to view HEAP Dump and Thread Dump : Heap dump analysis using Eclipse Memory Analyzer Tool (MAT) (cleantutorials.com)
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Threads with same state (fastthread.io)
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Shallow Heap and Retained Heap
Gc Log Report :Brilliant GC graphs, metrics and KPIs (gceasy.io)
Heap Memory Leak and OutofMemory
Note : Heap and GC are decide the Performance of JVM.
Available Memory : Total Memory - Used Memory
or Available Memory = (Free Memory + buffer or Cache Memeory)
Heap is the area where the Objects and References are Stored.
References :
- Soft
- Weak
- Strong
- Panther
All the Object related data is stored in Heap Area.
Every JVM having only one Heap Area.
Object Information, Object runtime data and all the Instance variables information. These can be accessed by multiple Memory.
Heap dump analysis using Eclipse Memory Analyzer Tool (MAT)
Every JVM having only one Heap Area.
Object Information, Object runtime data and all the Instance variables information. These can be accessed by multiple Memory.
Heap dump analysis using Eclipse Memory Analyzer Tool (MAT)
Heap Dump to find the Memory Leaks and it is state of Objects.
By Using Heap dump we can able to find
By Using Heap dump we can able to find
Memory LeaksLarge Object AllocationInefficient Memory usage
A heap dump is a snapshot of all the Java objects that exist in the heap space. The heap dump file is usually stored with .hprof extension.
(hprof :- HEAP Profiling Tool or CPU Profiling Tool)
Note :- When memory usage exceeds beyond XMX, then we will get JVM outofmemory Exception
Why and When should I take the Heap dump?
If your Java application is taking up more memory than you expected or
(hprof :- HEAP Profiling Tool or CPU Profiling Tool)
Note :- When memory usage exceeds beyond XMX, then we will get JVM outofmemory Exception
Why and When should I take the Heap dump?
If your Java application is taking up more memory than you expected or
your Java application crashed with OutOfMemoryError.
Whenever the Available Memory goes Down
Some sudden Failures in the Application. Eg: High CPU Utilization, Suddenly Response Time increase, etc...
Analyzing the heap dump will lead us to the root cause of the anomaly.
Using the heap dump we can find details like the memory usage per class, number of objects per class, etc. We can also go into fine details and find out the amount of memory retained by a single Java object in the application. These details can help us pinpoint the actual code that is causing the memory leak issues.
How do you analyze very large Heap dumps?
Usually analyzing heap dump takes even more memory than the actual heap dump size and this may be problematic if you are trying to analyze heap dump from a large server on your development machine. For instance, a server may have crashed with a heap dump of size 24 GB and your local machine may only have 16 GB of memory. Therefore, tools like MAT, Jhat won’t be able to load the heap dump file. In this case, you should either analyze the heap dump on the same server machine which doesn’t have memory constraint or use live memory sampling tools provided by VisualVM.
How to take a Heap dump of your running Java Application
There are several ways to take a heap dump. We will talk about the 3 easiest ways to do it.
Using the heap dump we can find details like the memory usage per class, number of objects per class, etc. We can also go into fine details and find out the amount of memory retained by a single Java object in the application. These details can help us pinpoint the actual code that is causing the memory leak issues.
How do you analyze very large Heap dumps?
Usually analyzing heap dump takes even more memory than the actual heap dump size and this may be problematic if you are trying to analyze heap dump from a large server on your development machine. For instance, a server may have crashed with a heap dump of size 24 GB and your local machine may only have 16 GB of memory. Therefore, tools like MAT, Jhat won’t be able to load the heap dump file. In this case, you should either analyze the heap dump on the same server machine which doesn’t have memory constraint or use live memory sampling tools provided by VisualVM.
How to take a Heap dump of your running Java Application
There are several ways to take a heap dump. We will talk about the 3 easiest ways to do it.
Using jmap command
Using jcmd command on terminal
Using JMX Console
Using the JVisualVM tool
Identifying HeapDumpOnOutOfMemory
Using HotSpotDiagnosticMBean by writing a program
Note :- When memory usage exceeds beyond XMX, then we will get JVM outofmemory Exception
1. jmap Command to generate the Heap Dump
jmap -dump:live,file=<file-name + .hprof> <pid> or
jmap -dump:[live],format=b,file=<file-path> <pid>
live:- This parameter is optional. If set, it prints all those objects that have active references.
format = b , which means the heap dump file is in binary format. It is not necessary to set this parameter.
2. Using jcmd command on terminal
This command sends a request to the JVM to generate a heap dump. One of its parameters is GC.heap_dump. It is as shown below:
jcmd <pid> GC.heap_dump <file-path>
<pid> - Process id of java process
<file-path> - Path where the heap dump is to be generated
3. VisualVM to generate the Heap Dump
Visual VM makes it very easy to take a heap dump running on your local machine. The following steps can be used to generate heap dump using VisualVM
a. Start Visual VM and connect your local Java Application to it.
b. Under the Monitor Tab, click on Heap Dump
c. After clicking on the heap dump you will be redirected to a new tab from which you can find out the location of your heap dump.
4. JConsole to generate the Heap dump
1. Connect your application to JConsole.
2. Switch to MBeans tab and select com.sun.management > HotSpotDiagnostic > Operations > dumpHeap.
3. Before clicking on the dumpHeap function, set the parameters p0, p1 described below.steps to take heap dump using java jconsole
a. The parameter p0 is the location and the name of the heap dump file. Ensure that you add the “.hprof” extension at the end of the file name.
b. The parameter p1, if set to true, performs a GC before dumping the heap so that only live objects are present in the heap dump.
5. Identifying HeapDumpOnOutOfMemory
It is ideal to capture heap dumps when an application experiences java.lang.OutOfMemoryError. Heap dumps help identify live objects sitting in the memory and the percentage of memory it occupies.
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<file-path>
While running your java application when this system property is set, JVM takes a snapshot of the heap dump when it encounters OutOfMemoryError.
https://www.geeksforgeeks.org/understanding-outofmemoryerror-exception-java/
Which tools can be used to analyze the heap dump or open the .hprof file?
Once you have the heap dump the next step is to analyze it using a tool. There are multiple paid and equally good open source tools available to analyze the Heap dump. Memory Analyzer (MAT) is one of the best open-source tool that can be used as a plugin with Eclipse or as a standalone application if you don’t have Eclipse IDE installed. Apart from MAT, you can use Jhat, VisualVM. However, in this post, we will discuss the features provided with MAT.
Downloading the Memory Analyzer (MAT)
There are two ways to use the Memory Analyzer tool.
Integrating MAT plugin with Eclipse
1. Open Eclipse IDE and select Help > Eclipse Marketplace.
2. Search for Memory Analyzer and install it. memory analyzer tool (MAT) installation steps using Eclipse IDE
3. Restart Eclipse and the plugin is ready to be used.
Downloading the standalone version of Eclipse MAT
1. Download and install the Java Development Kit.
2. Download the install standalone MAT application from this link.
3. After extracting the package open MemoryAnalyzer application to start using the standalone version of MAT.
Eclipse memory analyzer installation steps
Loading Heap dump file in Eclipse MAT
We will be analyzing the heap dump generated by this Java application. The memory leak in the application
is discussed in depth in this tutorial. And the screenshots posted below are from the MAT plugin used with
Eclipse IDE.
The steps to load the heap dump are as follows.
1. Open Eclipse IDE or the standalone MAT Tool.
2. From the toolbar, Select Files > Open File from the dropdown menu.
3. Open the heap dump file with the extension .hprof and you should see the overview page as shown below.
loading a heap dump using memory analyzer
We will go through some of the important tools like Histogram, Dominator Tree and Leak Suspect report
which can be used to identify memory leaks.
Histogram
Histogram lists all the different classes loaded in your Java Application at the time of heap dump. It also lists
the number of objects per class along with the shallow and retained heap size. Using the histogram,
it is hard to identify which object is taking the most memory. However, we can easily identify which class
type holds the largest amount of memory. For instance, in the screenshot below byte array holds the
largest amount of memory. But, we cannot identify which object actually holds that byte array.
Shallow Heap v/s Retained Heap
Shallow Heap is the size of the object itself. For instance, in the screenshot below byte array itself holds
the largest amount of memory. Retained Heap is the size of the object itself as well as the size of all the
objects retained in it. For instance, in the screenshot below the DogShelter object itself holds a size of
16 bytes. However, it has a retained heap size of more than 305Mb which means it likely holds the byte
array which contributes to the very large retained heap size.
eclipse memory analyzer histogram tab
Finally, from the Histogram, we infer that the problem suspect is byte[] which is retained by the object of
class DogShelter or Dog.
Dominator Tree
The dominator tree of the Java objects allows you to easily identify object holding the largest chunk of
memory. For instance, we can see from the snipped below that the Main Thread object holds the largest
memory. On collapsing the main thread tree we can see that the instance of class DogShelter holds a
hashmap holding over 300Mb of memory.
Dominotart tree is useful when you have a single object that is eating up a large amount of memory.
The Dominator tree wouldn’t make much sense if multiple small objects are leading to a memory leak.
In that case, it would be better to use the Histogram to find out the instances of classes that consume the
most amount of memory.
eclipse memory analyzer dominator tree tab
From the Dominator Tree, we infer that the problem suspect is the DogShelter class.
Duplicate Classes
The duplicate class tab will list down the classes that are loaded multiple times. If you are using ClassLoaders in your code, you can use the Duplicate Classes to ensure that the code is functioning properly and classes
are not loaded multiple times.
Leak Suspect
Finally, the Leak suspect report runs a leak suspect query that analyzes the Heap dump and tries to find the
memory leak. For non-trivial memory leaks, the Leak suspect query may not be able to identify the memory
leak and it’s up to the developer with the knowledge of the program to pinpoint the leak using the tools
discussed above.
Since we had a very trivial memory leak, the inference that we derived manually using Histogram and
Dominator Tree is the same as the inference from the leak suspect report as seen below.
Using jcmd command on terminal
Using JMX Console
Using the JVisualVM tool
Identifying HeapDumpOnOutOfMemory
Using HotSpotDiagnosticMBean by writing a program
Note :- When memory usage exceeds beyond XMX, then we will get JVM outofmemory Exception
1. jmap Command to generate the Heap Dump
jmap -dump:live,file=<file-name + .hprof> <pid> or
jmap -dump:[live],format=b,file=<file-path> <pid>
live:- This parameter is optional. If set, it prints all those objects that have active references.
format = b , which means the heap dump file is in binary format. It is not necessary to set this parameter.
- file =<file-path> indicates where the heap dump file will be generated.
2. Using jcmd command on terminal
This command sends a request to the JVM to generate a heap dump. One of its parameters is GC.heap_dump. It is as shown below:
jcmd <pid> GC.heap_dump <file-path>
<pid> - Process id of java process
<file-path> - Path where the heap dump is to be generated
3. VisualVM to generate the Heap Dump
Visual VM makes it very easy to take a heap dump running on your local machine. The following steps can be used to generate heap dump using VisualVM
a. Start Visual VM and connect your local Java Application to it.
b. Under the Monitor Tab, click on Heap Dump
c. After clicking on the heap dump you will be redirected to a new tab from which you can find out the location of your heap dump.
4. JConsole to generate the Heap dump
1. Connect your application to JConsole.
2. Switch to MBeans tab and select com.sun.management > HotSpotDiagnostic > Operations > dumpHeap.
3. Before clicking on the dumpHeap function, set the parameters p0, p1 described below.steps to take heap dump using java jconsole
a. The parameter p0 is the location and the name of the heap dump file. Ensure that you add the “.hprof” extension at the end of the file name.
b. The parameter p1, if set to true, performs a GC before dumping the heap so that only live objects are present in the heap dump.
5. Identifying HeapDumpOnOutOfMemory
It is ideal to capture heap dumps when an application experiences java.lang.OutOfMemoryError. Heap dumps help identify live objects sitting in the memory and the percentage of memory it occupies.
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<file-path>
While running your java application when this system property is set, JVM takes a snapshot of the heap dump when it encounters OutOfMemoryError.
https://www.geeksforgeeks.org/understanding-outofmemoryerror-exception-java/
Which tools can be used to analyze the heap dump or open the .hprof file?
Once you have the heap dump the next step is to analyze it using a tool. There are multiple paid and equally good open source tools available to analyze the Heap dump. Memory Analyzer (MAT) is one of the best open-source tool that can be used as a plugin with Eclipse or as a standalone application if you don’t have Eclipse IDE installed. Apart from MAT, you can use Jhat, VisualVM. However, in this post, we will discuss the features provided with MAT.
Downloading the Memory Analyzer (MAT)
There are two ways to use the Memory Analyzer tool.
Integrating MAT plugin with Eclipse
1. Open Eclipse IDE and select Help > Eclipse Marketplace.
2. Search for Memory Analyzer and install it. memory analyzer tool (MAT) installation steps using Eclipse IDE
3. Restart Eclipse and the plugin is ready to be used.
Downloading the standalone version of Eclipse MAT
1. Download and install the Java Development Kit.
2. Download the install standalone MAT application from this link.
3. After extracting the package open MemoryAnalyzer application to start using the standalone version of MAT.
Eclipse memory analyzer installation steps
Loading Heap dump file in Eclipse MAT
We will be analyzing the heap dump generated by this Java application. The memory leak in the application
is discussed in depth in this tutorial. And the screenshots posted below are from the MAT plugin used with
Eclipse IDE.
The steps to load the heap dump are as follows.
1. Open Eclipse IDE or the standalone MAT Tool.
2. From the toolbar, Select Files > Open File from the dropdown menu.
3. Open the heap dump file with the extension .hprof and you should see the overview page as shown below.
loading a heap dump using memory analyzer
We will go through some of the important tools like Histogram, Dominator Tree and Leak Suspect report
which can be used to identify memory leaks.
Histogram
Histogram lists all the different classes loaded in your Java Application at the time of heap dump. It also lists
the number of objects per class along with the shallow and retained heap size. Using the histogram,
it is hard to identify which object is taking the most memory. However, we can easily identify which class
type holds the largest amount of memory. For instance, in the screenshot below byte array holds the
largest amount of memory. But, we cannot identify which object actually holds that byte array.
Shallow Heap v/s Retained Heap
Shallow Heap is the size of the object itself. For instance, in the screenshot below byte array itself holds
the largest amount of memory. Retained Heap is the size of the object itself as well as the size of all the
objects retained in it. For instance, in the screenshot below the DogShelter object itself holds a size of
16 bytes. However, it has a retained heap size of more than 305Mb which means it likely holds the byte
array which contributes to the very large retained heap size.
eclipse memory analyzer histogram tab
Finally, from the Histogram, we infer that the problem suspect is byte[] which is retained by the object of
class DogShelter or Dog.
Dominator Tree
The dominator tree of the Java objects allows you to easily identify object holding the largest chunk of
memory. For instance, we can see from the snipped below that the Main Thread object holds the largest
memory. On collapsing the main thread tree we can see that the instance of class DogShelter holds a
hashmap holding over 300Mb of memory.
Dominotart tree is useful when you have a single object that is eating up a large amount of memory.
The Dominator tree wouldn’t make much sense if multiple small objects are leading to a memory leak.
In that case, it would be better to use the Histogram to find out the instances of classes that consume the
most amount of memory.
eclipse memory analyzer dominator tree tab
From the Dominator Tree, we infer that the problem suspect is the DogShelter class.
Duplicate Classes
The duplicate class tab will list down the classes that are loaded multiple times. If you are using ClassLoaders in your code, you can use the Duplicate Classes to ensure that the code is functioning properly and classes
are not loaded multiple times.
Leak Suspect
Finally, the Leak suspect report runs a leak suspect query that analyzes the Heap dump and tries to find the
memory leak. For non-trivial memory leaks, the Leak suspect query may not be able to identify the memory
leak and it’s up to the developer with the knowledge of the program to pinpoint the leak using the tools
discussed above.
Since we had a very trivial memory leak, the inference that we derived manually using Histogram and
Dominator Tree is the same as the inference from the leak suspect report as seen below.
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