Common usage of Arthas

Arthas Common usage of

watch

scene ： Look at the input parameters of the method , Just want to observe your call , Filter irrelevant calls

Parameters are basic reference types

@GetMapping("test1")
public String test1(String name,Integer age){
    
    return "ok";
}

In the use of watch When , An interface , If it is called frequently , Sometimes it's too late to see what you want to observe , Now I want to filter the specified name In order to see what I want to observe

#params[0], Represents the first parameter , And so on 
watch com.luo.test test1'{params,returnObj}' "params[0]=='zhangsan'"  -n 5  -x 3 

The parameter is one VO

@GetMapping("test2")
public String test2(Student student){
    
    return "ok";
}

@Data
 private class Student{
    
      private String name;
      private Integer age;
      private Addr addr;
 }

# Filter out last name luo Of the students 
watch com.luo.test test2 '{params,returnObj,throwExp}' "params[0].name=='luo'"  -n 5  -x 3 

trace

Method internal call path , And output the time consumption of each node on the method path

scene ： An interface reports an error in the production environment , But there are many interfaces if-else Branch , And because the log did not print out under certain circumstances , Just looking at the code, you can't know the method call stack , Can't accurately locate

# Capture a call ,-n Number of times 
$ trace --skipJDKMethod false demo.MathGame run  -n 1
Press Q or Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 60 ms.
`---ts=2019-12-04 00:44:41;thread_name=main;id=1;is_daemon=false;priority=5;TCCL=[email protected] `---[1.357742ms] demo.MathGame:run()
        +---[0.028624ms] java.util.Random:nextInt() #23
        +---[0.045534ms] demo.MathGame:primeFactors() #24 [throws Exception]
        +---[0.005372ms] java.lang.StringBuilder:<init>() #28
        +---[0.012257ms] java.lang.Integer:valueOf() #28
        +---[0.234537ms] java.lang.String:format() #28
        +---[min=0.004539ms,max=0.005778ms,total=0.010317ms,count=2] java.lang.StringBuilder:append() #28
        +---[0.013777ms] java.lang.Exception:getMessage() #28
        +---[0.004935ms] java.lang.StringBuilder:toString() #28
        `---[0.06941ms] java.io.PrintStream:println() #28 `---ts=2019-12-04 00:44:42;thread_name=main;id=1;is_daemon=false;priority=5;TCCL=sun.misc.Launcher$AppClassLoader@3d4eac69
    `---[3.030432ms] demo.MathGame:run() +---[0.010473ms] java.util.Random:nextInt() #23 +---[0.023715ms] demo.MathGame:primeFactors() #24 [throws Exception] +---[0.005198ms] java.lang.StringBuilder:<init>() #28 +---[0.006405ms] java.lang.Integer:valueOf() #28 +---[0.178583ms] java.lang.String:format() #28 +---[min=0.011636ms,max=0.838077ms,total=0.849713ms,count=2] java.lang.StringBuilder:append() #28 +---[0.008747ms] java.lang.Exception:getMessage() #28 +---[0.019768ms] java.lang.StringBuilder:toString() #28 `---[0.076457ms] java.io.PrintStream:println() #28

scene ： Look for the location that causes the slow response of the interface

# The display takes longer than 20ms Call path for 
$ trace demo.MathGame run '#cost > 20'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 41 ms.
`---ts=2018-12-04 01:12:02;thread_name=main;id=1;is_daemon=false;priority=5;TCCL=[email protected] `---[12.033735ms] demo.MathGame:run()
        +---[0.006783ms] java.util.Random:nextInt()
        +---[11.852594ms] demo.MathGame:primeFactors()
        `---[0.05447ms] demo.MathGame:print()

logger

Update the log level in real time

scene ： In the production environment , The log level of Key log information in the code is lower than that configured by the configuration file , Don't think of replacing file restart service

# Check the package or class logger Information 
[[email protected]]$ logger -n packageName/className
 name                                   org.springframework.web
 class                                  ch.qos.logback.classic.Logger
 classLoader                            sun.misc.Launcher$AppClassLoader@2a139a55
 classLoaderHash                        2a139a55
 level                                  null
 effectiveLevel                         INFO
 additivity                             true
 codeSource                             file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar

# View specific classes  classloader hashcode
[[email protected]]$ sc -d myClassName

# Modify the log level to debug
[[email protected]]$ logger -c 2a139a55 --name ROOT --level debug
update logger level success.

ognl expression

scene ： For example, I have changed the configuration , But I don't want to restart the service , What can I do to refresh the configuration cache in memory ？

Dynamic execution bean The method in

# Query this class , Find its classloader hash value 
[[email protected]]$ sc -d com.fy.CsdAndHjdCache
 class-info        com.fy.CsdAndHjdCache
 name              com.fy.CsdAndHjdCache
 isInterface       false
 isAnnotation      false
 isEnum            false
 isAnonymousClass  false
 isArray           false
 isLocalClass      false
 isMemberClass     false
 isPrimitive       false
 isSynthetic       false
 simple-name       CsdAndHjdCache
 modifier          public
 annotation
 interfaces
 super-class       +-java.lang.Object
                     [email protected]
                       +-sun.misc.Launcher$AppClassLoader@18b4aac2
                         +-sun.misc.Launcher$ExtClassLoader@32cf48b7
 classLoaderHash   69fbea59

# According to the class loader hash value , find spring The context of , Get... By context bean, Calling bean The method we want to call in , In this case , I want to re execute  init() Method 
[[email protected]]$ ognl -c 69fbea59 '#[email protected][email protected], #context.getBean("csdAndHjdCache").init()'

vmtool

Implement query memory object , mandatory GC And so on

scene ： For example, I have changed the configuration , But I don't want to restart the service , What can I do to refresh the configuration cache in memory ？

# Query this class , Find its classloader hash value 
[[email protected]]$ sc -d com.tq.questions.MyController
# Call the... Of this instance getA() Method 
[[email protected]]$ vmtool --action getInstances -c 18b4aac2  --className com.tq.questions.MyController --express 'instances[0].refreshConfigs()'

getInstances: action The returned result is bound to instances Variables on the , It's an array

The rest to be added ........