You are indeed right about the open_file_cache, but you still left with a sync write(2) that can block, and blocking of eventloop is a major source of latency variance (unless you use Flash-based drives of course).
> On Aug 14, 2017, at 2:24 PM, Eran Kornblau <eran.kornb...@kaltura.com> wrote: > >> -----Original Message----- >> From: nginx-devel [mailto:nginx-devel-boun...@nginx.org] On Behalf Of Alexey >> Ivanov >> Sent: Monday, August 14, 2017 9:25 PM >> To: nginx-devel@nginx.org >> Subject: Re: Add support for buffering is scripted logs >> >> using syslog for that particular usecase seem way more elegant, >> customizable, and simple. As a side bonus you won't block event loop on vfs >> operations (open/write/close). >> > Thanks Alexey. > > Regarding the last point about performance, I ran a quick test, compared - > 1. Nginx writing to gzip access log - > access_log /var/log/nginx/access_log.gz main gzip flush=5m; > 2. Nginx writing to local rsyslog over UDP, which in turn writes to local > file - > access_log syslog:server=127.0.0.1 main; > 3. Nginx writing to remote rsyslog on the same LAN over UDP - > access_log syslog:server=192.168.11.94 main; > > Ran this command (execute 10 apache bench tests, take the median value): > (for i in `seq 1 10`; do ab -c 1000 -n 100000 127.0.0.1/alive.html > 2>/dev/null | grep '^ 50%' ; done) | awk '{print $2}' | xargs > > The nginx location being tested simply does 'return 200 "hello"'. > > Results are: > 1. 4 6 5 6 3 5 3 5 7 5 > 2. 6 7 5 7 6 7 7 7 7 7 > 3. 5 6 6 6 6 6 6 6 4 6 > > The numbers fluctuated a bit from one run to another (did it a few times), > but the overall trend was the same - > syslog is slower than having nginx write with gzip. The difference is not > dramatic, but it's visible. > This makes sense since with buffered write, nginx only has to perform a > syscall once every X messages, > most messages are written without any syscalls. > Regarding what you wrote about open/write/close, when using variables (even > before this patch), > it is possible to enable open file cache on log files, so you only have > 'write'. > > Eran > > _______________________________________________ > nginx-devel mailing list > nginx-devel@nginx.org > http://mailman.nginx.org/mailman/listinfo/nginx-devel
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