Talk about your GC Tuning ideas ?

I find , At present, a lot of external data on G1 Most of the introductions still stay in JDK 7 Or earlier implementations , Many conclusions already have large deviations , Even some of the past GC Option is no longer recommended . therefore , Today I will choose the new version JDK Default in G1 GC Explain in detail as a key point , And I will from the perspective of tuning practice , Analyze typical scenarios and tuning ideas . Now let's update this knowledge .

My question for you today is , Talk about your GC Tuning ideas ？

Typical answer

• When it comes to tuning , This must be for a specific scenario 、 Something for a specific purpose , about GC For tuning , First, you need to know what the tuning goal is ？ From a performance point of view , It usually focuses on three aspects , Memory footprint （footprint）、 Time delay （latency） And throughput （throughput）, In most cases, tuning will focus on one or both of these goals , There are few situations where three different perspectives can be taken into account . Of course , In addition to the usual three aspects above , Other things may need to be considered as well GC Related scenes , for example ,OOM It may also be related to unreasonable GC Related parameters related to ; perhaps , Application startup speed requirements ,GC It will also be a consideration
• The basic tuning ideas can be summarized as ：
  • Understand application requirements and problems , Set tuning goals . hypothesis , We developed an application service , But I find that occasionally there will be performance jitter , There was a long service pause . Evaluate the user's acceptable response time and business volume , Simplify the goal to , hope GC Try to limit the pause to 200ms within , And ensure a certain standard of throughput
  • master JVM and GC The state of , Positioning specific issues , I'm sure there are GC The need for tuning . There are many ways , such as , adopt jstat Wait for tools to check GC And so on , Can be opened GC journal , Or use the diagnostic tools provided by the operating system . for example , By tracking GC journal , You can find out if GC A long pause occurred at a specific time , This leads to untimely application response
  • There's a need to think about , Select the GC Whether the type conforms to our application characteristics , If it is , What are the specific problems , yes Minor GC Too long , still Mixed GC When there is an abnormal pause ; If not , Consider what type to switch to , Such as CMS and G1 Are more focused on low latency GC Options
  • Through the analysis to determine the specific adjustment parameters or hardware and software configuration
  • Verify that the tuning objectives are met , If you get there , That is, you can consider ending the tuning ; otherwise , Repeat the analysis 、 adjustment 、 Verify the process

Test point analysis

• Today's expedition GC The tuning problem is JVM A fundamental aspect of tuning , quite a lot JVM Tuning requirements , Will eventually be implemented in GC On or related to tuning , What I offer is a common idea ：
  • Really quickly locate and solve specific problems , Still need to be right JVM and GC Mastery of knowledge , And the summary of actual tuning experience , Sometimes it's even intuitive judgment from experience
  • The interviewer may continue to ask real questions about the project , If you can understand 、 Briefly introduce its context , Then describe the diagnosis idea and tuning practice process , It will be a good bonus