OSF DCE Administration Guide--Core Components

Chapter 14. How CDS Updates Data
Once names exist in the namespace, users who have the appropriate access can make
changes to the data associated with the names. Any addition, modification, or deletion of
CDS data initially happens in only one replica: the master replica. This chapter
introduces the main methods by which CDS keeps other replicas consistent: update
propagation and the skulk operation. It also describes two timestamps that help to ensure
consistency in CDS data. By understanding the concepts in this chapter, you can more
effectively plan the content and replication of directories and the organization of
hierarchical cells in your namespace.
14.1 Update Propagation
An update propagation is an immediate attempt to apply one change to all replicas of the
directory in which the change was just made. Its main benefit is that it delivers each
change in an efficient and timely way.
Unlike a skulk operation, however, update propagation does not guarantee that the
change gets made in all replicas. If a particular replica is not available, the update
propagation does not fail; the change simply does not get made in that replica. The skulk
operation ensures that, when the replica is available again, it becomes consistent with the
other replicas in its set.
You can tune the degree of persistence that CDS uses in attempting an update
propagation—or prevent propagation altogether—by adjusting a directory attribute
called CDS_Convergence. Convergence also affects the frequency of skulks on a
directory. (See Chapter 18 for details on viewing and changing a directory’s
convergence.)
14.2 Skulk Operation
The skulk operation is a periodic distribution of a collection of updates. Its main
functions are to ensure that replicas receive changes that may not have reached them
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