JVM performance tuning and tools (4)

1: Basic usage of JVM parameters and common tuning methods

        JVM parameters are options for configuring the Java virtual machine, which can tune the behavior and performance of the JVM. The following are the basic usage of JVM parameters and some common tuning methods:

1. Basic usage:

   • Parameter format: JVM parameters start with "-XX:", followed by the parameter name and parameter value. For example: "-XX:MaxHeapSize=512m".
   • Parameter classification: JVM parameters can be divided into standard parameters (starting with -X), non-standard parameters (starting with -XX) and user-defined parameters.

2. Common tuning methods:

   • Heap memory settings: meet the needs of the application by adjusting the size of the heap memory. You can use the "-Xms" parameter to set the initial heap size and the "-Xmx" parameter to set the maximum heap size.
   • Garbage collector selection: select the appropriate garbage collector according to the characteristics and needs of the application, and set the corresponding garbage collector parameters. For example, use "-XX:+UseParallelGC" to enable the parallel collector and "-XX:+UseG1GC" to enable the G1 collector.
   • Parallel thread number setting: Improve the efficiency of garbage collection by adjusting the number of threads of the parallel garbage collector. You can use the "-XX:ParallelGCThreads" parameter to set the number of parallel threads.
   • Garbage collection statistics: Use the "-XX:+PrintGCDetails" and "-XX:+PrintGCDateStamps" parameters to print detailed garbage collection information and timestamps for analysis and tuning.
   • Thread stack size setting: Avoid StackOverflowError exceptions by adjusting the thread stack size. The thread stack size can be set using the "-Xss" parameter.
   • Class loading optimization: use the "-XX:+OptimizeStringConcat" parameter to enable string concatenation optimization, use the "-XX:+UseFastAccessorMethods" parameter to enable fast accessor method optimization, etc.
   • Compiler optimization: Improve code execution performance by adjusting compiler parameters. For example, use the "-XX:+TieredCompilation" parameter to enable tiered compilation optimization, and use the "-XX:CompileThreshold" parameter to set the compilation trigger threshold.

        These are commonly used JVM tuning methods, and other JVM parameters and tuning techniques can also be used for optimization according to the needs and environment of specific applications. When tuning the JVM, it is recommended to conduct testing and performance analysis, gradually adjust parameters according to the actual situation, and monitor the performance indicators of the application to find the best configuration.

2: Tuning and configuration methods for different garbage collectors

1. Serial Collector:

   • Tuning method: The serial collector is single-threaded and is mainly used in simple test environments or small applications. In general, no additional tuning is required.

2. Parallel Collector:

   • Tuning method: The parallel collector uses multiple threads to perform garbage collection tasks in parallel, and performance can be optimized by adjusting the following parameters:
     • "-XX:ParallelGCThreads": Set the number of threads of the parallel garbage collector, usually the same as or slightly more than the number of CPU cores.
     • "-XX:MaxGCPauseMillis": Set the target value of the maximum garbage collection pause time, which can balance throughput and pause time.
     • "-XX:GCTimeRatio": Sets the ratio of garbage collection time to application execution time, used to tune throughput.

3. Concurrent collector (CMS Collector):

   • Tuning method: The Concurrent Mark Sweep Collector (CMS) is a low pause time collector that can be optimized for performance through the following parameters:
     • "-XX:ConcGCThreads": Set the number of threads used in the concurrent marking phase.
     • "-XX:+UseCMSInitiatingOccupancyOnly": Only start CMS collection when the specified threshold is reached, avoiding frequent triggers.
     • "-XX:CMSInitiatingOccupancyFraction": Set the threshold for triggering CMS collection as a percentage of the entire heap.

4. G1 Collector (G1 Collector):

   • Tuning method: The G1 collector is a garbage collector for server applications, and performance can be optimized through the following parameters:
     • "-XX:MaxGCPauseMillis": Sets the target value for the maximum garbage collection pause time.
     • "-XX:G1HeapRegionSize": Set the region size of the G1 collector, affecting throughput and pause time.
     • "-XX:G1NewSizePercent" and "-XX:G1MaxNewSizePercent": Adjust the percentage of the new generation size to the entire heap.

        Regardless of the garbage collector used, tuning should be tested and evaluated based on the specific application and environment. The behavior of the garbage collector can be monitored and tuned by printing garbage collection logs (using the "-XX:+PrintGCDetails" parameter) and performance analysis tools. At the same time, reasonably set the heap memory size and the parameters of the garbage collector to balance throughput, pause time and memory utilization.

3: Optimization techniques and methods of memory allocation strategy

        Optimization tips and methods for memory allocation strategies can help improve application performance and memory utilization. Here are some common optimization techniques and methods:

1. Object reuse: Reuse objects to avoid frequent creation and destruction of objects. Object pools or caches can be used to manage and reuse objects, reducing the overhead of memory allocation.

2. Local variables first: Define temporary variables and object references as local variables, not as member variables. Local variables are automatically released after the method is executed, and will not occupy memory for a long time.

3. Avoid excessive boxing and unboxing: Try to use basic data types instead of wrapper classes, avoid frequent automatic boxing and unboxing operations, and reduce object creation and destruction.

4. String concatenation optimization: When a large number of string concatenations are required, use StringBuilder or StringBuffer to construct strings, avoid frequent string splicing operations, and improve performance.

5. Optimize the initial size of the collection: When creating a collection object, try to specify its initial size to avoid additional memory allocation during the automatic expansion of the collection.

6. Cache data: For frequently used data, it can be cached in memory to avoid repeated calculation or query operations and improve access speed.

7. Use an appropriate data structure: Choosing an appropriate data structure can reduce memory consumption. For example, use array instead of ArrayList, use HashSet instead of ArrayList, etc., and choose the most suitable data structure according to the specific application scenario.

8. Monitoring and tuning: Use performance analysis tools and memory analysis tools to monitor the memory usage of applications, identify memory bottlenecks and optimization points, and perform targeted tuning and optimization.

        The above are some common optimization techniques and methods of memory allocation strategies, which can be adjusted and optimized according to specific application scenarios and requirements. At the same time, performance testing and performance evaluation are the key points in the optimization process to ensure the optimization effect and stability.

4: Commonly used JVM monitoring and diagnostic tools

The following are some commonly used JVM monitoring and diagnostic tools and their simple use introduction:

1. JDK comes with tools:

   • jps: input on the command line jps, all Java processes and their corresponding process IDs in the current system can be displayed.
   • jstat: input on the command line jstat -options <pid> <interval> <count>, you can monitor the heap, class loading, garbage collection and other information of the JVM. For example, jstat -gcutil <pid> 1000 10GC statistics can be sampled 10 times per second.
   • jmap: Entered on the command line jmap -options <pid>, you can generate a heap dump snapshot (Heap Dump) and view the detailed information of the objects in the heap. For example, jmap -dump:format=b,file=heapdump.bin <pid>a heap dump file can be generated.
   • jstack: Entered on the command line jstack <pid>, you can generate a thread dump snapshot (Thread Dump), which is used to view the thread status, call stack and other information.
   • jcmd: Entered on the command line jcmd <pid> <command>, you can send diagnostic commands to the running Java process. For example, jcmd <pid> VM.system_propertiesyou can view system properties.

2. VisualVM: After starting VisualVM, you can monitor and diagnose running Java applications on its interface. It provides real-time monitoring and analysis of CPU, memory, thread and other resources, and supports plug-in extensions. The remote or local Java process to be monitored can be added through "File -> Add JMX Connection".

3. JConsole: Enter on the command line jconsoleto start the JConsole tool. It provides monitoring and management functions for running Java applications. You can select the Java process to be monitored, and then view information such as CPU, memory, and threads.

4. Java Mission Control (JMC): After starting Java Mission Control, you can connect to the running Java process through "File -> Connect". JMC provides real-time monitoring and analysis functions for JVM running status, garbage collection, threads, etc. Various plugins and features of JMC can be used to analyze application performance issues.

5. VisualGC: After installing the VisualGC plug-in in VisualVM, you can view the behavior of the garbage collector and the usage of heap memory under the "Monitor" tab. It visualizes the heap structure, object distribution, garbage collection behavior and other information.

        These tools provide different monitoring and diagnostic functions, through which they can obtain various information of the JVM, identify performance bottlenecks, and perform performance analysis and tuning. When using these tools, you can choose the appropriate tool according to your specific needs, and refer to their documentation and user guide for more detailed usage methods and functions.