Detailed analysis and handling of java cpu soaring problem

Excessive CPU usage in Java is a common problem. There are many reasons and various specific scenarios may be encountered in actual production environments. The following is a detailed analysis of the reasons for the surge in Java CPU and the actual scenarios in production:

Reasons for the surge in Java CPUs

• Too many threads：

  • Each thread of a Java application will occupy a certain amount of CPU resources. When there are too many threads, it will cause excessive CPU usage.
  • Thread context switching can also consume CPU resources. If multiple threads need to be executed, the CPU needs to schedule different threads through context switching, which includes saving the execution status of the running thread and letting the waiting thread resume execution.

• A dead cycle：

  • When there is a dead loop in the program, the CPU will continue to run, resulting in the problem of excessive CPU usage.
  • The dead loop may be caused by program logic errors or data exceptions.

• Long-term blockage：

  • Long-term blocking operations, such as database query, network request, IO operation, etc., will cause the CPU to be unable to fully utilize, resulting in the problem of excessive CPU usage.

• Deadlock：

  • Deadlock refers to two or more threads waiting for each other to release resources, causing the program to be unable to continue execution.
  • When the program enters a deadlock state, the CPU will be occupied, causing the problem of excessive CPU usage.

• GC frequently：

  • If the visits are high, it may lead to frequent GC or even FGC (Full Garbage Collection). When the call volume is large, the memory allocation will be so fast that the GC threads will execute continuously, which will cause the CPU to soar.

• Memory leak：

  • Memory leaks in Java programs will cause the Java virtual machine to continuously allocate memory without releasing it, which will eventually lead to memory overflow, which will lead to a surge in the CPU.

• Serialization and deserialization：

  • When performing serialization and deserialization operations, if the number of calls increases, it may cause CPU usage to increase.

• Regular expressions：

  • The engine implementation used by Java regular expressions is an NFA automaton, which may perform backtracking during character matching, resulting in an increase in CPU usage.

Actual scenarios in production

• High concurrency scenarios：

  • In high concurrency scenarios, Java programs may cause CPU surges due to processing a large number of requests.
  • Especially when there are problems such as dead loops in the program and frequent GC caused by large number of object creation, the CPU usage will further increase.

• Database operations：

  • When performing database query or data modification operations, the system needs to consume a large amount of CPU resources to maintain consistency from the storage system and memory data.
  • If SQL statements perform poorly, for example, fields without indexes are frequently queried, it will cause the CPU to soar.

• Network request：

  • When making network requests, if the number of requests is too large or the request processing time is too long, it will also lead to an increase in CPU usage.

• IO operation：

  • Frequent IO operations, such as file reading and writing, disk access, etc., will also consume a lot of CPU resources.

Solution

In response to the problem of soaring Java CPUs, the following solutions can be adopted:

• Thread pool management：

  • Use thread pools to manage threads and avoid creating too many threads.

• Optimize the dead loop：

  • Check and optimize the dead loop logic in the program to avoid meaninglessly occupying the CPU.

• Asynchronous operation：

  • Change some time-consuming operations to perform asynchronously to reduce CPU usage.

• Optimize resource management：

  • Rationally manage resources such as memory, database connections, and avoid resource leakage and frequent GC.

• JVM parameter tuning：

  • Adjust JVM parameters according to actual conditions, such as heap size, garbage collector, etc., to improve the performance of the JVM.

• Code optimization：

  • Optimize the code to reduce unnecessary calculations and IO operations.

• Use cache：

  • Caching technology is used to reduce the number of database access and network requests, thereby reducing CPU usage.

To sum up, the reasons for the surge in Java CPUs are diverse and complex, and they need to be investigated and optimized according to actual conditions in the production environment. Through reasonable thread management, code optimization, resource management and JVM parameter tuning, CPU usage can be effectively reduced and system performance can be improved.

When there is a memory leak problem in Java programs, it can indeed lead to a series of chain reactions that can eventually trigger a CPU soar. I will explain this process in detail below:

Definition of memory leak

Memory leak refers to the program failing to release the memory in time for some reason (such as logical errors, programming negligence, etc.) after dynamically allocating memory, which makes it impossible for these memory to be reused. Over time, more and more memory leaks will eventually lead to the exhaustion of memory resources.

The impact of memory leaks on Java virtual machines

In Java, memory management is mainly managed by the Java virtual machine (JVM). The JVM automatically recycles memory that is no longer used through a garbage collector (GC). However, when there is a memory leak in the program, the JVM's garbage collector may not be able to recycle these leaked memory, because the program still holds references to these memory (although these references may be unintentional or unnecessary).

The relationship between memory overflow and memory leak

As memory leaks intensify, the available memory in the JVM will gradually decrease. When the available memory is insufficient, the JVM will not be able to satisfy the memory allocation request for the new object, which may cause a memory overflow exception (e.g.). Memory overflow is one of the serious consequences of memory leaks.

The impact of memory overflow on the CPU

Memory overflow not only causes program crashes or behavior abnormalities, but can also have a negative impact on the CPU. Here are some possible scenarios:

• The garbage collector runs frequently: To reclaim as much memory as possible, the garbage collector may run more frequently. This increases the CPU burden, as garbage collection is a compute-intensive task.

• Memory paging and exchange: When physical memory is insufficient, the operating system may swap part of the memory pages to swap space on disk. This can lead to frequent disk IO operations, thereby degrading system performance. At the same time, when the program needs to access these swapped memory pages, a page fault will occur, which will also lead to waste of CPU time.

• Abnormal program behavior: Memory overflow may cause abnormal program behavior, such as infinite loops, deadlocks, etc. These abnormal behaviors will further consume CPU resources.

• System resource competition: In memory tight situations, multiple processes or threads may compete for limited memory resources. This competition may lead to increased context switching, decreased cache hit rate, etc., which further reduces system performance.

Direct and indirect reasons for the CPU soaring

While memory leaks themselves don't directly cause CPU soaring, it can indirectly lead to an increase in CPU usage through a series of aforementioned chain reactions. Direct causes may include frequent operation of the garbage collector, increased disk IO operations caused by memory paging and exchange, abnormal program behavior, and competition for system resources.

Solution

To resolve memory leaks and avoid CPU soaring, the following measures can be taken:

• Use memory analysis tools (such as VisualVM, JProfiler, etc.) to detect memory leaks.
• Optimize the code to ensure that memory that is no longer used is released in time.
• Adjust JVM parameters, such as heap size, garbage collection strategy, etc. to meet the memory needs of the program.
• Monitor the system's memory and CPU usage, and discover and solve problems in a timely manner.

To sum up, although memory leaks themselves will not directly cause CPU soaring, it can indirectly affect CPU performance through a series of chain reactions. Therefore, when developing Java programs, special attention should be paid to memory management issues to avoid memory leaks and related performance issues.

Before explaining why long-term blocking operations can cause CPU to be inadequate, resulting in excessive CPU usage, we need to understand several key concepts: blocking operations, CPU utilization, and concurrent/parallel processing.

Blocking operation

A blocking operation refers to operations that will pause further execution of the program during execution until the operation is completed or some conditions are met. This type of operation usually involves waiting for external resources or events, such as database queries, network requests, file read and write (IO operations), etc. During these operations, the program "blocks" or "hangs" until the operation is completed, and no other tasks are performed during this time.

CPU Utilization

CPU utilization is a measure of the proportion of CPUs being busy processing tasks over a period of time. Ideally, we want the CPU to stay busy, but at the same time we should avoid over-awaiting external resources, as this will lead to waste of CPU resources.

Concurrent/parallel processing

Concurrency and parallel processing are key technologies to improve program efficiency and CPU utilization. Concurrency allows a program to process multiple tasks simultaneously, even if these tasks may not be executed simultaneously (for example, multitasking is achieved through time slice rotation). Parallel means that multiple tasks are executed simultaneously, which usually depends on multi-core or multi-processor systems.

The impact of long-term blocking operations

When a program performs a long blocking operation, the following situations occur:

• CPU idle: Since blocking operations require waiting for external resources (such as database responses, network data arrival, etc.), the CPU cannot perform other tasks during this period, resulting in idle CPU resources.

• Thread/process hangs: If the blocking operation is performed at the thread or process level, the entire thread or process will hang and other tasks cannot be continued. In a multi-threaded or multi-process environment, this will cause other runnable threads or processes to not be scheduled in time, further reducing CPU utilization.

• Context Switching Overhead: If the system tries to run other tasks through context switch to utilize CPU resources, frequent context switches themselves will also consume CPU resources, reducing overall performance.

• System response slow: Because CPU resources are occupied by blocked operations (or indirectly causing other tasks to be unable to be executed in time), the overall system response speed may slow down and the user experience will decline.

Solution

To solve the CPU utilization problem caused by long-term blocking operations, the following strategies can be adopted:

• Asynchronous processing: Use asynchronous programming models, such as callback functions, Promise, async/await, etc., to allow the program to continue to perform other tasks while waiting for external resources.

• Multithreaded/multiprocess: For IO-intensive tasks, multiple threads or multiple processes can be used to process multiple tasks in parallel, reducing the time when a single task blocks the CPU.

• Event-driven programming: Through the event-driven model, programs can respond when events occur, rather than actively waiting for events to complete, thereby improving CPU utilization.

• Optimize external resource access: For example, optimizing database queries, using cache to reduce network requests, etc. can reduce the time of blocking operations.

To sum up, long-term blocking operations will lead to inadequate use of CPU resources, resulting in the problem of excessive CPU usage. By adopting strategies such as asynchronous processing, multi-threading/multi-process, event-driven programming and optimizing external resource access, this problem can be effectively alleviated and the performance and user experience of the program can be improved.

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