fax: +972 2 5612956 > >> > >> > >> > >> > >> > >> On Tue, Aug 21, 2012 at 6:43 PM, Alain RODRIGUEZ <arodr...@gmail.com> > wrote: > >> You're welcome. I'll answer to your new questions but keep in mind that > I am not a cassandra commiter nor even a cassandra specialist. > >> > >> "you mean that key cache is not in heap? I am using cassandra 1.0.8 and > I was under the expression it was, see > http://www.datastax.com/docs/1.0/operations/tuning, Tuning Java Heap > Size." > >> > >> > http://www.datastax.com/dev/blog/whats-new-in-cassandra-1-0-improved-memory-and-disk-space-management > >> > >> If I understood this correctly, It seems that only the row cache is > off-heap. So it's not an issue for us as far as we don't use row cache. > >> > >> "I thought that key-cache-size + 1GB + memtable space should not exceed > heap size. Am I wrong?" > >> > >> I don't know if this is a good formula. Datastax gives it so it > shouldn't be that bad :). However I would say that "key-cache-size + 1GB + > memtable space" should not exceed 0.75 * Max Heap (where 0.75 is > flush_largest_memtables_at). I keep default key-cache (which is 5% of max > heap if I remember well on 1.1.x) and default memtable space (1/3 of max > heap). I have enlarged my heap from 2 to 4 GB because I had some memory > pressure (sometimes the Heap Used was greater than 0.75 * Max Heap) > >> > >> "WARN [ScheduledTasks:1] 2012-08-20 12:31:46,506 GCInspector.java (line > 145) Heap is 0.7704251937535934 full. You may need to reduce memtable > and/or cache sizes. Cassandra will now flush up to the two largest > memtables to free up memory. Adjust flush_largest_memtables_at threshold > in cassandra.yaml if you don't want Cassandra to do this automatically" > >> > >> This message is the memory pressure I was talking about just above. > >> > >> "How do I know if my off-heap memory is not used?" > >> > >> Well, if you got no row cache and your server is only used as a > Cassandra node, I'm quite sure you can tune your heap to get 4GB. I guess a > htop or any memory monitoring system is able to tell you how much your > memory is used. > >> > >> I hope I didn't tell you too much bullshits :p. > >> > >> Alain > >> > >> 2012/8/21 Tamar Fraenkel <ta...@tok-media.com> > >> Thanks for you prompt response. Please see follow up questions below > >> Thanks!!! > >> > >> > >> > >> Tamar Fraenkel > >> Senior Software Engineer, TOK Media > >> > >> <tokLogo.png> > >> > >> ta...@tok-media.com > >> Tel: +972 2 6409736 > >> Mob: +972 54 8356490 > >> Fax: +972 2 5612956 > >> > >> > >> > >> > >> > >> On Tue, Aug 21, 2012 at 12:57 PM, Alain RODRIGUEZ <arodr...@gmail.com> > wrote: > >> I have the same configuration and I recently change my > cassandra-sh.yaml to : > >> > >> MAX_HEAP_SIZE="4G" > >> HEAP_NEWSIZE="200M" > >> > >> I guess it depends on how much you use the cache (which is now in the > off-heap memory). > >> > >> you mean that key cache is not in heap? I am using cassandra 1.0.8 and > I was under the expression it was, see > http://www.datastax.com/docs/1.0/operations/tuning, Tuning Java Heap Size. > >> I thought that key-cache-size + 1GB + memtable space should not exceed > heap size. Am I wrong? > >> > >> > >> I don't use row cache and use the default key cache size. > >> Me too, I have Key Cache capacity of 200000 for all my CFs. Currently > if my calculations are correct I have about 1.4GB of key cache. > >> > >> I have no more memory pressure nor OOM. > >> I don't see OOM, but I do see messages like the following in my logs: > >> INFO [ScheduledTasks:1] 2012-08-20 12:31:46,506 GCInspector.java (line > 122) GC for ParNew: 219 ms for 1 collections, 1491982816 used; max is > 1937768448 > >> WARN [ScheduledTasks:1] 2012-08-20 12:31:46,506 GCInspector.java (line > 145) Heap is 0.7704251937535934 full. You may need to reduce memtable > and/or cache sizes. Cassandra will now flush up to the two largest > memtables to free up memory. Adjust flush_largest_memtables_at threshold > in cassandra.yaml if you don't want Cassandra to do this automatically > >> > >> > >> > >> I think that if your off-heap memory is unused, it's better enlarging > the heap (with a max limit of 8GB) > >> > >> How do I know if my off-heap memory is not used? > >> > >> Hope this will help. > >> > >> Alain > >> > >> 2012/8/21 Tamar Fraenkel <ta...@tok-media.com> > >> Hi! > >> I have a question regarding Cassandra heap size. > >> Cassandra calculates heap size in cassandra-env.sh according to the > following algorythm > >> # set max heap size based on the following > >> # max(min(1/2 ram, 1024MB), min(1/4 ram, 8GB)) > >> # calculate 1/2 ram and cap to 1024MB > >> # calculate 1/4 ram and cap to 8192MB > >> # pick the max > >> > >> So, for > >> system_memory_in_mb=7468 > >> half_system_memory_in_mb=3734 > >> quarter_system_memory_in_mb=1867 > >> This will result in > >> max(min(3734,1024), min(1867,8000)) = max(1024,1867)=1867MB or in other > words 1/4 of RAM. > >> > >> In http://www.datastax.com/docs/1.0/operations/tuning it says: > "Cassandra's default configuration opens the JVM with a heap size of 1/4 of > the available system memory (or a minimum 1GB and maximum of 8GB for > systems with a very low or very high amount of RAM). Heapspace should be a > minimum of 1/2 of your RAM, but a maximum of 8GB. The vast majority of > deployments do not benefit from larger heap sizes because (in most cases) > the ability of Java 6 to gracefully handle garbage collection above 8GB > quickly diminishes." > >> If I understand this correctly, this means it is better if my heap size > will be 1/2 of RAM, 3734MB. > >> I am running on EC2 m1.large instance (7.5 GB memory, 4 EC2 Compute > Units (2 virtual cores with 2 EC2 Compute Units each)). > >> My system seems to be suffering from lack of memory, and I should > probably increase heap or (and?) reduce key cache size. > >> > >> Would you recommend changing the heap to half RAM? > >> > >> If yes, should I hard-code it in acassandra-env.sh? > >> > >> Thanks! > >> > >> Tamar Fraenkel > >> Senior Software Engineer, TOK Media > >> > >> <tokLogo.png> > >> > >> ta...@tok-media.com > >> Tel: +972 2 6409736 > >> Mob: +972 54 8356490 > >> Fax: +972 2 5612956 > >> > >> > >> > >> > >> > >> > >> > > > > > > > -- > Thomas Spengler > Chief Technology Officer > ------------------------------------------------------------------------ > > TopTarif Internet GmbH, Pappelallee 78-79, D-10437 Berlin > Tel.: (030) 2000912 0 | Fax: (030) 2000912 100 > thomas.speng...@toptarif.de | www.toptarif.de > > Amtsgericht Charlottenburg, HRB 113287 B > Geschäftsführer: Dr. Rainer Brosch, Dr. Carolin Gabor > ------------------------------------------------------------------------- >
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