On Wed, Feb 24, 2021 at 9:10 AM 조규진 <bori19960(a)snu.ac.kr> wrote:
I'm a newbie in CephFS and I have some questions about how per-MDS journals
In Sage's paper (osdi '06), I read that each MDSs has its own journal and
it lazily flushes metadata modifications on OSD cluster.
What I'm wondering is that some directory operations like rename work with
multiple metadata and It may work on two or more MDSs and their journals,
so I think it needs some mechanisms to construct a transaction that works
on multiple journals like some distributed transaction mechanisms.
Could anybody explains how per-MDS journals work in such directory
operations? or recommends some references about it?
Your intuition is correct: these transactions span multiple MDS journals.
The code for this stuff is somewhat long, in src/mds/Server.cc, but
here are a couple of pointers if you're interested in untangling it:
- Server::handle_client_rename is the entry point
- The MDS which handles the client request sends MMDSPeerRequest
messages to peers in rename_prepare_witness, and waits for
acknowledgements before writing EUpdate events to its journal
- The peer(s) write EPeerUpdate(OP_PREPARE) events to their journals
during prepare, and EPeerUpdate(OP_COMMIT) after the first MDS has
> ceph-users mailing list -- ceph-users(a)ceph.io
> To unsubscribe send an email to ceph-users-leave(a)ceph.io