On 22.02.2016 13:02, Gokul.Baskaran wrote:
The answer I expected is the JVM grows as much as to the available system
memory of there are m min and max set.
Gokul,
Well, no.
And because these messages get archived and searched later by other people, they may get
the wrong conclusion and therefore I will try again.
Re-read your last question.
And then re-read your question before that one.
And then re-read your question before that one.
The problem here is not that you are not being given the information that you
want.
The problem is that each time you ask your question, you ask it in a different way, and
each time somehow in a way that confuses people as to what exactly you want to know.
And the reason why it is confusing is that in your succesive questions you keep on talking
about "application memory" in various ways, but it is not clear what you are referring to
as "application".
For the OS, the JVM is an application.
For the JVM, Tomcat is the application.
And for Tomcat, the web applications (webapps) are the applications.
The JVM is one process that is running on a machine, under an OS.
That OS probably imposes limits on how much resources (including memory) a given process
is allowed to use. If a process tries to use more than this, it will be killed with an
"out of memory" error. It is unlikely that this per-process limit is "the available
system memory". The OS will kill the process before it uses all of that.
The JVM itself (of which there are various models on the market) uses memory in various
ways, for various purposes. One of these purposes is to manage a Heap, which it makes
available to Java applications which run inside the JVM.
But the JVM also uses memory for other reasons, such as a stack, and for the code of the
JVM itself.
For any given JVM, there are (probably) parameters which tell the JVM how much memory it
should set aside initially for the Heap, and then also for how big it should let the Heap
grow as a maximum. For the Oracle JVMs, these parameters are "-Xms" and "-Xmx".
By default (if these parameters are not set), the JVM uses some default values, which
/vary/ depending on the specific JVM and on the circumstances under which it is running
(the total available machine memory, for example).
For the Oracle JVM, someone already quoted to you the relevant documentation.
For other JVM's, you need to look at the relevant JVM documentation.
(You never indicated which JVM you are using).
The JVM runs java applications (of which Tomcat - the whole Tomcat - is one). These Java
applications cannot set the amount of memory that they will use in the Heap of the JVM,
other than indirectly (if they are well-written, the minimum necessary; if they are not
well-written, who knows). There is no Tomcat-level configuration option, that allows one
to set how much Heap space Tomcat can use within the JVM Heap.
Then within Tomcat, there are "web applications" running. Individual web applications
also cannot set how much Heap they will use, because is not "their" Heap, it is the
"Tomcat Heap", which itself is not really the Tomcat Heap, it is the JVM's Heap.
That Heap is used by /all/ web applications at the same time.
(That is a bit of an approximation, but ultimately it boils down to that).
So if one of the web applications within Tomcat starts to do things which result in
filling-up the Heap, and if the JVM cannot clean-up or increase the Heap anymore, there
will be problems, not only with that web application, but for all web applications and for
the whole Tomcat.
Is that clear, and does it answer your ultimate question ?
On Feb 22, 2016, at 2:43 AM, André Warnier (tomcat) <a...@ice-sa.com> wrote:
On 22.02.2016 03:44, Gokul.Baskaran wrote:
Thanks again, to make things clear. When I meant default, what is the default
min and max that is given to an application if there nothing defined in the JVM
?
In how many different ways do you need to be told this ?
Re-read the previous answers that you already received. All the information is
there.
In my case, the Tomcat is running on windows and I don't have setenv.bat or
sentenv.sh or even catalina.bat and catalina.conf does not have the OPT config
for min and max. HTH
Thank you
-Gokul
-----Original Message-----
From: Olaf Kock [mailto:tom...@olafkock.de]
Sent: Sunday, February 21, 2016 3:04 PM
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: Tomcat memory
grep mx bin/* found only settings in setenv.sh in my installation - this lets
me state that there are no defaults: setenv.sh is not contained in the
distribution but will be read in case it's found in the file system.
Thus there's no tomcat default that I'm aware of. Anybody who distributes
tomcat with a setenv.sh might have a sensible default for their embedded
application, but the raw distribution AFAIK has none.
Safe assumption should be: Whatever the JVM thinks is appropriate is the
default.
Create a setenv.sh or setenv.bat and set CATALINA_OPTS to the desired value, e.g.
"-Xms 2048m -Xmx2048m" (but there will probably be more settings, e.g. for
tuning the garbage collector...
(apologies in case this goes out after the problem has long been solved:
I'm in a hotel that blocks SMTP and have to find a way to send mail from
here)
Olaf
Am 21.02.2016 um 18:23 schrieb Gokul.Baskaran:
Question was for Java 7
It is a Tomcat / Application question as well, as memory default can be
configured in the application config.
I totally agree that the best practice is to set the Xms and -Xmx. As am going
to change the config, I would curious to know if the tomcat ui or the catalina
does not have a Xms and -Xmx, would it default to 400MB? I read this in another
forum.
-Gokul
-----Original Message-----
From: Olaf Kock [mailto:tom...@olafkock.de]
Sent: Sunday, February 21, 2016 3:14 AM
To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: Tomcat memory
This is rather a Java than a tomcat question:
The JVM allocates memory based on whatever default your current JVM
version decides (you don't mention what version of Java you're on)
From a text on
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics
.html
that's linked from my Java's manpage:
*initial heap size*
Larger of 1/64th of the machine's physical memory on the machine
or some reasonable minimum. Before J2SE 5.0, the default initial
heap size was a reasonable minimum, which varies by platform.
You can override this default using the |-Xms| command-line option.
*maximum heap size*
Smaller of 1/4th of the physical memory or 1GB. Before J2SE 5.0,
the default maximum heap size was 64MB. You can override this
default using the |-Xmx| command-line option.
*Note:* The boundaries and fractions given for the heap size are
correct for J2SE 5.0. They are likely to be different in subsequent
releases as computers get more powerful.
Note that this is from JavaSE7 and even mentions 5 - with more power there
comes more initial and maximum memory defaults.
I'm not aware of the actual development of the default memory - mostly
because I consider it good practice to know what an application uses
and provide it explicitly, rather than relying on defaults. (and
frankly, on the applications that I see, the default typically is not
even enough - let alone a good basis for tuning)
While we're at it: For production systems I consider it good practice to set -Xms and
-Xmx to the same value. Reason: If you don't have enough memory available, you want to
know this when the process starts, not days later when it tries to allocate "the
rest" - typically sunday night at 3am.
Olaf
Am 21.02.2016 um 03:39 schrieb Gokul.Baskaran:
Hi,
I am currently running tomcat 7 in Windows 2012.
The current JVM Heap memory parameters are set to empty, does the JVM Heap
memory utilize the entire memory of the OS or does it default to a specific
memory number?
Thank you
-Gokul
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