[Lustre-devel] Feed API and Changelog HLD

Peter J Braam Peter.Braam at Sun.COM
Tue Feb 5 05:43:48 PST 2008

Nathaniel Rutman wrote:
> Peter J Braam wrote:
>> On page 10 of the changelog API: recursive behavior for directories 
>> in filesets must exclude directories that are mount point of other 
>> filesets (as implemented for the Path Forward a few years back).
>> I didn't see where ABORT sizes are discussed, but as I mentioned 
>> before there are few cases where ditching records is possible.
> I don't know what you're talking about with ABORT - you mean e.g. HSM 
> should
> abort copying an old file if the file is modified after the copy 
> starts?  Or something else?
Hmm, this was my jetlagged head, sorry.  I meant when you want to force 
a truncation of the log (and throw records away), how you do handle 
this?  You need this mechanism, even though it will be used only rarely.

While I am writing this, I also realize that there are some logs that 
may require re-compacting.  This happens for the LRU logs (tracking most 
recent access to files for HSM migration management) I think.  The idea 
for these logs is to (1) append a new record when an object is accessed, 
and (2) cancel the previous record for that object using a pointer to 
that record in the object.  These records can be tiny (obj id / parent 
obj id), but the mechanisms causes llog files to be non-empty with holes.

>> The storage of the records should be discussed.  The llog headers may 
>> need changes and probably the API's for canceling records will change 
>> to indicate what consumer is canceling.
>> It would be wise to discuss how disk full failures etc are handled in 
>> some detail.
> ok.  Does it seem to be on the right track in general now?
At a 10,000 feet level yes.  My concerns at this point are error 
handling and performance and multiple consumer management. That's not so 
clear yet.

- Peter -

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