About ClearCase views
A DevOps Code ClearCase® view provides access to resources in DevOps Code ClearCase repositories.
Before you can access resources stored in a DevOps Code ClearCase repository (VOB) or add existing resources to ClearCase source control, you must create a DevOps Code ClearCase view. A ClearCase view selects a specific set of file and directory versions from one or more VOBs so that you can access them on your computer.
Types of ClearCase views
The ClearTeam® Explorer supports the following types of view:
- Dynamic views
- Automatic views
- Snapshot views
- Web views
The dynamic view is the only type of SCM view that is not copy-based. This view type uses the ClearCase multiversion file system (MVFS) to access versions of elements in VOBs over a LAN. Because filesystem access is continuous and in real time, there is no notion of updating a dynamic view: dynamic views are always up to date. To use dynamic views in the ClearTeam Explorer, you must install the ClearCase local (that is, native) client. A dynamic view can support large files that exceed 2 GB. The same is true for a snapshot view.
- Instant workspace creation - Automatic views enable you to start using the workspace immediately, without waiting for it to be populated with any files.
- Per-view VOB mounts - Mounting a VOB in an automatic view immediately makes the version-controlled files in that VOB available in the view. While VOBs mounted for a dynamic view are global mounts that are visible to all dynamic views on that system, VOBs mounted for an automatic view are managed separately for each automatic view. Thus, a set of VOBs mounted in one automatic view can be a different set from those mounted for another automatic view on the same system.
- Shared cache - All of your automatic views on a machine typically share a common cache of version-controlled files: the shared cleartext cache. If one view has fetched a file, all of the other automatic views that were created by the same user on the same machine simply access the cache to obtain that file.
- Prefetching - Although automatic views fetch files when they are first needed (that is, on demand), accessing a file that is already locally cached is orders of magnitude faster than waiting for the file to be fetched from a remote VOB. In addition to the shared cleartext cache, there are a couple of other mechanisms that automatic views use to increase the odds that a file will be cached before you actually need it. One mechanism is load rules, a feature that automatic views share with web and snapshot views. Load rules are not required for automatic views when you work online, but they can improve performance by pre-fetching version-controlled files that you might need. You can also use load rules to fetch the files that you need before disconnecting from the CCRC WAN server.
- "Frozen time" mode - Dynamic views track the changes in VOBs that are made in other views and make them available immediately. In contrast, snapshot and web views make copies of all needed files as of a moment in time (the moment the view is first loaded or at each update operation). Although automatic views can fetch version-controlled files on-demand (when they are first accessed), they "freeze" time when the view is created or updated. If you update an automatic view at 9:00 AM on 16-July but do not access "mycode.c" until 11:00 AM, you'll see the latest version of "mycode.c" as of 9:00 AM, even if someone else checked in a successor version at 10:00 AM from a different view. To show the changes that were made after 9:00 AM 16-July, you would update your view.
- Instant view updates - With snapshot and web views, you must wait until a view update operation completes before using the view. In contrast, you can use an automatic view immediately after starting a view update operation. The view ensures that the correct version of any file is available even if the view update operation has not yet completed.
- Currently, an automatic view does not support large files that exceed 2 GB. The same is true for a web view. If you encounter an error message that ClearCase is unable to get an RPC handle to view errors during checkin, see technote 6474239.
A snapshot view copies files from VOBs (versioned object bases) onto your computer while you are connected to the ClearCase VOB server over a LAN. This type of view is available in the native client only. The files must be explicitly loaded by rules that you specify. As with all copy-based view types, you can work disconnected after you have loaded the files that you need. You must update snapshot views to make sure they contain the versions specified by the stream (in UCM) or config spec (in base ClearCase) if later versions have been checked into the same stream or branch from other views. A snapshot view can support large files that exceed 2 GB. The same is true for a dynamic view.
A web view is a copy-based ClearCase view that is tolerant of high-latency connections to a CCRC WAN server, although it might be used in both wide-area network (WAN) and local area network (LAN) environments. In other respects, web views are similar to snapshot views. Currently, a web view does not support large files that exceed 2 GB. The same is true for an automatic view. If you encounter an error message that ClearCase is unable to get an RPC handle to view errors during checkin, see technote 6474239.
Modifying files in a ClearCase dynamic view
You can modify a file version in a Dynamic view by checking the file out from source control. This marks the element as CHECKEDOUT in the VOB and, if the checkout is reserved (the default setting), guarantees you the right to create the next version of the file. When your modifications are complete, check in the file to commit your changes to the VOB and create a new version that other team members can access.
Modifying files in a ClearCase snapshot view
In a snapshot view, you can load and check out files while connected to a VOB server. You can also make changes to a loaded file without checking it out, a procedure referred to as hijacking. When you reconnect to the VOB server, you can undo the hijacked files or convert them to checked-out files. (When you check in a file that was modified while hijacked, you might be required to merge your changes with those made by users who did not know that you were modifying the file.)
Modifying files in a ClearCase web view
Modifying files in a web view is similar modifying files in a snapshot view, except that CCRC WAN server serves as an intermediary between the web view and the VOB server.
Modifying files in a ClearCase automatic view
Modifying files in an automatic view is similar to modifying files in a web view: you can check out files while you are connected to the CCRC WAN server, or hijack them.