Shulou(Shulou.com)06/03 Report--

1. Memory leak:

The memory leak of Java means that some objects are no longer used by the application, but the garbage collector (Garbage Collector) does not recognize them as "no longer used", so these objects are not reclaimed, or for some reason they cannot be recycled or are not completely recycled!

For example:

Various connections, such as database connections (dataSourse.getConnection ()), network connections (socket), and io connections, are not automatically reclaimed by GC unless they explicitly call their close () method to close their connections.

The static collection class is not released-the object is not released

There are too many levels of recursive calls

If those objects that are not in use take up enough space on the heap (heap) that the application cannot meet the next memory allocation requirements, it will result in an OutOfMemoryError error.

There is a difference between a memory leak and a system overload, although the end result may be the same.

A memory leak is an error caused by the non-recovery of used resources, while the system is overloaded because the system really does not have that many resources to allocate (other resources are in use).

Memory leaks can be solved by software tuning, while system overload can only be solved by updating hardware.

two。 Performance of memory leaks

-memory is almost full, but not yet full, at a critical point, there will be no errors, but it will affect performance

-OOM and other errors are clearly generated in the log. For example, in the following figure, the basic level of landing points indicates normal recycling, while the recovery is not complete.

3. Troubleshooting ideas for memory leaks:

-key parameter settings for JVM and GC (for example, if-Xms-Xmx is not set, memory leaks may occur)

-troubleshooting code

Common types of 4.OutOfMemory

-heap space is full: https://blog.51cto.com/11009785/2382260

-permanent generation / meta space is full: https://blog.51cto.com/11009785/2379670

-Stack overflow: java.lang.stackoverflowerror;fatal:stack size too small

Troubleshooting: first look at the parameter-Xss: the stack size of each thread, which is used to save function calls, return addresses, etc., the default is 1m, if an error is reported, it will be changed to 2m, if not, take a snapshot and check the code. There may be too many layers of recursive calls.

-system memory is full: java.lang.outofmemoryerror:unable to create new native thread

Solution: upgrade hardware

Possible causes of 5.java.lang.OutOfMemoryError errors and troubleshooting ideas:

-insufficient space

-first of all, check if it is a hardware problem.

-if the hardware is good, check the parameters again, whether the setting is too small

-memory leak

-if there is nothing wrong with the hardware and parameters, it is suspected that it is a memory leak. You need to check the parameter settings of JVM and GC. If not, you need to check the code.

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