view

ClearCase data structure

APPLICABILITY

ClearCase (data structure), Attache (data structure)

SYNOPSIS

Windows NT directory tree created by mkview command

DESCRIPTION

A view provides a workspace in which users can access versions of ClearCase elements and other file-system objects that are outside of ClearCase source control. There are two kinds of views:

• Dynamic views, which provide transparent access to versions of elements in the VOB and to view-private objects. Each time you access an element through a dynamic view, the view's view_server process evaluates the view's config spec and selects a particular version of the element. Thus, such a view updates itself with new versions created in other views.
• Snapshot views, which contain copies of versions of specified elements, along with view-private objects. The view never updates itself with new versions created from other views. Instead, the update command reevaluates the view's config spec and loads the newly selected versions into the view.

This reference page discusses both a view's physical data structures and the way file system data appears to a user process through a view. Each type of view is discussed separately.

Dynamic Views: The File System

A dynamic view is an MVFS ( multiversion file system) directory tree that enables dynamic access to VOB elements.

Dynamic Views: View Storage Directory

A dynamic view is implemented as a standard directory tree, whose top-level directory is termed the view storage directory. The directory contains these files and subdirectories:

Dynamic Views Private Storage Area

Subdirectory .s of the view storage directory is the root of a subtree that implements the view's
private storage area. The private storage area holds several kinds of objects:

VIEW-PRIVATE OBJECTS. A view-private object is a file-system object-file or directory-created by a standard program within a VOB directory. Such objects are stored only within the view's private storage area. No VOB maintains any record of such objects.

CHECKED-OUT FILES. A checked-out version is a file created by the checkout command. This file is an editable copy of the version being checked out.

A checked-out version is very much like a view-private file, except that there is a corresponding object in the VOB database: the special "placeholder" version with the CHECKEDOUT version label.

UNSHARED DERIVED OBJECTS. An unshared derived object is a data container created by execution of a makefile build script by clearmake, omake, or by any program invoked by clearaudit. A corresponding derived object is created in the VOB database if you are using a dynamic view.

NOTE: An unshared derived object remains in the view's private storage area even after the DO becomes shared. Promotion of the DO involves copying, not moving, the data container. The winkin command and view_scrubber utility remove unshared derived objects from a view's private storage area.

NONSHAREABLE DERIVED OBJECTS. A nonshareable derived object is a data container created by execution of a makefile build script by clearmake, omake, or by any program invoked by clearaudit, from a dynamic view. No information about the DO is stored in the VOB database. When you use winkin or view_scrubber -p to convert a nonshareable DO to a shareable DO, the command promotes the DO's data container to the VOB, and removes the data container from view storage.

CONFIGURATION RECORDS. The file view_db.crs_file in the .s subdirectory is actually part of the view's database, as described in the following section. It is the part that stores the configuration records of derived objects built in the view.

STRANDED FILES. The directory lost+found in the .s subdirectory contains stranded files, that is, files that were view-private and are no longer accessible through normal ClearCase or Attache operations. (Only dynamic views have lost+found directories.) A file becomes stranded when there is no VOB pathname through which it can be accessed. For example:

• A VOB can become temporarily unavailable, for example, by being unmounted.
• A VOB can become permanently unavailable, for example, by being deleted.
• A VOB directory can become permanently unavailable, by being deleted with a rmelem command.

See the description of the recoverview command for more information about recovering stranded files (recoverview does not apply to snapshot views.)

Dynamic Views: View Database

The view database subdirectory, db, contains these files:

The view database keeps track of the objects in its private storage area: view-private objects (files, directories, and links), checked-out versions, nonshareable derived objects, and unshared derived objects.

Snapshot Views: The File System

The snapshot view directory tree is part of the native file system (as opposed to the directory tree of a dynamic view, which is part of the MVFS, or multiversion file system). In addition to copies of ClearCase elements, the root of this directory tree (referred to as the snapshot view's root directory) contains the following files and subdirectories:

NOTE: When referring to a snapshot view, many ClearCase commands require the snapshot-view directory-pname (as opposed to the view's view-tag). By reading the view's view.dat file, which is in the root directory of the snapshot view, ClearCase can find all of the files and directories associated with the view.

Snapshot Views: View-Storage Directory

The view-storage directory (by default, view.stg), is used by ClearCase to maintain the view. It contains the following files and subdirectories:

Snapshot Views: View Database

The view database subdirectory, db, contains these files:

For a snapshot view, the view database keeps track of the loaded VOB objects and checked-out versions in the view.

Comparison of Dynamic and Snapshot Views

Snapshot views:

• Require an update operation periodically

• Provide optimal performance for developing source files and for prototype builds
• Facilitate working from a remote location
• Use the load command to copy a specified set of source files into the view

Work in a snapshot view when any of these conditions is true:

• You want to optimize build performance to achieve native build speed.
• You want to work with source files under ClearCase control when you are either disconnected from the network or connected to the network intermittently from a remote location.
• You want to access a view from a computer that is not a ClearCase host.
• Your development task doesn't require the ClearCase build auditing and build avoidance features.

Dynamic views:

• Show changes to elements in the VOB as they are made (and thus do not require an update operation)
• Support the ClearCase build auditing and build avoidance features
• Provide access to all elements in all mounted VOBs without using load

Work in a dynamic view when any of these conditions is true:

• Your development task requires audited builds.
• You want to enable derived object sharing.

  You can use express builds to enable DO reuse in your view, but not allow the DOs to be winked in by other views. For more information, see Derived Objects and Configuration Records in Building Software with ClearCase.

• You prefer to use a view that is updated during development.

Table 13 compares features of snapshot views and dynamic views.

SEE ALSO

config_spec, endview, load, lsview, mkview, mvfsstorage, recoverview, reformatview, registry_ccase, scrubber, startview, update, view_scrubber, vob