On Wed, Feb 24, 2021 at 9:10 AM 조규진 <bori19...@snu.ac.kr> wrote: > > Hi. > > I'm a newbie in CephFS and I have some questions about how per-MDS journals > work. > 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 completed. John > > Thanks. > kyujin. > _______________________________________________ > ceph-users mailing list -- ceph-users@ceph.io > To unsubscribe send an email to ceph-users-le...@ceph.io _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
