my comments to:
5. Inter-Replica Communication
are marked with #:
5.1 Batch Driven Mirror Replication
Authoritative reference:
This memo.
Description:
In this model, the replica web server to be updated
initiates communication with a master origin web server.
# shouldn't it be: "replica origin server"
# and: "master origin server" to be consistent with
# the terminology introduced earlier
# also I know examples where the transfer
# is inititated by the master not the replica.
The communication is established at intervals based upon
queued transactions which are scheduled for deferred
processing. The scheduling mechanism policies vary, but
generally are reoccuring at a specified time. Once
communication is established, data sets are copied to the
initiating replica web server.
Security:
Relies upon the protocol being used to transfer the data
set. FTP and RDIST are the most common protocols observed.
# if this is about *web* replication practice
# than my experience is that most popular protocols
# in use would be FTP, rsync and HTTP.
# CVSUP and rdist are also used, but rather seldomly
Deployment:
Very common for mirror synchronization in the Internet.
Submitter:
Document editors.
5.2 Demand Driven Mirror Replication
Authoritative reference:
This memo.
Description:
In this model, the replica web server acquires the content
as needed due to demand. This is generally done by web
server accelerators (reverse proxy) operating as origin
server replicas. When a web client requests a URL that is
not in the data set or the replica origin server, the
replica server attempts to acquire it from a master origin
server and forwarded on to the requesting web client.
# here I'm confused - this is specific to caching,
# not web replication in general. why is it in this section ?
Security:
Relies upon the protocol being used to transfer the URLs.
FTP, Gopher, HTTP and ICP are the most common protocols
observed.
# i doubt if gopher or ftp is used to transport www objects ?
Deployment:
Observed at several large web sites. Extent of usage in
the Internet is unknown at this time.
Submitter:
Document editors.
5.3 Synchronized Replication
Authoritative reference:
This memo. [Ed note; there is no IETF protocol specified at
this time. The editors are aware of at least
two open source protocols, AFS and CODA, along
with one expired IETF draft
<draft-leach-cifs-v1-spec-01.txt> and one
proprietary protocol Novell NRS; none of which
can be considered an authoritative reference]
Description:
In this model, the replicated origin servers cooperate
using synchronized strategies and specialized replica
protocols to keep the replica data sets coherent.
Synchronization strategies range from tightly coherent (a
few minutes) to loosely coherent (a few or more hours).
Updates occur between replicas based upon the
synchronization time constraints of the coherency model
employed and are generally in the form of deltas only.
# isn't it about distributed file systems like DFS, AFS etc ?
# i think it's beyond the scope of this document.
# otherwise we should consider network file system as well
# like cached NFS or WebNSF
--w
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