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*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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