Sun Hotspot 1.4.1
Using a genetic collector, it divides the heap into three main domains: new domain, old domain, and permanent domain.
JVM
All new objects generated are placed in a new domain. Once the object has experienced a certain number of garbage collection cycles, the use period is obtained and enters the old domain. In the permanent domain
JVM
Store
Class
with
Method
Object. In terms of configuration, the permanent domain is a separate domain and is not considered part of the stack. The following describes how to control the size of these domains.
be usable
-XMS
with
-Xmx
Control the original size or maximum of the entire heap. For example, the following command sets the initial size to
128M
:
Java -XMS
128M
-Xmx
256M
To control the size of the new domain, you can use
-Xx: Newratio
Set the proportion of the new domain in the heap. For example, the following command sets the entire heap to
128M
, New domain ratio set
3
That is, the proportion of the new domain and the old domain is
1
:
3
, The new field is a heap
1/4
or
32M
:
Java -XMS
128M
-Xmx
128M
-Xx: newratio = 3
be usable
-Xx: Newsize
with
-Xx: MaxNewsize
Set the initial value and maximum of the new domain. For example, the following command sets the initial value and maximum value of the new domain to
64M
: Java -xms
256M
-Xmx
256M
-Xmn
64M
The permanent domain is generally not part of the pile. Permanent domain default size
4M
. When running the program,
JVM
The size of the permanent domain will be adjusted to meet the needs. Each time you adjust,
JVM
A complete garbage collection will be made to the heap. use
-Xx: maxPersize
Sign to increase the permanent domain. in
WebLogic Server
When the application loads more categories, the maximum value of the permanent domain often needs to be increased. when
JVM
When loading a class, the object in the permanent domain has increased sharply, thus
JVM
Continuously adjust the permanent domain size. To avoid adjustment, you can use
-Xx: Persize
The logo sets the initial value. For example, the permanent domain initial value is set to
32M
And the maximum is set to
64M
.
Java -XMS
512M
-Xmx
512M
-Xmn
128M
-Xx: permsize =
32M
-Xx: maxpermsize =
64M
By default,
Hotspot
Use a replication collector in a new domain. This domain is generally divided into three parts. The first part is
Eden
Used to generate new objects. The other two is called the rescue space, when
Eden
When full, the collector stops the application and copy all the reachable objects to the current
From
Help space, once the current
From
The rescue space is full, the collector copies the reachable object to the current
TO
Help space.
From
with
TO
Help spatial interchange role. Maintaining activities will continue to replicate in the rescue space until they get in use and transfer to the old domain.
use
-Xx: Survivorratio
The size of the new domain subspace can be controlled. with
NEWRATION
same,
Survivorration
Specify a rescue domain and
Eden
The ratio of space. For example, the following command sets the new domain to
64M
,
Eden
Take up
32M
Each rescue domain accounted for
16m
:
Java -XMS
256M
-Xmx
256M
-Xmn
64M
-Xx: survivorration = 2
As mentioned earlier, by default
Hotspot
Use the replication collector for the new domain to use the tag-clear-compressed collector for the old domain. There is a lot of significance to use the replication collector in the new domain because the application is generated - Bidi-Language: Ar-Sa; MSO-ASCII-FONT-FAMILY: 'TIMES New Roman'; MSO-HANSI-FONT- Family: 'Times New Roman'; MSO-BIDI-FONT-FAMILY: 'TIMES New Roman' "> The object of the space is long life, then theoretically moves them into the old domain to avoid repeated replication in the rescue space. However, the application cannot suit this ideal because they have a small part of the longest life. It is best to keep these long life objects and placed in a new domain, because copying small parts of objects total ratio compressed old domain cheap.
To control the copy of the object in the new domain, available
-Xx: Targetsurvivorratio
Control the proportion of rescue space. This value is a percentage, the default value is
50
. When a larger stack is low
Sruvivorratio
When it should be added to
80
to
90
To make better use of rescue space.
use
-Xx: maxtenuring threshold
Controlled upper. All of the replication occurred and hope objects
Eden
Extended to the old domain, you can
Maxtenuring threshold
Set
0
. After the setting is complete, it is actually no longer used the rescue space, so it should be
Survivorratio
Set to maximum to maximize
Eden
Space, set as follows:
Java ... -xx: maxtenuringthreshold = 0 -xx: Survivorratio
=
5000 ...
Here is how to
JVM
Get information in the adjustment scheme.
-verbose.gc
Switch can be displayed
GC
Operation content. Open it, you can display the time that the most busy and the most idle collection behavior occurs, collect the memory size before and after collecting, collecting the time required.
turn on
-xx: printgcdetails
Switch, you can learn more
GC
Changes in.
turn on
-Xx: printgctimestamps
Switch, you can understand the time of these garbage collection,
JVM
Mel then the startup.
Finally, through
-xx: Printheapatgc
Switch understands more detailed information on the heap.
In order to understand the situation in the new field, you can pass
-Xx: = PrinttenUringDistribution
Switch understands the object of the use period.
