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 > > [image: Inline image 1] > > 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 >>> >>> [image: Inline image 1] >>> >>> ta...@tok-media.com >>> Tel: +972 2 6409736 >>> Mob: +972 54 8356490 >>> Fax: +972 2 5612956 >>> >>> >>> >>> >> >
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