Databases Reference
In-Depth Information
•
Max
: This ield shows the maximum memory that can be used for
memory management.
•
GC Time
: This ield shows the total GC time spent by the garbage collector.
It shows the time for which other threads were stopped to perform GC.
During monitoring, if we ind that the Survivor space is full most of the time,
it indicates the size of the young generation (Eden plus Survivor space) is not
enough. Because of that it will move more objects into the old generation space.
This will increase the possibility of a major GC. Hence, the young generation size
should be tuned. The following JVM parameters help in the coniguration of the
young generation:
•
NewRatio
: This parameter controls the size of the young generation. If
the value of this parameter is four, the size of the young generation space
(Eden plus Survivor) will be one fourth of the total heap. The rest of the
space will be used by the Tenured space.
•
NewSize
: This parameter deines the minimum size of the young
generation space.
•
MaxNewSize
: This parameter deines the upper limit of the young
generation size.
•
SurvivorRatio
: This parameter deines the ratio of the Survivor and Eden
space. If it is conigured to six, the Survivor space will be one sixth of the
total young generation space.
During a load test, if the trend of the heap memory chart is going upward throughout
the load test, it indicates the possibility of a memory leak in the application. In order
to conclude this we should run the load test for a longer duration.
During the load test, if it is found that garbage collection is happening again and
again, the heap size needs to be tuned. It may be because the young generation is
not conigured properly or the total heap size is not conigured correctly.
During the load test, if it is found that the Permanent generation size is reaching
near the maximum Permanent generation size, it is recommended to increase the
Permanent generation space.
JVM tuning in itself is a vast topic. We learned a few of the
important JVM tuning options. For more information about
garbage collection tuning, please refer to the following URL:
http://www.kgs.ku.edu/Publications/ancient/f15_
snails.html
