3:29 a.m.
Hi Ben,
why don't you post an edited version of my private replies to you to
this topic as well, so we have some background ?
In a nutshell, you want to use a zero-copy transport between processes
that run on the *same physical box* (e.g. shipping only pointers to
native shared memory between processes). Currently, using TCP or UDP
between processes on the same box still requires 1 or 2 copies, even
when a loopback device is used.
I'm interested in adding such a transport in JGroups 4, in which I plan
to revamp the transport to adopt an NIO based scheme, accommodating both
TDP and TCP. This is all still in the planning phase, but one feature
will be to have multiple transports running in the same stack and
sending messages alternatively via different transports. E.g. multicasts
would use UDP whereas unicasts would use TCP (by default), but this
could be overridden per message (with flags).
If we then had 5 physical boxes, with 20 processes on each box, for a
total of 100 nodes, then we could configure the stacks to run both
SHR_MEM and UDP: a group-wide message (a multicast) would be sent via
SHR_MEM *and* UDP.
The SHR_MEM transport would disseminate the message to all 20 processes
on the same physical box, using shared memory. The UDP transport would
be configured as non-loopback (IP_MULTICAST_LOOP=false), which means
that the message would be multicast to the other 3 physical boxes, but
the local multicast would be dropped. The other boxes would then use
SHR_MEM to disseminate the message locally to all 20 processes.
Just an idea atm, this could also be done via RELAY2, but the QoS would
not be the same.
I'm planning on releasing 3.5 in 6-8 weeks from now. This includes a
community baking phase during which I'll be working on a deep-dive
course on JGroups.
So a *very tentative* schedule is to start on 4.0 at the beginning of
summer.
On 28/02/14 19:16, cotton-ben wrote:
Hi Mircea, Manik, Bela, et. al.
I want to more publicly muse on this SUBJ line. Here now, then maybe in
ISPN /user/ forum, then maybe JSR-347 provider wide. I know we had a
semi-private (Bela led) exchange, but I want to be more public with this
conversation.
Long post again. sorry.
This is just on open musing. I realize this musing should not expect to be
accommodated by any "oh, we got to do this in ISPN/JGRPs now!" repsonse ...
there is absolutely only the most infrequent use-case that would /today/ be
served by addressing this musing ... but tomorrow that /will/ be a different
story.
Questions::
Does the concept of ISPN/JGRPs transport between "Cluster" nodes currently
depend on OSI transport layer sockets' participation(s)?
In other words, if all the nodes on my "Cluster" have locality=127.0.0.1 is
ISPN/JGRPs accommodating enough to use a native OS IPC choice as an
intra-node transport?
Or, is it true that my transport choices are always limited to just
{TCP,UDP} -- independent of the participating nodes' locality (and that I
am thus forced to go over an OSI loopback)?
If my transport choices are only limited to {TCP,UDP} for all node locality,
then I might ask that you consider additional upcoming modern Java transport
options.
With the ambitions of upcoming OpenJDK JEPs, that will make mainstream an
API capabilty that today is only available via sun.misc.Unsafe, Java will
soon have "more complete" transport options that will include all of
{ TCP, UDP, RDMA/SDP, IPC }
Some examples of upcoming accommodating providers=
1. RDMA/SDP: via Infiniband VERBS (works today in JDK 7 on OSI physical
layer IB NICs, does not work over Ethernet)
2. IPC via OpenHFT' SHM as IPC solution (will work this year)
Again, I realize that these transport choices are useful today only in a
very rare use case. However, should these transports be in your offering to
ISPN/JGRPs customers, then ISPN/JGRPs becomes -- like all of Java has
become in recent years -- increasingly more attractive to /all/ HPC Linux
supercomputing use cases (not just ours).
--
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Bela Ban, JGroups lead (http://www.jgroups.org)