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 -------------------------------------------------------------------------
