[Lustre-devel] Recovering opens by reconstruction

[Alex Zhuravlev <Alex.Zhuravlev@Sun.COM>]

Andreas Dilger wrote:
>> my old thougth was that instead of introducing special new open-by-fid RPC
>> we should try to implement open in terms of LDLM locks because it's in-core
>> state (though with specific tracking of unlinked files). given this we'd
>> automatically get single mechanism for all in-core states and we'd get rid
>> of special paths for open replays.
> 
> One problem with this is that the ordering needs to be preserved.  Opens
> that have committed need to be replayed before any other replay operations,
> because those replayed operations may depend on the file being open.
> However, "normal" lock replay should happen after (or conceivably during)
> operation replay so that the objects being locked actually exist and the
> server can (hopefully soon) verify the lock version number during recovery.

well, that ordering is already "dead" due to VBR?

I think semantics of unlink is just to unlink name, everything else is up to
MDS (when to destroy inode and objects). also notice inode destroy is a different
transaction in general (due to possible multi-transaction truncate).

if we decouple unlink and object destroy, then the following sequence should work:
1) replay on-disk states
    (unlink just put inode onto orphan list)
2) replay in-core states
    (including open locks)
... at some point
3) MDS goes over orphan list and destroys selected objects
    (depending on VRB policy, etc)

thanks, Alex