VSS_APPLICATION_LEVEL enumeration

The VSS_APPLICATION_LEVEL enumeration indicates the application level, the point in the course of the creation of a shadow copy that a writer is notified of a freeze.

VSS first sends a Freeze event to writers initialized with VSS_APP_FRONT_END (called front-end level applications), then to writers initialized with VSS_APP_BACK_END (called back-end level applications), and finally to writers initialized with VSS_APP_SYSTEM (called system-level applications).

Syntax


typedef enum _VSS_APPLICATION_LEVEL { 
  VSS_APP_UNKNOWN    = 0,
  VSS_APP_SYSTEM     = 1,
  VSS_APP_BACK_END   = 2,
  VSS_APP_FRONT_END  = 3,
  VSS_APP_AUTO       = -1
} VSS_APPLICATION_LEVEL, *PVSS_APPLICATION_LEVEL;

Constants

VSS_APP_UNKNOWN

The level at which this writer's freeze state will occur is not known. This indicates an application error.

VSS_APP_SYSTEM

This writer freeze state will occur at the system application level.

VSS_APP_BACK_END

This writer freeze state will occur at the back-end application level.

VSS_APP_FRONT_END

This writer freeze state will occur at the front-end application level.

VSS_APP_AUTO

This writer freeze state will be determined automatically. This enumeration value is reserved for future use.

Remarks

VSS_APPLICATION_LEVEL is provided to allow application developers to control at what point a writer will receive a Freeze event. This may be important if one writer uses or depends on another writer.

For instance, if an application X is storing data using application Y as an intermediate layer (for example, if Y implements a database used by X), we would describe X as a front-end application, and Y as a back-end application.

In this example, when freezing applications that participate in a shadow copy, you would want X (the front-end application) to suspend its writes to the database prior to freezing Y (the back-end application), the database service itself.

The application level of a writer is set by CVssWriter::Initialize and retrieved by CVssWriter::GetCurrentLevel.

Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

Vss.h

See also

CVssWriter::GetCurrentLevel
CVssWriter::Initialize

 

 

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