Hi all,
I just released a new version of SSG (v0.3) over the weekend, and wanted
to give you a heads up on the major changes included in this release.
It's been a while since SSG has been updated, so there's a lot to mention...
1.) SSG no longer identifies group members using dense ranks (i.e.,
ranks 0...n-1), and instead identifies members using hashes of their
Mercury addresses, meaning group members will now have unique
identifiers across groups
2.) To allow users to keep using dense-ranked style access to a group's
membership information, SSG additionally creates a sorted list of member
IDs associated with a group, and allows users to access this info using
ranks into the sorted list, rather than member IDs.
3.) We have renamed group "attachers" to group "observers" (and modified
corresponding function/constant names), with the semantics of these
functions being the identical: providing clients access to group
information without becoming proper group members.
3.) SSG now supports the ability for processes to dynamically leave/join
previously created SSG groups, with SSG extending the SWIM failure
detection protocol to propagate this info out to the group. Other group
members get callback notifications on newly joined or left members, just
the same as it does for failed group members.
3.) A new PMIx-based bootstrapping mechanism has been implemented,
allowing SSG to utilize PMIx process information for bootstrapping
groups of processes on systems with PMIx-compatible process launchers.
4.) On systems that support PMIx, SSG additionally registers for event
notifications on any process/node failures that might affect a job, with
SSG immediately evicting affected group members.
As you might expect, the API has changed quite a bit to accommodate all
of these modifications. I'm not going to enumerate here, but please have
a look at the new headers to get a feel for what has changed and how to
take advantage of new capabilities. I'm also attaching slides for the
SSG tutorial I'll be presenting at the Mochi bootcamp this week, which
should be helpful in covering the new API. Please have a look and let me
know if you have any questions, comments, or concerns.
I have already made a pass through the Spack sds-repo to make sure our
packages are aware of the new SSG version and so that other packages
(Mobject, Benvolio) are not using the new version until we've had time
to port them over.
Thanks!
--Shane
