The document describes memory usage pattern in JVM at OOM, and identifies rules for an early detection system which can alert about impending OOM error, and hence a crash.
JVM memory metrics and rules for detecting likely OOM caused crashAjit Bhingarkar
The document describes memory usage pattern in JVM at OOM, and identifies rules for an early detection system which can alert about impending OOM error, and hence a crash.
GARBAGE COLLECTOR Automatic garbage collection is the process of looking at heap memory, identifying which objects are in use and which are not, and deleting the unused objects. An in use object, or a referenced object, means that some part of your program still maintains a pointer to that object. An unused object, or unreferenced object, is no longer referenced by any part of your program. So the memory used by an unreferenced object can be reclaimed. In a programming language like C, allocating and deallocating memory is a manual process. In Java, process of deallocating memory is handled automatically by the garbage collector.
Have you ever seen an OutOfMemoryError? I'm sure you have. But then, did you understood that line you copied from StackOverflow?
If you haven't, and if you want a gently introduction to the complex world of Java Garbage Collection this is your talk.
I'll talk about garbage collection concepts, the garbage collection in the Hotspot JVM (the default in Oraclel's JDK/JRE) and I'll try to put it in terms that any Java developer can grasp. The next time you'll face the dreaded 'OutOfMemoryError', at least, you'll know what are you up against.
Garbage collection is the most famous (infamous) JVM mechanism and it dates back to Java 1.0. Every Java developer knows about its existence yet most of the time we wish we can ignore its behavior and assume it works perfectly. Unfortunately this is not the case and if you are ignoring it, GC may hit you really hard.... in production. Furthermore the information that you may find on the web can be a lot of times misleading. In this event we will try to demystify some of the misconceptions around GC by understanding how different GC mechanisms work and how to make the right decisions in order to make them work for you.
JVM memory metrics and rules for detecting likely OOM caused crashAjit Bhingarkar
The document describes memory usage pattern in JVM at OOM, and identifies rules for an early detection system which can alert about impending OOM error, and hence a crash.
GARBAGE COLLECTOR Automatic garbage collection is the process of looking at heap memory, identifying which objects are in use and which are not, and deleting the unused objects. An in use object, or a referenced object, means that some part of your program still maintains a pointer to that object. An unused object, or unreferenced object, is no longer referenced by any part of your program. So the memory used by an unreferenced object can be reclaimed. In a programming language like C, allocating and deallocating memory is a manual process. In Java, process of deallocating memory is handled automatically by the garbage collector.
Have you ever seen an OutOfMemoryError? I'm sure you have. But then, did you understood that line you copied from StackOverflow?
If you haven't, and if you want a gently introduction to the complex world of Java Garbage Collection this is your talk.
I'll talk about garbage collection concepts, the garbage collection in the Hotspot JVM (the default in Oraclel's JDK/JRE) and I'll try to put it in terms that any Java developer can grasp. The next time you'll face the dreaded 'OutOfMemoryError', at least, you'll know what are you up against.
Garbage collection is the most famous (infamous) JVM mechanism and it dates back to Java 1.0. Every Java developer knows about its existence yet most of the time we wish we can ignore its behavior and assume it works perfectly. Unfortunately this is not the case and if you are ignoring it, GC may hit you really hard.... in production. Furthermore the information that you may find on the web can be a lot of times misleading. In this event we will try to demystify some of the misconceptions around GC by understanding how different GC mechanisms work and how to make the right decisions in order to make them work for you.
This session is all about - the mechanism provided by Java Virtual Machine to reclaim heap space from objects which are eligible for Garbage collection.
For More information, refer to Java EE 7 performance tuning and optimization book:
The book is published by Packt Publishing:
http://www.packtpub.com/java-ee-7-performance-tuning-and-optimization/book
Virtual machines don't have to be slow, they don't even have to be slower than running native code.
All you have to do is write your code, lay back and let the JVM do its magic !
Learn about various JVM runtime optimizations and why is it considered one of the best VMs in the world.
ExlTech has come up with the Exclusive Java Training course.Hurry and grab the opportunity to become successful Java professional in worlds up growing technologies.
An introduction into the Garbage First (G1) garbage collector for the JVM. The session covers general GC concepts, the fundamentals of G1 and how to setup and tune the JVM for G1.
The Generational Garbage collection involves organizing the heap into different divisions of memory space
in-order to filter long-lived objects from short-lived objects through moving the surviving object of each
generation’s GC cycle to another memory space, updating its age and reclaiming space from the dead
ones. The problem in this method is that, the longer an object is alive during its initial generations, the
longer the garbage collector will have to deal with it by checking for its reachability from the root and
promoting it to other space divisions, where as the ultimate goal of the GC is to reclaim memory from
unreachable objects at a minimal time possible. This paper is a proposal of a method where the lifetime of
every object getting into the heap will be predicted and will be placed in heap accordingly for the garbage
collector to deal more with reclaiming space from dead object and less in promoting the live ones to the
higher level.
A Novel Design of a Parallel Machine Learnt Generational Garbage Collector cseij
The Generational Garbage collection involves organizing the heap into different divisions of memory space
in-order to filter long-lived objects from short-lived objects through moving the surviving object of each
generation’s GC cycle to another memory space, updating its age and reclaiming space from the dead
ones. The problem in this method is that, the longer an object is alive during its initial generations, the
longer the garbage collector will have to deal with it by checking for its reachability from the root and
promoting it to other space divisions, where as the ultimate goal of the GC is to reclaim memory from
unreachable objects at a minimal time possible. This paper is a proposal of a method where the lifetime of
every object getting into the heap will be predicted and will be placed in heap accordingly for the garbage
collector to deal more with reclaiming space from dead object and less in promoting the live ones to the
higher level.
This session is all about - the mechanism provided by Java Virtual Machine to reclaim heap space from objects which are eligible for Garbage collection.
For More information, refer to Java EE 7 performance tuning and optimization book:
The book is published by Packt Publishing:
http://www.packtpub.com/java-ee-7-performance-tuning-and-optimization/book
Virtual machines don't have to be slow, they don't even have to be slower than running native code.
All you have to do is write your code, lay back and let the JVM do its magic !
Learn about various JVM runtime optimizations and why is it considered one of the best VMs in the world.
ExlTech has come up with the Exclusive Java Training course.Hurry and grab the opportunity to become successful Java professional in worlds up growing technologies.
An introduction into the Garbage First (G1) garbage collector for the JVM. The session covers general GC concepts, the fundamentals of G1 and how to setup and tune the JVM for G1.
The Generational Garbage collection involves organizing the heap into different divisions of memory space
in-order to filter long-lived objects from short-lived objects through moving the surviving object of each
generation’s GC cycle to another memory space, updating its age and reclaiming space from the dead
ones. The problem in this method is that, the longer an object is alive during its initial generations, the
longer the garbage collector will have to deal with it by checking for its reachability from the root and
promoting it to other space divisions, where as the ultimate goal of the GC is to reclaim memory from
unreachable objects at a minimal time possible. This paper is a proposal of a method where the lifetime of
every object getting into the heap will be predicted and will be placed in heap accordingly for the garbage
collector to deal more with reclaiming space from dead object and less in promoting the live ones to the
higher level.
A Novel Design of a Parallel Machine Learnt Generational Garbage Collector cseij
The Generational Garbage collection involves organizing the heap into different divisions of memory space
in-order to filter long-lived objects from short-lived objects through moving the surviving object of each
generation’s GC cycle to another memory space, updating its age and reclaiming space from the dead
ones. The problem in this method is that, the longer an object is alive during its initial generations, the
longer the garbage collector will have to deal with it by checking for its reachability from the root and
promoting it to other space divisions, where as the ultimate goal of the GC is to reclaim memory from
unreachable objects at a minimal time possible. This paper is a proposal of a method where the lifetime of
every object getting into the heap will be predicted and will be placed in heap accordingly for the garbage
collector to deal more with reclaiming space from dead object and less in promoting the live ones to the
higher level.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
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Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Fundamentals of Electric Drives and its applications.pptx
JVM memory metrics and rules for detecting possible OOM caused crash
1. Ajit Bhingarkar | a_bhingarkar@yahoo.com
1
JVM memory metrics and rules for detecting OOM caused crash
Why OOM due to memory leaks?
Java objects, because of either design or coding errors, remain live for very long periods of time, contrary to the programmer's intentions. Such objects have been called lingering objects. Lingering objects tend to accumulate over time, clogging the heap and causing multiple performance problems, eventually leading to an application "Out of Memory" problem.
Heap partitions:
.
New space (Eden): New generation heap space for short lived objects marked as NEW space.
Old space: The old generation containing long-lived objects.
Objects are initially allocated into the Eden area. When the Eden area is full, the garbage collector must find the live objects and move them to either the Survivor "To" area or the “Old Space”. The Garbage Collector will strive to keep the newly created objects in the New Space by copying the live objects between the ‘From’ and ‘To’ areas for a certain number of garbage collections. An object ages each time it survives a garbage collection event. It becomes designated as old after surviving a certain number of garbage collection events, at which point it is moved to the old area of the heap.
There are 2 types of GC cycles which happen in a JVM:
A scavenge garbage collection event is one during which only short-lived unused objects are collected in the young generation.
In contrast a full garbage collection involves collection of objects in both the young and old generations.
So there are essentially two GC threads running. One is a very lightweight thread which does "little" collections primarily on the Eden (a.k.a. Young) generation of the heap (scavenge GC). The other is the Full GC thread which traverses the entire heap when there is not enough memory left to allocate space for objects which get promoted from the Eden to the older generation(s).
2. Ajit Bhingarkar | a_bhingarkar@yahoo.com
2
Pattern seen before OOM crash due to memory leaks:
If there is a memory leak or inadequate heap allocated, eventually the older generation will start to run out of room causing the Full GC thread to run (nearly) continuously. Since this process "stops the world" i.e. JVM suspends application execution completely, application is freeze with requests piling up.
Ideally, the GC log should contain many scavenge GCs and few full GCs. However when long living objects fill up the old space of the heap; very few scavenge GC cycles happen and frequent full GC cycle start happening without resulting in any free heap. One of the side effects of the full GC cycle is that all survivors from the young generation are moved to the old generation, which further fills up the old space. Memory leaks are primary cause of this symptom.
Algorithm for alerts:
Normal case: Number of active threads goes up -> memory usage goes up
If memory utilization stays above 60% - check
1. # of active threads or CPU usage
2. Track tenured memory (long lived objects) over a period
3. If old space is above a threshold and # of active threads has not increased
– raise first alarm
– check GC logs to compare scavenge cycle Vs full GC cycle frequency
– if scavenge cycles are below a threshold raise the second alarm
– if full GC cycle frequency exceeds a threshold raise final SOS alarm
Following graph describes the GC cycles just before a crash due to OOM, which also supports the algorithm above.
Note: Code (with a running demo) is available for sharing if requested.