On 07/12/2017 00:19, James Roper wrote:
:
One issue that I'm not sure about is the consequences of using direct
buffers with regards to garbage collection. If direct buffers are
never copied onto the heap, and are never reused, lets say you're just
implementing a proxy passing buffers through from one connection to
another, then the heap usage of the application may be very small, and
this could mean that garbage collection is done very infrequently. As
I understand it, this can result in direct buffers staying around for
a long time, and possibly causing the system to run out of memory.
Does anyone have any experience with that, and how to deal with it? We
don't generally have this problem in Akka because we always copy our
buffers onto the heap into an immutable structure, so even if we do
use direct buffers and don't reuse them, our heap usage grows at least
as fast as our direct buffer usage grows, which means total memory
usage won't exceed twice the size of the heap since eventually garbage
collection will clean both up.
This thread is getting a little off-topic but just to say that you can
limit the amount of memory reserved for direct buffers. Attempts to
allocate further direct buffers will trigger GC and reference
processing. Yes, this can be expensive. This area improved significantly
in JDK 9 so that the retry coordinates with the reference processing and
mostly avoids spurious OOME that were possible with older releases.
-Alan
