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80 lines
4.0 KiB
Markdown
80 lines
4.0 KiB
Markdown
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---
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title: "Debugging by Jattach"
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hide_title: true
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---
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We have installed jattach in Docker image of datahub-gms, datahub-mae-consumer, datahub-mce-consumer
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and datahub-frontend to facilitating troubleshooting in a production environment.
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# Introduction to Jattach
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Jattach is a utility to send commands to a JVM process via Dynamic Attach mechanism.
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Supported commands:
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- load : load agent library
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- properties : print system properties
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- agentProperties : print agent properties
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- datadump : show heap and thread summary
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- threaddump : dump all stack traces (like jstack)
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- dumpheap : dump heap (like jmap)
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- inspectheap : heap histogram (like jmap -histo)
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- setflag : modify manageable VM flag
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- printflag : print VM flag
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- jcmd : execute jcmd command
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# Use examples
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Jattach is a All-in-one **jmap + jstack + jcmd + jinfo** functionality in a single tiny program.
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The scenarios where these commands were previously used can now be replaced with jattach.
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## Example 1: Dump heap
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The jattach dumpheap command is typically used in the following scenarios:
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- Memory leak analysis: When an application experiences memory leaks or abnormal memory growth, the jattach dumpheap
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command is used to generate a heap dump file for further analysis and identification of the memory leak causes.
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- Memory analysis: By generating a heap dump file, various memory analysis tools such as Eclipse Memory Analyzer and
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VisualVM can be utilized to analyze objects, reference relationships, and memory usage within the heap. This helps
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identify potential performance issues and optimization opportunities.
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- Troubleshooting: When encountering frequent Full GCs, memory out-of-memory errors, or other memory-related issues,
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generating a heap dump file provides additional information for troubleshooting and debugging purposes.
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- Performance optimization: By analyzing the heap dump file, it becomes possible to identify which objects in the
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application consume a significant amount of memory. This information can be used for targeted performance optimizations,
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such as reducing object creation or optimizing cache usage.
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It's important to note that generating a heap dump file can have an impact on the performance of the application.
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Therefore, caution should be exercised when using it in a production environment, ensuring sufficient resources and
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permissions are available for the operation.
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The command is as follows:
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```bash
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jattach <pid> dumpheap /tmp/heap.bin
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```
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## Example 2: Dump thread
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The jattach threaddump command is typically used in the following scenarios:
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- Deadlock analysis: When an application experiences deadlocks or thread contention issues, the jattach threaddump
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command is used to generate a thread dump file. It provides the current thread's stack trace information, helping to
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identify the code paths and lock contention causing the deadlock.
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- Thread troubleshooting: When threads in an application encounter exceptions, long blocking times, excessive CPU usage,
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or other issues, generating a thread dump file provides detailed information about each thread's state, stack trace, and
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resource usage. This helps with troubleshooting and analysis.
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- Performance analysis: By generating a thread dump file, it becomes possible to understand the thread activity, call
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paths, and resource contention within the application. This aids in identifying potential performance bottlenecks and
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concurrency issues.
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- Monitoring and diagnostics: Regularly generating thread dump files can be used to monitor the health of an application
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and provide historical data for subsequent diagnostics. This helps gain a better understanding of the application's
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behavior and performance.
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It's important to note that generating a thread dump file may impact the performance of the application. Therefore,
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caution should be exercised when using it in a production environment, ensuring sufficient resources and permissions
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are available for the operation.
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The command is as follows:
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```bash
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jattach <pid> threaddump -l > /tmp/jstack.out
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```
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