trace

Track methods calling stack trace and print the time cost in each call.

Parameters

Name	Specification
class-pattern	pattern for the class name
method-pattern	pattern for the method name
condition-express	condition expression
[E]	turn on regx matching while the default is wildcards matching
[n:]	calling times
#cost	time cost

F.Y.I

1. any valid OGNL expression as "{params,returnObj}" supported;
2. filter by time cost as trace *StringUtils isBlank '#cost>100'; calling stack with only time cost higher than 100ms will be printed.

Attention:

1. #cost can be used in watch/stack/trace;
2. using #cost in Arthas 3.0 instead of $cost.
3. trace can help to locate the performance lurking issue but only level-one method invoking considered.

Advanced:

• Critical fields in expression
• Special usage
• OGNL official guide

Usage

A demo:

    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("a");
        list.add("b");

        List<String> list2 = new ArrayList<String>();
        list2.add("c");
        list2.add("d");

        int len = add(list, list2);
    }

    private static int add(List<String> list, List<String> list2) {
        int i = 10;
        while (i >= 0) {
            try {
                hehe(i);
            } catch (Throwable t) {
                t.printStackTrace();
            }
            i--;
        }

        list.addAll(list2);
        return list.size();
    }

    private static void hehe(int i) {
        if (i == 0) {
            throw new RuntimeException("ZERO");
        }
    }

Tracing down method add:

$ trace com.alibaba.sample.petstore.web.store.module.screen.ItemList add params.length==2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 144 ms.
`---Tracing...
    `---[2ms]com.alibaba.sample.petstore.web.store.module.screen.ItemList:add()
        +---[0,0,0ms,11]com.alibaba.sample.petstore.web.store.module.screen.ItemList:hehe() [throws Exception]
        +---[1ms]java.lang.Throwable:printStackTrace()
        +---[0ms]java.util.List:addAll()
        `---[0ms]java.util.List:size()

Filtering by time cost:

$ trace com.alibaba.sample.petstore.web.store.module.screen.ItemList execute #cost>4
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 159 ms.
trace com.alibaba.sample.petstore.web.store.module.screen.ItemList execute #cost>4
`---thread_name=http-nio-8080-exec-5;id=2c;is_daemon=true;priority=5;TCCL=com.taobao.pandora.boot.embedded.tomcat.TomcatEmbeddedWebappClassLoader
    `---[8.866586ms] com.alibaba.sample.petstore.web.store.module.screen.ItemList:execute()
        +---[2.847106ms] com.alibaba.sample.petstore.biz.StoreManager:getAllProductItems()
        +---[0.765544ms] com.alibaba.sample.petstore.dal.dao.ProductDao:getProductById()
        +---[0.021204ms] com.alibaba.sample.petstore.dal.dataobject.Product:getCategoryId()
        +---[1.341532ms] com.alibaba.sample.petstore.dal.dao.CategoryDao:getCategoryById()
        `---[min=0.005428ms,max=0.094064ms,total=0.105228ms,count=3] com.alibaba.citrus.turbine.Context:put()

Only the calling trace of the time cost higher than 4mspresented now.

F.Y.I

1. like JProfile and other similar commercial software, you can trace down the specified method calling stack with time cost in Arthas;
2. there will be some overhead using trace but not much;
3. the time cost is an instructive clue for troubleshooting, which means it’s not that accurate ignoring the cost it itself causes; the deeper or more the call is, the worse accuracy the time cost will be;
4. [0,0,0ms,11]xxx:yyy() [throws Exception]，the same method calling aggregated into one line here while throws Exception indicates there is an exception.