Anecdotal evidence typically agrees that 2.1 is faster than 2.0 (our experience was anywhere from 20-60%, depending on workload).
However, it’s not necessarily true that everything behaves exactly the same – in particular, memtables are different, commitlog segment handling is different, and GC params may need to be tuned differently for 2.1 than 2.0. When the system is busy, what’s it actually DOING? Cassandra exposes a TON of metrics – have you plugged any into a reporting system to see what’s going on? Is your latency due to pegged cpu, iowait/disk queues or gc pauses? My colleagues spent a lot of time validating different AWS EBS configs (video from reinvent at https://www.youtube.com/watch?v=1R-mgOcOSd4), 2.1 was faster in almost every case, but you’re using an instance size I don’t believe we tried (too little RAM to be viable in production). c3.2xl only gives you 15G of ram – most “performance” based systems want 2-4x that (people running G1 heaps usually start at 16G heaps and leave another 16-30G for page cache), you’re running fairly small hardware – it’s possible that 2.1 isn’t “as good” on smaller hardware. (I do see your domain, presumably you know all of this, but just to be sure): You’re using c3, so presumably you’re using EBS – are you using GP2? Which volume sizes? Are they the same between versions? Are you hitting your iops limits? Running out of burst tokens? Do you have enhanced networking enabled? At load, what part of your system is stressed? Are you cpu bound? Are you seeing GC pauses hurt latency? Have you tried changing memtable_allocation_type -> offheap objects (available in 2.1, not in 2.0)? Tuning gc_grace is weird – do you understand what it does? Are you overwriting or deleting a lot of data in your test (that’d be unusual)? Are you doing a lot of compaction? From: "Peddi, Praveen" Reply-To: "user@cassandra.apache.org" Date: Wednesday, January 6, 2016 at 11:41 AM To: "user@cassandra.apache.org" Subject: Slow performance after upgrading from 2.0.9 to 2.1.11 Hi, We have upgraded Cassandra from 2.0.9 to 2.1.11 in our loadtest environment with pretty much same yaml settings in both (removed unused yaml settings and renamed few others) and we have noticed performance on 2.1.11 is worse compared to 2.0.9. After more investigation we found that the performance gets worse as we increase replication factor on 2.1.11 where as on 2.0.9 performance is more or less same. Has anything architecturally changed as far as replication is concerned in 2.1.11? All googling only suggested 2.1.11 should be FASTER than 2.0.9 so we are obviously doing something different. However the client code, load test is all identical in both cases. Details: Nodes: 3 ec2 c3.2x large R/W Consistency: QUORUM Renamed memtable_total_space_in_mb to memtable_heap_space_in_mb and removed unused properties from yaml file. We run compaction aggressive compaction with low gc_grace (15 mins) but this is true for both 2.0.9 and 2.1.11. As you can see, all p50, p90 and p99 latencies stayed with in 10% difference on 2.0.9 when we increased RF from 1 to 3, where as on 2.1.11 latencies almost doubled (especially reads are much slower than writes). # Nodes RF# of rows2.0.92.1.11 READ P50P90P99P50P90P99 314503065947474258491085 3345035863487770812742642 WRITE 3110268017937131196 3310319618446166468 Any pointers on how to debug performance issues will be appreciated. Praveen
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