garbage collector run

Chapter 5 JVM garbage collector (1): jvm garbage collection (The garbage collection algorithm is a theory, and the garbage collector is a collection algorithm. For details about the collection algorithm, see Chapter 4 JVM

Bibliography: In-depth understanding of Java Virtual Machine Zhou ZhimingJava Programming Ideas Bruce EckelWhy do we need to know about GC after automated garbage collection: When we need to troubleshoot various overflow, memory leak issues, when garbage collections become a bottleneck for the system to reach a higher concurrency, we have to implement the necessary monitoring and tuning of these "automated"

Serial Oldcollectors areJAVAone of the garbage collectors in a virtual machine,itis aSerialThe old-age version of the collector, which is also a single-threaded collector, uses the "tag-collation "algorithm. This collector is also mainly in the currentJAVAof theClientvirtual machines in the mode of use. If theServermod

sensitive to CPU resources. Cause: Programs that are designed for concurrency are more sensitive to CPU resources. When concurrency occurs, because the application slows down by taking up a portion of the thread (or CPU resources), the overall throughput decreases, the application slows, and is especially noticeable when the number of CPUs is low.Workaround: Incremental concurrency Collector (I-CMS): Allows GC threads to

1. Serial Collector The serial collector is a single thread collector, but its "single-threaded" meaning does not simply mean that it uses only one CPU or a collection thread to do the garbage collection, and more importantly, when it does garbage collection, all the other w

　　Based on the "in-depth understanding of Java Virtual Machines", this book summarizes　　I. About several concepts: (tag garbage algorithm, garbage collection algorithm, garbage collector)There are two ways to find JVM garbage: The reference counting method/accessibility algo

Parallel scavenge collector is also a new generation collector, and it is also a collector with a replication algorithm and a parallel multithreaded collector. The feature of the parallel scavenge collector is that its focus is different from that of other collectors, and t

If the collection algorithm is the method of memory recycling, then the garbage collector is the specific implementation of memory recycling. In the Java Virtual Machine specification, how the object garbage collector should be implemented does not have any rules, so different vendors, different versions of the virtual

user threads; The old age uses the tag-collation algorithm and pauses all user threads. Parallel Scavenge The Parallel scavenge collector is also very similar to the parnew algorithm, but most of the concerns with other collectors are to minimize the downtime of the user thread when garbage collection occurs, while the Parallel scavenge collector is designed t

Garbage collector and Memory allocation policy (ii)--garbage collection algorithm JAVAJVM garbage collectorSimple understanding of the idea of algorithms1. Mark-Sweep algorithmMark-sweep algorithm is divided into two stages: Mark and clear the objects that need to be recycled (see the accessibility analysis in the prev

Chapter 6 JVM garbage collector (2) jvm garbage collection The previous chapter records several common garbage collectors. For details, see chapter 5 JVM garbage collector (1). 1. G1 Note: From the Perspective, compared with C

that are accessible from the root node, then move all objects to one end, and then clear out the memory benefits beyond the bounds: no memory fragmentation Disadvantage: The object is moved on top of the tag, the cost is relatively high, The efficiency is also not high 4. Generational recovery algorithm 2. The new generation of collector serial single-threaded: simple and efficient parnew serial multi-threaded version, with the CMS, can not be combin

existence in program code, similar to Object obj = new object () such a reference, as long as a strong reference exists, the garbage collector is never recyclable objects.Soft references: is used to describe some objects that are also useful but not necessary. For objects associated with soft references, this type of object will be recycled two times before a memory overflow exception occurs in the system.

the following garbage collection processors:AThe figure above shows the garbage collector graph in jdk1.7. The two are connected to indicate that they can be used in combination. The Recycler also applies to the young and old generations because the available regions are divided into the young and old generations. In addition, there are no advantages or disadvan

, the initial mark (Initial Mark), the concurrency tag (Concurrent mark), the remark, and concurrent Cleanup (Concurrent Sweep). Note that there is no merge operation, so there will be fragmentation. Initialization phase: Pauses the application thread, finds all surviving objects, takes a short time, and the collector uses a single thread. Concurrent Tag phase: The Collector tag operation and the

Introduction to V8 garbage collection mechanismThe implementation of the V8 garbage collector is a very important reason for V8 efficiency.V8 automatically reclaims object memory that is no longer needed at run time, which is also garbage collection.V8 uses a combination of

recycled (x in the figure). At the same time, the object activity of each region (the proportion of the surviving objects in the region) is calculated during the concurrent tagging process.4, Remark, re-mark, there will be a short pause (STW). The re-tagging phase is used to collect the concurrency tag phase to generate new garbage (concurrent phases and applications run together), and the G1 uses a faster

when the parallel collector is collected. The number of parallel collection threads.-xx:maxgcpausemillis=n: Set maximum pause time for parallel collection-xx:gctimeratio=n: Sets the percentage of time that garbage collection takes to run the program. The formula is 1/(1+n)Concurrent collector Settings-xx:+cmsincrement

the objects in these areas are selected as GC roots, and the objects referenced by GC roots are not recycled by GC.　　　　If you want to refine GC ROOTS,GC Roots include:　　　　　　1, all aged with objects2, all global objects3, all JNI handles4, all Locked objectsObjects held by 5,JVMTI6, Code snippet Code_cache7, all ClassLoader, and its loaded class8, all dictionaries9,flat_profiler and Management10, most importantly, all of the reference type variables running on the thread stack. 3. Referring to e

each old generation garbage collection cycle, the concurrent collector at the beginning of the collection will briefly pause the entire application, pausing again in the collection. The second pause is slightly longer than the first, and multiple threads are garbage collected at the same time during this process. 2. The concurrency