What is ‘PermSize’ in Java?
«The permanent generation is used to hold reflective data of the VM itself such as class objects and method objects. These reflective objects are allocated directly into the permanent generation, and it is sized independently from the other generations.» [ref]
In other words, this is where class definitions go (and this explains why you may get the message OutOfMemoryError: PermGen space if an application loads a large number of classes and/or on redeployment).
Note that PermSize is additional to the -Xmx value set by the user on the JVM options. But MaxPermSize allows for the JVM to be able to grow the PermSize to the amount specified. Initially when the VM is loaded, the MaxPermSize will still be the default value (32mb for -client and 64mb for -server ) but will not actually take up that amount until it is needed. On the other hand, if you were to set BOTH PermSize and MaxPermSize to 256mb, you would notice that the overall heap has increased by 256mb additional to the -Xmx setting.
Solution 2
This blog post gives a nice explanation and some background. Basically, the «permanent generation» (whose size is given by PermSize) is used to store things that the JVM has to allocate space for, but which will not (normally) be garbage-collected (hence «permanent») (+). That means for example loaded classes and static fields.
There is also a FAQ on garbage collection directly from Sun, which answers some questions about the permanent generation. Finally, here’s a blog post with a lot of technical detail.
(+) Actually parts of the permanent generation will be GCed, e.g. class objects will be removed when a class is unloaded. But that was uncommon when the permanent generation was introduced into the JVM, hence the name.
Solution 3
The permament pool contains everything that is not your application data, but rather things required for the VM: typically it contains interned strings, the byte code of defined classes, but also other «not yours» pieces of data.
What is ‘PermSize’ in Java?
«The permanent generation is used to hold reflective data of the VM itself such as class objects and method objects. These reflective objects are allocated directly into the permanent generation, and it is sized independently from the other generations.» [ref]
In other words, this is where class definitions go (and this explains why you may get the message OutOfMemoryError: PermGen space if an application loads a large number of classes and/or on redeployment).
Note that PermSize is additional to the -Xmx value set by the user on the JVM options. But MaxPermSize allows for the JVM to be able to grow the PermSize to the amount specified. Initially when the VM is loaded, the MaxPermSize will still be the default value (32mb for -client and 64mb for -server ) but will not actually take up that amount until it is needed. On the other hand, if you were to set BOTH PermSize and MaxPermSize to 256mb, you would notice that the overall heap has increased by 256mb additional to the -Xmx setting.
Solution 2:
This blog post gives a nice explanation and some background. Basically, the «permanent generation» (whose size is given by PermSize) is used to store things that the JVM has to allocate space for, but which will not (normally) be garbage-collected (hence «permanent») (+). That means for example loaded classes and static fields.
There is also a FAQ on garbage collection directly from Sun, which answers some questions about the permanent generation. Finally, here’s a blog post with a lot of technical detail.
(+) Actually parts of the permanent generation will be GCed, e.g. class objects will be removed when a class is unloaded. But that was uncommon when the permanent generation was introduced into the JVM, hence the name.
Solution 3:
The permament pool contains everything that is not your application data, but rather things required for the VM: typically it contains interned strings, the byte code of defined classes, but also other «not yours» pieces of data.
Permgen vs Metaspace in Java
The Kubernetes ecosystem is huge and quite complex, so it’s easy to forget about costs when trying out all of the exciting tools.
To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.
Connect your cluster and start monitoring your K8s costs right away:
We rely on other people’s code in our own work. Every day.
It might be the language you’re writing in, the framework you’re building on, or some esoteric piece of software that does one thing so well you never found the need to implement it yourself.
The problem is, of course, when things fall apart in production — debugging the implementation of a 3rd party library you have no intimate knowledge of is, to say the least, tricky.
Lightrun is a new kind of debugger.
It’s one geared specifically towards real-life production environments. Using Lightrun, you can drill down into running applications, including 3rd party dependencies, with real-time logs, snapshots, and metrics.
Learn more in this quick, 5-minute Lightrun tutorial:
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:
DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema.
The way it does all of that is by using a design model, a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database.
And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.
The Kubernetes ecosystem is huge and quite complex, so it’s easy to forget about costs when trying out all of the exciting tools.
To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.
Connect your cluster and start monitoring your K8s costs right away:
We’re looking for a new Java technical editor to help review new articles for the site.
1. Introduction
In this quick tutorial, we’re going to examine the differences between the PermGen and Metaspace memory regions in the Java environment.
It’s important to keep in mind that, starting with Java 8, the Metaspace replaces the PermGen – bringing some substantial changes.
2. PermGen
PermGen (Permanent Generation) is a special heap space separated from the main memory heap.
The JVM keeps track of loaded class metadata in the PermGen. Additionally, the JVM stores all the static content in this memory section. This includes all the static methods, primitive variables, and references to the static objects.
Furthermore, it contains data about bytecode, names, and JIT information. Before Java 7, the String Pool was also part of this memory. The disadvantages of the fixed pool size are listed in our write-up.
The default maximum memory size for 32-bit JVM is 64 MB and 82 MB for the 64-bit version.
However, we can change the default size with the JVM options:
- -XX:PermSize=[size] is the initial or minimum size of the PermGen space
- -XX:MaxPermSize=[size] is the maximum size
Most importantly, Oracle completely removed this memory space in the JDK 8 release. Therefore, if we use these tuning flags in Java 8 and newer versions, we’ll get the following warnings:
>> java -XX:PermSize=100m -XX:MaxPermSize=200m -version OpenJDK 64-Bit Server VM warning: Ignoring option PermSize; support was removed in 8.0 OpenJDK 64-Bit Server VM warning: Ignoring option MaxPermSize; support was removed in 8.0 . With its limited memory size, PermGen is involved in generating the famous OutOfMemoryError. Simply put, the class loaders weren’t garbage collected properly and, as a result, generated a memory leak.
Therefore, we receive a memory space error; this happens mostly in the development environment while creating new class loaders.
3. Metaspace
Simply put, Metaspace is a new memory space – starting from the Java 8 version; it has replaced the older PermGen memory space. The most significant difference is how it handles memory allocation.
Specifically, this native memory region grows automatically by default.
We also have new flags to tune the memory:
- MetaspaceSize and MaxMetaspaceSize – we can set the Metaspace upper bounds.
- MinMetaspaceFreeRatio – is the minimum percentage of class metadata capacity free after garbage collection
- MaxMetaspaceFreeRatio – is the maximum percentage of class metadata capacity free after a garbage collection to avoid a reduction in the amount of space
Additionally, the garbage collection process also gains some benefits from this change. The garbage collector now automatically triggers the cleaning of the dead classes once the class metadata usage reaches its maximum metaspace size.
Therefore, with this improvement, JVM reduces the chance to get the OutOfMemory error.
Despite all of these improvements, we still need to monitor and tune the metaspace to avoid memory leaks.
4. Summary
In this quick write-up, we presented a brief description of PermGen and Metaspace memory regions. Additionally, we explained the key differences between each of them.
PermGen is still around with JDK 7 and older versions, but Metaspace offers more flexible and reliable memory usage for our applications.
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes: