max heap size for compressed oops

[Martijn Verburg]

Hi Matthias,

OpenJDK mailing lists are (primarily) for discussions on technical work of
OpenJDK itself.  You may get some joy out of the hotspot-dev mailing list
but you're probably better off trying one of the following performance
communities:

Mechanical Sympathy:
https://groups.google.com/forum/#!forum/mechanical-sympathy
Friends of jClarity:
https://groups.google.com/a/jclarity.com/forum/#!forum/friends




Cheers,
Martijn

On 9 December 2015 at 16:04, Matthias Wahl <matthiaswahl at m7w3.de> wrote:

> Hello,
>
> i was delving into performance considerations that some java based
> projects suggested. One is restricting the maximum heap size on 64 bit
> systems due to the limitation on compressed Oops. The docs e.g.
> https://wiki.openjdk.java.net/display/HotSpot/CompressedOops mention an
> upper limit of 32GB.
>
> Howerer the elasticsearch documentation recommends to not increase the
> heap size beyond 30.5GB :
>
> https://www.elastic.co/guide/en/elasticsearch/guide/current/heap-sizing.html#compressed_oops
>
> it's the only source i know using this recommendation.
> They recently changed it due to an advice from oracle, they say. but no
> reason why is given.
>
> Do you know any reason for limiting the heap size to 30.5 GB instead of
> 32 GB?
>
> thanks in advance!
>
> Matthias Wahl
>
> this is kind of a cross-post as it was already asked on IRC. But I'll
> repeat it here, so any answer may persist for others having the same
> question.
>