Updates to JEP-158: JVM Unified Logging are coming...

Mattis Castegren mattis.castegren at oracle.com
Fri Apr 17 13:16:32 UTC 2015

I guess it would be a possible later enhancement request to add a new logging tag ”gc_compressed” for example that prints gc output in some easy to parse format. It could be one line of comma separated values per GC for example that you could import to other tools.


But I agree with Fredrik, we should look at exactly what problems you try to solve, and see if it instead can be solved in JFR. You could make a recording that only gathers GC data, and you could run it for days and still get a pretty small recording (at least smaller than what a corresponding gc log would be). If you then still feel the need to import the data to some other tool, maybe we should add that tool’s functionality to Mission Control?


Kind Regards



From: Fredrik Arvidsson 
Sent: den 17 april 2015 14:36
To: Martijn Verburg
Cc: serviceability-dev at openjdk.java.net serviceability-dev at openjdk.java.net; hotspot-dev at openjdk.java.net Source Developers
Subject: Re: Updates to JEP-158: JVM Unified Logging are coming...


Hi Martijn, and the others :)

I'm glad you like what we do. We also think the tag based logging is something good, and that it will make the logging in the JVM easier to implement, configure and consume.

Regarding 'binary / compressed' log format. We are not planning to add any structured log format to the unified logging framework. It is outside the scope of this JEP. The log data format is a simple string with some well defined decorations. The logs are primarily meant to be read by humans.

There will be log output extension points in the framework, but they will not be accessible publicly and they will not support 3rd party extensions in runtime. Even if the output extension API would be made fully accessible, the data fed in to it would still only be a string, since thats what the developers are adding in the code where the logging framework is called. I guess one could add compression of log data as an extension, but I don't think that is really what you are asking for.

As you might know, Oracle offers low latency low intrusive structured logging in its Java Flight Recorder product. We are not aiming in this JEP to overlap that functionality more than absolutely needed.


On 2015-04-17 12:12, Martijn Verburg wrote:

Hi Fredrik, 


Thanks from us (jClarity and some other orgs) for considering the tag based system, we're really glad you've gone in this direction.  One quick bit of feedback.


Is it possible to add a binary / compressed logging format or an interface/ API to plug one in for high performance Logging?  Human readable is nice for looking at logs immediately, but for some of our customers they'd be looking to offload that concern to another process/host.



On 17 April 2015 at 09:32, Fredrik Arvidsson <HYPERLINK "mailto:fredrik.arvidsson at oracle.com" \nfredrik.arvidsson at oracle.com> wrote:


We are planning to release an updated version of JEP-158 very soon. The work to update this JEP has been going on for some time and we now feel we are ready to present it to a wider audience.

The JEP for JVM Unified Logging was created back in February 2012. The requirements for the API and implementation were heavily influenced by the logging functionality in JRockit JVM. The JEP was updated and refined in mid 2014 and eventually targeted for JDK 9 in late 2014:

During the review process of the JEP some concerns were voiced about the chosen API and functionality but the conclusion was that the proposal would work, and the JEP was targeted for JDK 9 and the implementation work was started.

Early 2015 during pre-reviews and presentations of the API and implementation concerns were again raised about the formulation of the JEP, this time with greater force. At this point we decided to take a time-out and investigate our options going forward.

The time-out led to a modified proposal that can be found here:
HYPERLINK "http://cr.openjdk.java.net/%7Efarvidsson/JEP-158/JEP-158.html" \nhttp://cr.openjdk.java.net/~farvidsson/JEP-158/JEP-158.html
and with some illustrations here:
HYPERLINK "http://cr.openjdk.java.net/%7Efarvidsson/JEP-158/JEP-158_Illustration.png" \nhttp://cr.openjdk.java.net/~farvidsson/JEP-158/JEP-158_Illustration.png

So what have we changed, and why?
In short we have switched from using an hierarchical log subject layout to something that could be best described as a tag based solution.

The main reason for the change of the logging API is that we have found that some logging can't easily be ordered under a single hierarchical subject but can belong to multiple subjects/areas. One example of this is logging in the 'metaspace' code. The functionality in the 'metaspace area' can be called from both GC and Runtime code. Another example is class-unloading. There are more examples on this of course, but these two we think are very clear and easy to understand.

The core functionality of the logging framework is not changed that much from the earlier proposal. We have tried to make it leaner and not as verbose (functionality wise) as before. The scope of the implementation has been narrowed down some to enable us to deliver good value as soon as possible.

Our plan is as follows:
After getting initial feedback from the community about the new proposal we will update the JEP description. We aim to do this early next week.
We are planning to use the JDK9 sandbox repository during development. This enables us who are implementing it to work in an efficient way and at the same time it allows any interested party to try out and follow the work during the implementation phase.

More information about the sandbox repository name and other practicalities will follow shortly.

Fredrik Arvidsson & Marcus Larsson, JVM Serviceability, Stockholm.



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