From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Nowoczynski Date: Wed, 20 Oct 2010 13:11:58 -0400 Subject: [Lustre-devel] Queries regarding LDLM_ENQUEUE In-Reply-To: <4CBF1D82.60508@gmail.com> References: <4CBEA415.80307@gmail.com> <9C26CBA7-8DBD-4875-8E14-FB663B749096@oracle.com> <4CBEA8A9.9080802@gmail.com> <00d001cb705a$fd64cb80$f82e6280$@com> <4CBF01DA.3090505@psc.edu> <4CBF094A.9020302@gmail.com> <4CBF1C42.1090109@psc.edu> <4CBF1D82.60508@gmail.com> Message-ID: <4CBF22DE.9080204@psc.edu> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lustre-devel@lists.lustre.org 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 > > _______________________________________________ > Lustre-devel mailing list > Lustre-devel at lists.lustre.org > http://lists.lustre.org/mailman/listinfo/lustre-devel >