Performance: All Things Work Together

Introduction: Gatling is a light weighted load generator. Though it is 'load test as code', sometimes it is hard to debug. Especially when there is lack of documentation and tutorial. I run into an issue when upgrading from 2.3.1 to 3.0.2. The error message is not very helpful. Here I will show this case to illustrate an upgrading issue, as well is tricks to print out some debug information. Some Debug Tricks: According to  gatling document , you can print out debug information in 2 ways. change conf/logback.xml to DEBUG/TRACE for logger name="io.gatling.http.engine.response" This generates too much information and my tests times out.  Use println in exec. This is more flexible and can prints the exact information I need. How ever I would like to put the debug messages in a separate file. Here is an example: val file = System.getProperty("file", "/tmp/debug_cookie.out") val scn = scenario(myReadScenario) .during (myDur...

System Stats when I/O Might Be the Bottleneck: 1. iostat -x <delay> <repeats> shows the io for each device: Device: rrqm/s   wrqm/s   r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util sdb     0.00   121.67    0.00  454.67  0.00  7696.00    33.85      0.06    0.12    0.00    0.12   0.04    1.97 sda     0.00     3.00    0.00   5.33   0.00   857.33    321.50     0.07   12.31    0.00   12.31   2.12   1.13 avg-cpu:  %user   %nice %system %iowait  %steal   %idle           3.58    0.00    0.69    0.08    ...

Introduction: In this post, I will compare the commonly used java profilers(Java Flight Recorder, Solaris Studio, FlameGraph and VTune) in terms of usage, overhead and data presented. The observation is based on default collections. If more data are collected, the observations may change. I run SPECjbb2015 at a prefixed IR for 5 minutes. During this 5 minutes, I collect system level statistics, SPECjbb2015 console output, and collect profiles for 60 seconds (except for VTune). Software and Hardware  JDK8u144 Ubuntu 16.04.1 LTS Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz, 2 Socket, 8 cores per Socket Java Flight Recorder(JFR): JFR gives Java level profile, and some JVM internal statistics.  There are 2 ways to start JFR. From Java command line, or from jcmd. Command Line:  From command line -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=parameter1=value1[,parameter2=value2]   Parameters for -XX:S...

G1GC Performance Tuning Parameters In this post, I will list some common observations from G1GC logs, and the parameters you can try to tune the performance. To print GC logs, please refer to  my blog about how to print gc logs . Threads Related In JDK9, with -Xlog:gc*=info, or -Xlog:gc+cpu=info, you can get log entry like: [12.420s][info][gc,cpu      ] GC(0) User=0.14s Sys=0.03s Real=0.02s This can give you some indication about the cpu utilization for the GC pause. For example, this entry indicates for this gc pause, total user-cpu is 0.14s, wall time is 0.02s, and system time is 0.03s. The ratio of User/Real could be used as an estimation of number of gc threads you need. For this case, 18 gc threads should be good. If you see long termination time,  User/Real less than the gc threads, you can try to reduce the number of gc threads. Here is a list of threads related parameters: Name ...