JNI Rendering Memory Limits
===========================
JMuPdf uses native libraries, i.e, DLL's or SO's. These libraries use memory at the OS
level. This means that this memory isn't controlled by the JVM.
JMuPdf provides a mechanism to control the maximum amount of memory that is allocated on
a per document basis. The default maximum memory used per document is 60mb. This can be
changed at runtime when creating a new document object.
example PDF:
int maxMemory = 20;
PdfDocument pdf = new PdfDocument("c:\\test.pdf", maxMemory);
example XPS:
int maxMemory = 20;
XpsDocument xps = new XpsDocument("c:\\test.pdf", maxMemory);
The examples above will set the max memory to be used to 20mb. Once a document is closed the memory is freed.
Additional memory considerations should be taken when rendering multiple documents simultaneously. Each document
can have its own memory limit but the total memory used will be the sum of the memory limits used for each
document. For example:
int maxMemory = 20;
PdfDocument pdf1 = new PdfDocument("c:\\test.pdf", maxMemory);
PdfDocument pdf2 = new PdfDocument("c:\\test.pdf", maxMemory);
In this case JMuPDF may use upto 40mb while rendering.
int maxMemory = 20;
PdfDocument pdf1 = new PdfDocument("c:\\test.pdf", maxMemory);
maxMemory = 10;
PdfDocument pdf2 = new PdfDocument("c:\\test.pdf", maxMemory);
In this case JMuPdf could use upto 30mb of memory while rendering.
JVM Memory
==========
As JAVA starts, it creates within the systems memory a Java Virtual Machine (JVM).
JVM is where the complete processing of any Java program takes place. All JAVA
applications by default allocates & reserves up to 64 MB of memory resource pool
from the system on which it is running.
-Xms
====
The Xms is the initial / minimum Java memory (heap) size within the JVM. Setting the initial
memory (heap) size higher can help in a couple of ways. First, it will allow garbage collection
(GC) to work less which is more efficient. The higher initial memory value will cause the size
of the memory (heap) not to have to grow as fast as a lower initial memory (heap) size, thereby
saving the overhead of the Java VM asking the OS for more memory.
-Xmx
====
The Xmx is the maximum Java memory (heap) size within the Java Virtual Memory (JVM). As the JVM
gets closer to fully utilizing the initial memory, it checks the Xmx settings to find out if it
can draw more memory from the system resources. If it can, it does so. For the JVM to allocate contiguous
memory to itself is a very expensive operation. So as the JVM gets closer to the initial memory, the
JVM will use aggressive garbage collection (to clean the memory and if possible avoid memory allocation),
increasing the load on the system.
-XX:PermSize
============
The section of the heap reserved for the permanent generation holds all of the reflective data for the JVM.
This size should be increased to optimize the performance of applications that dynamically load and unload
a lot of classes. Setting this to a value of 128MB eliminates the overhead of increasing this part of the heap.
-XX:MaxPermSize
===============
-XX:MaxPermSize=64m Size of the Permanent Generation.
[5.0 and newer: 64 bit VMs are scaled 30% larger; 1.4 amd64: 96m; 1.3.1 -client: 32m.]
Example settings
================
-Xms1g
-Xmx2g
-XX:PermSize=512m
-XX:MaxPermSize=512m