Varnish Enterprise

MSE4 control (mse4)


The mse4 vmod enables controlling certain aspects of how Varnish and MSE4 handles objects through VCL, as well as querying MSE4 specific information about the objects.

The mse4 vmod can only be loaded if the Varnish instance is configured to use MSE4. If the Varnish instance is not configured to MSE4, the VMOD will cause the VCL initialization to fail.

In advanced configurations this vmod will be used to assign a category to objects as they are inserted into the cache. Please see :ref:mse4-categories(7) for more information about categories and how to configure them.



BOOL set_category(STRING category)

Set the content category to use when creating new objects. The category specified needs to be a leaf node defined in the categories section of the MSE4 configuration file.

It is only valid to call this function from VCL backend context. Calling it from any other VCL functions will cause a transaction failure.

The return value is true if a category is successfully associated with the current fetch.


  • category accepts type STRING

Type: Function

Returns: Bool

Restricted to: backend


VOID set_storage(ENUM {EPHEMERAL, PERSISTED} storage)

Set the preferred storage mode for newly created objects.

EPHEMERAL directs Varnish to create objects that are only kept in memory. The objects will be lost if the Varnish daemon is restarted.

PERSISTED directs Varnish to create objects that are persisted to disk if possible. This allows the memory held by the object to be reclaimed when necessary, and then later read the data back from disk when needed. When a persisted object can not be created (for example if the selected category does not have any stores configured), an ephemeral object is created.

The default storage mode is PERSISTED.


  • storage is an ENUM that accepts values of EPHEMERAL, and PERSISTED

Type: Function

Returns: None

Restricted to: backend


STRING get_location(ENUM {STORE, BOOK} type)

Returns the identifier of the MSE4 store or book the current object is being held in. Can only be called from vcl_hit and vcl_deliver. Will return none if object is stored in memory only MSE4 or NULL if it is not currently being stored in MSE4. Storage name can also be obtained using .storage on the object.


  • type is an ENUM that accepts values of STORE, and BOOK

Type: Function

Returns: String

Restricted to: vcl_hit, vcl_deliver


The mse4 VMOD is available in Varnish Enterprise version 6.0.13r2 and later.