Use of the jstat of the JDK

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The use of Jstat

To determine if the JVM has memory problems? How can I tell if the JVM garbage collection is normal? The general top instruction basically does not satisfy this requirement, because it mainly monitors the overall system resources, it is difficult to locate the Java application.

Jstat is a lightweight gadget that comes with the JDK. The full name "Java Virtual machine Statistics monitoring Tool", which is located in the Java Bin directory, mainly uses the JVM built-in instructions for Java application resources and performance of real-time command line monitoring, including the heap Monitoring of size and garbage collection status. Visible, Jstat is a lightweight, JVM-specific tool that works well. The percentage change in the graph is less noticeable due to the large JVM memory settings

A very strong monitoring VM memory tool. can be used to monitor the size of various heap and non-heap sizes and their memory usage within VM memory.

The Jstat tool is particularly powerful and has a number of options to view in detail the usage of each part of the heap, as well as the number of loaded classes. When used, add the process ID of the viewing process and the selected parameters.

Execution: cd $JAVA _home/bin in the execution of Jstat, note that after Jstat must be followed by parameters.

Syntax structure:

Usage:jstat-help|-options

Jstat-<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]

Parameter explanation:

options-option, we generally use-gcutil to view GC conditions

The VMID-VM process number, which is the currently running Java process number

interval– interval time, in seconds or milliseconds

count-printing times, if the default is printed countless times

Percentage of space used in Survivor space zone 0 on S0-heap
Percentage of space used in Survivor space Zone 1 on S1-heap
Percentage of space used in Eden space on E-heap
The percentage of space used in the old area on the O-heap
Percentage of space already used in the P-perm space area
ygc-number of young GC occurrences from application boot to sample
ygct– the time (in seconds) used by the young GC when booting from the application to sampling
fgc-the number of full GC occurrences from application startup to sampling
fgct– time (in seconds) for full GC from application boot to sampling
gct-total time (in seconds) for garbage collection from application startup to sampling

Instance using 1:

[Email protected] bin]# Jstat-gcutil 25444

S0 S1 E O P ygc ygct FGC fgct GCT

11.63 0.00 56.46 66.92 98.49 162 0.248 6 0.331 0.579

Instance using 2: (25444 is the Java process number, PS-EF | grep java)

[Email protected] bin]# Jstat-gcutil 25444 1000 5

S0 S1 E O P ygc ygct FGC fgct GCT

73.54 0.00 99.04 67.52 98.49 166 0.252 6 0.331 0.583

73.54 0.00 99.04 67.52 98.49 166 0.252 6 0.331 0.583

73.54 0.00 99.04 67.52 98.49 166 0.252 6 0.331 0.583

73.54 0.00 99.04 67.52 98.49 166 0.252 6 0.331 0.583

73.54 0.00 99.04 67.52 98.49 166 0.252 6 0.331 0.583

As we can see, 5 times after the young GC, the garbage memory was put into the old space (O) from the Eden Space (E) and caused a change in percentage, causing the percentage of survivor space to be reduced from 73.54% (S0) to 0% (S1). Effectively frees up memory space. Green box, we can see that after a full GC, the memory of the old Space Area (O) is recycled from 99.05% to 67.52%.

The total number of times for both the young GC and the full GC is printed at the same time. And, each time that the young GC consumes, it can be subtracted from two lines of YGCT in the phase interval. Each time the full GC is consumed, it can be subtracted from two lines fgct apart. For example, the first row represented in the red box and the second row occurred 1 times with the young GC, which consumed a time of 0.252-0.252=0.0 seconds.

Resident Memory Area (P) usage, always stay around 98.49%, indicating that resident memory does not mutate, more normal.

If both the young GC and the full GC can occur properly, and both can effectively reclaim memory, the resident memory area is not significantly changed, then the Java memory release is normal, garbage collection is timely, the chance of Java memory leakage will be greatly reduced. But it does not necessarily indicate that there is no memory leak.

GCT is the sum of time for YGCT and FGCT.

Above, this article describes the function of Jstat to view GC status by percentage. In fact, it also has functions, such as load class information statistics function, memory pool information statistics function, those are in the form of absolute value printed out, less use, do not introduce here.

[Email protected] bin]# Ps-ef | grep java

Root 25917 1 2 23:23 pts/2 00:00:05/usr/local/jdk1.5/bin/java-djava.endorsed.dirs=/usr/local/jakarta-tomcat- 5.0.30/common/endorsed-classpath/usr/local/jdk1.5/lib/tools.jar:/usr/local/jakarta-tomcat-5.0.30/bin/ bootstrap.jar:/usr/local/jakarta-tomcat-5.0.30/bin/commons-logging-api.jar-dcatalina.base=/usr/local/ jakarta-tomcat-5.0.30-dcatalina.home=/usr/local/jakarta-tomcat-5.0.30-djava.io.tmpdir=/usr/local/ Jakarta-tomcat-5.0.30/temp org.apache.catalina.startup.Bootstrap Start

Jstat-class PID: Displays the number of loaded classes, and the amount of space that is occupied.

Instance using 3:

[Email protected] bin]# Jstat-class 25917

Loaded Bytes Unloaded Bytes time

2629 2916.8 29) 24.6 0.90

Jstat-compiler PID: Displays information such as the number of real-time VMS compiled.

Instance using 4:

[Email protected] bin]# Jstat-compiler 25917

Compiled Failed Invalid Time Failedtype Failedmethod

768 0 0) 0.70 0

Jstat–gccapacity: It can be shown that the use and occupancy of three generation (Young,old,perm) objects in VM memory, such as: PGCMN shows the minimum perm memory usage, PGCMX shows the maximum amount of memory used for Perm, The PGC is the current newly generated perm memory footprint, and the PC is but the pre-perm memory footprint. The other can be based on this analogy, OC is the old inside the pure consumption.

[Email protected] bin]# jstat-gccapacity 25917

NGCMN 640.0

NGCMX 4992.0

NGC 832.0

s0c 64.0

S1c 64.0

EC 704.0

OGCMN 1408.0

OGCMX 60544.0

OGC 9504.0

OC 9504.0 OC is pure consumption in old

PGCMN 8192.0 PGCMN shows the minimum perm memory usage

PGCMX 65536.0 PGCMX shows the maximum amount of memory used for Perm

PGC 12800.0 PGC is the current newly generated perm memory footprint

PC 12800.0 pc Yes but front perm memory consumption

YGC 164

FGC 6

Jstat-gcnew Information for Pid:new objects

[Email protected] bin]# jstat-gcnew 25917

s0c s1c s0u s1u TT MTT DSS EC EU YGC YGCT

64.0 64.0 47.4 0.0 2 15 32.0 704.0 145.7 168 0.254

Jstat-gcnewcapacity information of Pid:new objects and their consumption

[Email protected] bin]# jstat-gcnewcapacity 25917

NGCMN ngcmx NGC s0cmx s0c s1cmx s1c ecmx EC YGC FGC

640.0 4992.0 832.0 64.0 448.0 448.0 64.0 4096.0 704.0 168 6

Jstat-gcold the information for the Pid:old object.

[Email protected] bin]# Jstat-gcold 25917

PC PU OC OU ygc FGC fgct GCT

12800.0 12617.6 9504.0 6561.3 169 6 0.335 0.591

Jstat-gcoldcapacity the information of the Pid:old object and its consumption.

[Email protected] bin]# jstat-gcoldcapacity 25917

OGCMN ogcmx OGC OC ygc FGC fgct GCT

1408.0 60544.0 9504.0 9504.0 169 6 0.335 0.591

Jstat-gcpermcapacity the information of the Pid:perm object and its consumption.

[Email protected] bin]# jstat-gcpermcapacity 25917

PGCMN pgcmx PGC PC ygc FGC fgct GCT

8192.0 65536.0 12800.0 12800.0 169 6 0.335 0.591

Jstat-printcompilation PID: Information for the current VM execution.

[Email protected] bin]# JSTAT-PRINTCOMPILATION-H3 25917 1000 5

Print every 1000 milliseconds, print 5 times, and add-h3 every three lines to show the title.

Compiled Size Type Method

788 1 Java/io/file <init>

788 1 Java/io/file <init>

788 1 Java/io/file <init>

Compiled Size Type Method

788 1 Java/io/file <init>

788 1 Java/io/file <init>

Use of the jstat of the JDK