Thomas,
On 1/20/22 04:16, Thomas Hoffmann (Speed4Trade GmbH) wrote:
just one remark: Take care about the 32 GB. Configuring more than 32 GB, the
Java Pointers will use 64 Bit and thus need double the space.
Thus 34 GB memory can be worse than 31 GB.
See also
https://blog.codecentric.de/en/2014/02/35gb-heap-less-32gb-java-jvm-memory-oddities/
Just my 2 cents.
While this is indeed true (and can be surprising), it is not relevant.
Nobody with 16GiB of physical memory has any business attempting to use
a 32GiB heap.
-chris
-----Ursprüngliche Nachricht-----
Von: Olaf Kock <tom...@olafkock.de>
Gesendet: Donnerstag, 20. Januar 2022 09:54
An: users@tomcat.apache.org
Betreff: Re: Tomcat dedicated server
Hi Lance
On 19.01.22 23:35, Campbell, Lance wrote:
On a Tomcat 9.x dedicated Linux server with 16G of memory, how much memory
would you allocate for the OS?
Assume there is no file processing taking place. Also assume Tomcat is
communicating primarily with a PostgreSQL database and Apache web server each
running on their own dedicated servers. The Tomcat application server is the
only thing running on the Linux server.
It depends (TM)
Without knowing your application, the load (e.g. number of concurrent
users) and general setup, there's no way to tell. I'd rather handle the
question the other way around: How much memory does (your application
on) Tomcat require. Tomcat itself is happy with just a little bit of memory,
but applications vary widely. Also, some applications are memory-bound, some
are I/O-bound, some are CPU-bound. So memory might not be your bottleneck to
worry about.
You should load-test your application with a realistic load (plus
margin) and keep an eye on memory consumption. But in the end you'll find out
what is the first bottleneck to appear. It might not be memory.
But to come back closer to your original question: I recommend to deactivate
swapspace for production servers, and configure -Xms equal to -Xmx, so that you
find shortages of memory early (when you start the
application) rather than Sunday night at 3am. You might want to leave 1-2G for
the OS and start testing this way, or rather test how little memory your app
requires to run and add margin. My rule of thumb is: The more memory there is
to be claimed in GC, the longer a full GC run takes. Often, many short but
frequent GC runs are preferable to fewer but longer lasting. (I didn't check if
this still applies to the newer generation of garbage collectors, so take this
GC-statement with a grain of salt)
Olaf
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