[Lustre-devel] Commit on share

[Peter Braam]

On 6/11/08 8:21 AM, "Alexander Zarochentsev"
<Alexander.Zarochentsev at Sun.COM> wrote:

> Hello,
> 
> On 27 May 2008 14:44:18 Peter Braam wrote:
>> This HLD is definitely not ready at all.  It is very short, lacks
>> interaction diagrams and the arguments made are not sufficiently
>> detailed.
> 
> is the following definition of dependent operation more clear?
> 
> Operation B depends on operation A if:
> 
> 1. A and B modify the same object
> 2. B modifies the object after A (LDLM serializes object access)
> 3. A isn't committed yet
> 4. A and B are issued by different clients

This shows a fundamental mistake, and one I was afraid of.  If a second
client only reads uncommitted data there is already a dependency.

You need to read the database literature - this is standard stuff, here is a
link to a great book:

http://research.microsoft.com/~philbe/ccontrol/

Peter


> 
>> * the second sentence is not right.  Commit should happen before
>> un-committed data coming from a client is shared with a 2nd client.
>> * Is COS dependent on VBR ­ no it is not, and can equally apply to
>> normal recovery
>> * Section 3.2 is wrong: the recovery process will not fail with gaps
>> in the sequence when there is VBR.  It only fails if there are gaps
>> in the versions, and this is rare.
>> * 3.3 parallel creations in one directory are protected with
>> different, independent lock resources.  Isn¹t that sufficient to
>> allow parallel operations with COS?
> 
> The objects in the definition of dependent operation can be those parts
> of the directory identified by hash.
> 
>> * 3.6 provide a detailed explanation please
>> * GC thread is wrong mechanism this is what we have commit callbacks
>> for * Why not use the DLM, then we can simply keep the client waiting
>> ­ the mechanism already exists for repack;
> 
> CoS is just an improved version of rep-ack, using persistent storage
> instead of client replay queue?
> 
>> I am not convinced at all
>> by the reasoning that rep-ack is so different ­ no real facts are
>> quoted * It is left completely without explanation how the hash table
>> (which I think we don¹t need/want) is used
>> 
>> Regards,
>> 
>> Peter
> 
> Thanks,