[Gzz-commits] gzz/Documentation/misc/hemppah-progradu existin...

[Hermanni Hyytiälä]

CVSROOT:        /cvsroot/gzz
Module name:    gzz
Changes by:     Hermanni Hyytiälä <address@hidden>      02/11/12 02:39:22

Modified files:
        Documentation/misc/hemppah-progradu: existing_systems_overview 

Log message:
        Short overview of Coral (from the author)

CVSWeb URLs:
http://savannah.gnu.org/cgi-bin/viewcvs/gzz/gzz/Documentation/misc/hemppah-progradu/existing_systems_overview.diff?tr1=1.8&tr2=1.9&r1=text&r2=text

Patches:
Index: gzz/Documentation/misc/hemppah-progradu/existing_systems_overview
diff -u gzz/Documentation/misc/hemppah-progradu/existing_systems_overview:1.8 
gzz/Documentation/misc/hemppah-progradu/existing_systems_overview:1.9
--- gzz/Documentation/misc/hemppah-progradu/existing_systems_overview:1.8       
Mon Nov 11 08:29:08 2002
+++ gzz/Documentation/misc/hemppah-progradu/existing_systems_overview   Tue Nov 
12 02:39:21 2002
@@ -149,9 +149,53 @@
 
 Efficient peer-to-peer lookup based on distributed tries.
 
-hemppah: This is very interesting approach (tuomasl et all, comments ?) 
- 
+Author's comment ("Michael J. Freedman" <address@hidden>):
+
+- - -
+
+It is indeed submitted to IPTPS 03.  I'll probably make the whole paper
+public sometime in December if accepted.
+
+For now, here's a short overview:
 
+This paper presents Coral, a peer-to-peer content distribution system
+we are building. Coral is based on a new abstraction we call a
+\emph{distributed
+sloppy hash table} (DSHT) and is built as a layer on existing node lookup
+services~\cite{chord:ton,kademlia:iptps02,can:sigcomm01,pastry01,tapestry:tech}.
+Coral lets nodes locate and download files from each other by name.  Web
+caches can use it to fetch static data from nearby peers.  Users can
+employ it directly to share directories of files.  Coral's two principal
+goals are to avoid hot spots and to find nearby data without querying
+distant nodes.
+
+The DSHT abstraction is specifically suited to locating replicated
+resources.  DSHTs sacrifice the consistency of DHTs to support both
+frequent fetches and frequent stores of the same hash table key.  The
+fundamental observation is that a node doesn't need to know every
+replicated location of a resource---it only needs a single, valid,
+nearby copy.  Thus, a sloppy insert is akin to an append in which a
+replica pointer appended to a ``full'' node spills over to the
+previous node in the lookup path.  A sloppy retrieve only returns some
+randomized subset of the pointers stored under a given key.
+
+In order to restrict queries to nearby machines, each Coral node is a
+member of several DSHTs of increasing network \emph{diameter}.  We
+refer to these DSHTs as \emph{clusters}.  The diameter of a cluster is
+the maximum desired round-trip time between any two nodes it contains.
+When data is cached somewhere in a Coral cluster, any member of the
+cluster can locate a copy without querying machines farther away than
+the cluster's diameter.  Since nodes have the same identifiers in all
+clusters, even when data is not available in a low-diameter cluster,
+the routing information returned by the lookup can be used to continue
+the query in a larger-diameter cluster.
+
+Coral's challenge is to organize and manage these clusters in a
+decentralized manner.  As described in the next section, the DSHT
+interface itself is well-suited to locate and
+evaluate nearby clusters.  
+ 
+- - - 
 
 3. Different architectures for p2p networks: