Greetings! I have a question on optimal # of unicorn worker processes. We are running Unicorn 4.3.1 + Rails 3.2.6 (without threading), on ruby 1.9.3-p194, hosted on SmartOS/Joyent. At the moment, unicorns are configured to start 30 worker processes. I know this is a lot, and I am going to reduce this number. But in trying to figure out what is a more appropriate number of workers to run, I noticed something interesting that I couldn''t explain. If I look at the process table on each machine (see top output below), I notice that some unicorn processes are heavily used (and have accumulated longer CPU times, as well as have grown their RAM usage since boot time), but other processes (at the bottom of the top output) appear to potentially not having been used at all. There are several processes with RSS size of 143Mb, which I believe is unicorn size before it processes any requests. What I am gathering from this, is that only 16 unicorn processes are actually processing requests, while the rest are just sitting there idle. Is this expected behavior? This Joyent SmartMachine can burst up to 8 cores. Given that our web requests spend only 80% of their time in ruby, I figured we could run 10 unicorn processes for maximum efficiency. However seeing that 16 are actually used I am curious whether 16 is actually a better number. Any suggestions appreciated! load averages: 2.07, 1.97, 2.09; up 14+01:56: 58 processes: 53 sleeping, 5 on cpu CPU states: 77.1% idle, 18.2% user, 4.7% kernel, 0.0% iowait, 0. Memory: 8192M phys mem, 3157M free mem, 16G total swap, 11G free sw PID USERNAME LWP PRI NICE SIZE RES STATE TIME CPU COMMAND 24800 wanelo 18 59 0 337M 313M sleep 17:21 2.05% ruby 24788 wanelo 18 59 0 223M 200M cpu/14 16:34 3.18% ruby 24787 wanelo 18 59 0 221M 197M sleep 14:55 1.89% ruby 24776 wanelo 18 59 0 217M 193M cpu/2 18:17 3.45% ruby 24804 wanelo 18 59 0 216M 192M cpu/8 7:54 0.33% ruby 24785 wanelo 18 59 0 211M 187M sleep 14:33 0.75% ruby 24783 wanelo 10 59 0 209M 185M sleep 16:09 2.16% ruby 24775 wanelo 18 59 0 205M 181M sleep 5:24 0.03% ruby 24777 wanelo 10 59 0 205M 181M cpu/11 3:53 1.54% ruby 24799 wanelo 18 59 0 204M 179M sleep 0:42 0.00% ruby 24803 wanelo 18 59 0 202M 177M sleep 2:28 0.35% ruby 24802 wanelo 3 59 0 195M 168M sleep 1:45 0.01% ruby 24778 wanelo 3 59 0 192M 165M sleep 1:06 0.01% ruby 24801 wanelo 3 59 0 189M 162M sleep 0:50 0.01% ruby 24798 wanelo 3 59 0 188M 161M sleep 0:30 0.00% ruby 24797 wanelo 3 59 0 187M 159M sleep 0:19 0.00% ruby --- unicorns below this line do not appear to be used 24795 wanelo 3 59 0 173M 142M sleep 0:08 0.00% ruby 24792 wanelo 3 59 0 172M 142M sleep 0:07 0.00% ruby 24779 wanelo 3 59 0 172M 143M sleep 0:05 0.00% ruby 24796 wanelo 3 59 0 172M 142M sleep 0:12 0.00% ruby 24790 wanelo 3 59 0 172M 142M sleep 0:06 0.00% ruby 24793 wanelo 3 59 0 172M 142M sleep 0:06 0.00% ruby 24781 wanelo 3 59 0 172M 142M sleep 0:05 0.00% ruby 24791 wanelo 3 59 0 172M 142M sleep 0:04 0.00% ruby 24794 wanelo 3 58 0 172M 142M sleep 0:10 0.00% ruby 24784 wanelo 3 59 0 172M 142M sleep 0:04 0.00% ruby
Konstantin Gredeskoul <kig at wanelo.com> wrote:> Greetings! > > I have a question on optimal # of unicorn worker processes. > > We are running Unicorn 4.3.1 + Rails 3.2.6 (without threading), on > ruby 1.9.3-p194, hosted on SmartOS/Joyent. > > At the moment, unicorns are configured to start 30 worker processes. I > know this is a lot, and I am going to reduce this number. But in > trying to figure out what is a more appropriate number of workers to > run, I noticed something interesting that I couldn''t explain. > > If I look at the process table on each machine (see top output below), > I notice that some unicorn processes are heavily used (and have > accumulated longer CPU times, as well as have grown their RAM usage > since boot time), but other processes (at the bottom of the top > output) appear to potentially not having been used at all. There are > several processes with RSS size of 143Mb, which I believe is unicorn > size before it processes any requests. > > What I am gathering from this, is that only 16 unicorn processes are > actually processing requests, while the rest are just sitting there > idle. > > Is this expected behavior?It''s not _unexpected_ if your load is low. The OS scheduler does the load balancing itself as unicorn uses non-blocking accept(). The scheduler may choose busier processes because they''re likely to be hotter in cache/memory. So you''re probably getting better performance than if you had perfectly balanced traffic. Another possible explanation is something is killing some workers (timeout, or crash buts, check stderr logs to confirm). But even in a situation where workers never die, it''s perfectly normal to see workers that never/rarely serve traffic.> This Joyent SmartMachine can burst up to 8 cores. Given that our web > requests spend only 80% of their time in ruby, I figured we could run > 10 unicorn processes for maximum efficiency. However seeing that 16 > are actually used I am curious whether 16 is actually a better number.It depends what your app is waiting on. The only rule is your machine should not be swap thrashing under peak load. Extra workers won''t be detrimental as long as you: 1) have enough memory 2) have enough backend resources (e.g DB connections) I know of deployments that run 30 processes/core because the app spends much time waiting on slow HTTP/DB requests[1] But if your app is completely bound by resources local to a machine (no external DB/HTTP/memcached/redis/etc requests), then a 1:1 worker:core (or even 1:1 worker:disk) relationship will work, too. [1] Arguably a multi-threaded or non-blocking server such as Rainbows! would be most efficient of machine resources if you''re waiting on HTTP calls, but the developers decided human time was more important and did not want to worry about thread-safety.
Thanks Eric! Appreciate well thought out answers. We are actually using Rainbows also, in an project where long server-side HTTP calls are part of the application design and are necessary, and it''s working out really well. Our main web app mostly spends it''s time in CPU cycles serving web pages (about 80% of the request time), and 20% in database operations. Thanks again K On Tue, Aug 21, 2012 at 2:11 AM, Eric Wong <normalperson at yhbt.net> wrote:> Konstantin Gredeskoul <kig at wanelo.com> wrote: >> Greetings! >> >> I have a question on optimal # of unicorn worker processes. >> >> We are running Unicorn 4.3.1 + Rails 3.2.6 (without threading), on >> ruby 1.9.3-p194, hosted on SmartOS/Joyent. >> >> At the moment, unicorns are configured to start 30 worker processes. I >> know this is a lot, and I am going to reduce this number. But in >> trying to figure out what is a more appropriate number of workers to >> run, I noticed something interesting that I couldn''t explain. >> >> If I look at the process table on each machine (see top output below), >> I notice that some unicorn processes are heavily used (and have >> accumulated longer CPU times, as well as have grown their RAM usage >> since boot time), but other processes (at the bottom of the top >> output) appear to potentially not having been used at all. There are >> several processes with RSS size of 143Mb, which I believe is unicorn >> size before it processes any requests. >> >> What I am gathering from this, is that only 16 unicorn processes are >> actually processing requests, while the rest are just sitting there >> idle. >> >> Is this expected behavior? > > It''s not _unexpected_ if your load is low. The OS scheduler does the > load balancing itself as unicorn uses non-blocking accept(). The > scheduler may choose busier processes because they''re likely to be > hotter in cache/memory. > > So you''re probably getting better performance than if you had perfectly > balanced traffic. > > Another possible explanation is something is killing some workers > (timeout, or crash buts, check stderr logs to confirm). But even in a > situation where workers never die, it''s perfectly normal to see workers > that never/rarely serve traffic. > >> This Joyent SmartMachine can burst up to 8 cores. Given that our web >> requests spend only 80% of their time in ruby, I figured we could run >> 10 unicorn processes for maximum efficiency. However seeing that 16 >> are actually used I am curious whether 16 is actually a better number. > > It depends what your app is waiting on. > > The only rule is your machine should not be swap thrashing under > peak load. > > Extra workers won''t be detrimental as long as you: > 1) have enough memory > 2) have enough backend resources (e.g DB connections) > > I know of deployments that run 30 processes/core because the app spends > much time waiting on slow HTTP/DB requests[1] > > But if your app is completely bound by resources local to a machine (no > external DB/HTTP/memcached/redis/etc requests), then a 1:1 worker:core > (or even 1:1 worker:disk) relationship will work, too. > > > > [1] Arguably a multi-threaded or non-blocking server such as Rainbows! > would be most efficient of machine resources if you''re waiting on HTTP > calls, but the developers decided human time was more important and > did not want to worry about thread-safety. > _______________________________________________ > Unicorn mailing list - mongrel-unicorn at rubyforge.org > http://rubyforge.org/mailman/listinfo/mongrel-unicorn > Do not quote signatures (like this one) or top post when replying-- Konstantin Gredeskoul CTO :: Wanelo Inc cell: (415) 265 1054