Introduction

The goal of 'smart viewchache cleaning' (svcs) is to provide flexibility in the cache system when cleaning the viewcache of an objects nodes. It is aimed to extend default behaviour when cleaning cache in specific(site-depended) situations.

If 'svcs' is turned off (default) the caches of all nodes on the system will be cleared if a published object is changed.

Smart viewcache cleaning is available from eZ publish 3.4.2.

Concepts

When the content of an object is changed the cache of its nodes should be cleared. To determine for which nodes eZPublish should clear the caches, the 'smart viewcache cleaning system'(svcs) is used.

The default behaviour of 'svcs' when an object is changed is to clear the caches of:
- all published nodes of the object
- parent nodes
- nodes of reverse related objects

From 3.5 it will also clear the caches of:
- nodes of objects with the same keywords (if the object has one or more ezkeyword attributes)

The 'extended' behaviour of 'svcs' is served to determine additional node's identifiers. It depends on settings in ini-file and based on 'path_string' attributes of the published nodes.

Thus the input parameter of 'svcs' is the object's identifier and the output is a list of node's identifiers for which cache should be cleared.

Settings description

Settings are applied to 'extended' behaviour only and can be found in
'viewcache.ini' file in your settings directory.
The ini-file consists of several sections: one common section and sections which describes rules to calculate additional node's indentifiers.

The common section is named 'ViewCacheSettings' and has these options:

   Name                       Value              Description

   --------------------------------------------------------------------------

   SmartCacheClear            enabled,           enables/disables 'svcs'.

                               disabled(default)  If disabled then caches for

                                                   all nodes will be cleared;

Other sections should begin with indentifier of the class for which rule is made.
Allowed options for these sections are:

   Name                       Value              Description

   --------------------------------------------------------------------------

   DependentClassIdentifier   forum, folder,     identifier of the class.

                               article, etc.      Caches of the nodes of

                                                   objects of this class will

                                                   be cleared if the object

                                                   for which cache is cleaning

                                                   now belongs to the class

                                                   which identifier is pointed

                                                   as name of this section;

                                                   this is an array so multiple

                                                   identifiers can be used;

 

   ClearCacheMethod           see below          for which nodes cache

                                                   should be cleared(parent,

                                                   reverse related, etc.);

 

   ObjectFilter               list of object's   if specified then caches of

                               ids                these objects only will

                                                   be cleared. Means

                                                   'all objects of this class'

                                                   if not specified;

 

   MaxParents                 integer(1,...)     Specifies the maximum

                                                   parents to check in

                                                   node's 'path_string'.

                                                   Means 'unlimited' if not

                                                   specified;

'ClearCacheMethod' values:

   Name                                           Description

   --------------------------------------------------------------------------

   clear_object_caches_only                        clear cache for object's

                                                   nodes only;

 

   clear_object_and_parent_nodes_caches           clear cache for object's

                                                   nodes and their parent;

 

   clear_object_and_relating_objects_caches       clear cache for object's

                                                   nodes and reverse related

                                                   objects;

 

   clear_parent_nodes_caches_only                 clear cache for parent

                                                   nodes;

 

   clear_parent_nodes_and_relating_caches         clear cache for parent

                                                   nodes and reverse related

                                                   objects;

 

   clear_relating_caches_only                     clear cache for reverse

                                                   related objects;

 

   clear_keyword_caches_only                      clear cache for objects with

                                                   the same keywords (from 3.5);

 

   clear_all_caches                               clear cache for object's

                                                   nodes, their parent,

                                                   reverse related objects and

                                                   (from 3.5)

                                                   objects with the same keywords;

Examples

Assume that we have a content structure like this:

eZPublish(nodeID = 2, class_identifier = folder)

|

|-- Forum folder(nodeID = 58, class_identifier = folder)

   |

   |-- Interesting forum(nodeID = 59, class_identifier = forum)

       |

       |-- Topic 1(nodeID = 60, class_identifier = forum_topic)

       |  |

       |  |-- Reply1(nodeID = 62, class_identifier = forum_reply)

       |  |

       |  |-- Reply2(nodeID = 126, class_identifier = forum_reply)

       |  |

       |  | -- Reply3(nodeID = 127, class_identifier = forum_reply)

       |

       |-- Topic 2(nodeID = 61, class_identifier = forum_topic)

Users can add replies to the 'Topic 1'.

By default when 'SmartCacheClear' is enabled and user adds new reply to the
'Topic 1' viewcache of this reply and its parent('Topic 1') will be cleared.
Looks fine.

Case 1

Assume now that we need to display forum name and number of post in this
forum when viewing 'Forum folder'. By default after adding new reply cache of
'Forum folder' will not be cleared and viewing of 'Forum folder' will display
outdate information. To fix this you can use 'extended' behaviour of 'svcs'.
You need to make a rule: if new 'forum_reply' was added(published) to 'forum'
then clear cache of the parent of the 'forum'. Thus next lines should be added
to 'viewcache.ini' file:

[forum_reply]

DependentClassIdentifier[]

DependentClassIdentifier[]=forum

ClearCacheMethod=clear_parent_nodes_caches_only

So now when new 'forum_reply' object will be published 'svcs' will look to
ini-file, find [forum_reply] section and start to search objects of 'forum'
class in 'path_string' attribute of 'forum_reply' node.

For example, if you'll add 'Reply3' object its node will have 'path_string'
attribute: '/1/2/58/59/60/127'. Using last value in path 'svcs' will
determine class identifier of 'Reply3' and thus will find right section in
ini-file. Then 'svcs' will search for nodes which class identifier is equal
to one of the values in the 'DependentClassIdentifier' variable. Searching of appropriate
nodes occures in reverse order: node with id=60 will be checked first, then
node with id=59, ..., id=2. Node with id=60 does'n belong to 'forum' class,
so its cache will be untouched. Next node has id=59 and it belongs to
'forum' class, so its cache will be cleared. Residuary nodes in the path(58,
2) doesn't belongs to 'forum' class, so their cache will be untouched.

Case 2

Assumes now that in addition to 'Case 1' we have a folder named 'Common folder'
which is published under 'eZPublish' folder and contains 'Forum folder' as
related object. Since 'Forum folder' cache is cleared when new 'forum_reply'
is published cache of 'Common folder' has to be cleared too. For this purpose
we need to add another rule to ini-file:

[forum]

DependentClassIdentifier[]

DependentClassIdentifier[]=folder

ClearCacheMethod=clear_relating_caches_only

MaxParents=1;

Now when new 'forum_reply' object will be created cache of 'Forum folder' will be cleared because of rule for 'forum_reply' class and cache of 'Common folder' will be cleared too because of rule for 'forum' class.
Since the 'path_string' of new reply looks like '/1/2/58/59/60/...', there are two 'folder' nodes in the path: with id=2 and id=58. But we don't need to clear cache for 'eZPublish' folder (nodeID=2). 'MaxParents' variable was used to fix this. In this exapmle it says: don't search 'folder' objects that are more then '1' node away from 'forum' node.

Actually for the 'case 2' we can remove 'rule 1' and 'rule 2' and replace them with rule:

[forum_reply]

DependentClassIdentifier[]

DependentClassIdentifier[]=folder

ClearCacheMethod=clear_object_and_relating_objects_caches

MaxParents=3;

#If 'Forum folder' has object_id=56 for example then the rule above can be more hard by adding next lines:

ObjectFilter[]

ObjectFilter[]=56

The lines above restrict the rule to one 'folder' object which has
object_id=56.