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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 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.
Arguments:
category accepts type STRINGType: 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.
Arguments:
storage is an ENUM that accepts values of EPHEMERAL, and PERSISTEDType: 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.
Arguments:
type is an ENUM that accepts values of STORE, and BOOKType: Function
Returns: String
Restricted to: vcl_hit, vcl_deliver
BOOL is_mse4()
This function returns true if the Varnish server is configured to use the MSE version 4 stevedore. This can be useful in order to construct alternate VCL instructions depending on the storage configuration of the Varnish server instance.
Arguments: None
Type: Function
Returns: Bool
The mse4 VMOD is available in Varnish Enterprise version 6.0.13r2
and later.