[Lustre-devel] Queries regarding LDLM_ENQUEUE

[Paul Nowoczynski <pauln@psc.edu>]

bzzz.tomas at gmail.com wrote:
> On 10/20/10 8:43 PM, Paul Nowoczynski wrote:
>   
>> It's for scalability reasons. When N clients traverse the namespace with
>> the purpose of opening the same file the result is a storm of RPC
>> requests which bear down on the metadata server. This type of activity
>> becomes prohibitive especially when you start considering client counts
>>  > 10^4. An operation such as this is ripe for optimization because
>> every client in the network is trying to build the same state. If you
>> have a method for a single client to 'learn' the final state, i.e. the
>> pathname -> fid translation, and broadcast it to its cohorts, it's a
>> huge win because it eliminates an O(N) operation.
>> paul
>>     
>
> clear enough, but what is the bottleneck here: MDS to handle lots of
> RPCs or network to pass RPCs ?
I could be wrong but my guess is that the network congestion caused by 
this communication pattern is a more serious problem.  The mds should be 
able to easily service lookup rpc's since only the first few necessitate 
a read I/O from the disk.
> thanks, z
>
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