max heap size for compressed oops

Martijn Verburg martijnverburg at
Wed Dec 9 16:27:55 UTC 2015

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

Mechanical Sympathy:!forum/mechanical-sympathy
Friends of jClarity:!forum/friends


On 9 December 2015 at 16:04, Matthias Wahl <matthiaswahl at> 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.
> mention an
> upper limit of 32GB.
> Howerer the elasticsearch documentation recommends to not increase the
> heap size beyond 30.5GB :
> 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.

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