Content Snapshots

This Technical Concept is relevant to the following Services: xData, xRoute, xMap, xDima, xCluster and xTour.

Characteristic

Short description

A content snapshot represents a state of dynamically updated Feature Layer content at a specific point in time.

Use

When using dynamically updated Feature Layer data, for example PTV_TrafficIncidents provided by the Content Update Service, there might be scenarios where you want to rely on an earlier version of the data. Such a scenario may be using a high-performance routing A route corresponds to a path of a vehicle through the underlying transport network. The main attributes of a route are the distance and the time that the vehicle travels along the path. network that is calculated on Monday and used for route calculation the rest of the week. Therefore it is possible to save a current state of all automatically updated Feature Layer data for later usage.

Detailed Consideration

Highly dynamic data like PTV_TrafficIncidents Feature Layer are updated consistently and automatically by the PTV xServer. That means a user has no influence on the moment when a module receives a content update. When using partially pre-computed data like high-performance routing networks it is crucial that the same data is referenced for creation as well as for usage of the network. A content snapshot represents such a specific set of data that allows a consistent use of dynamic data together with stateful technologies.

The base path of all content snapshot folders is configured with the parameter core.contentSnapshotPath in the xserver.conf configuration file. The path structure of a content snapshot contains tenant, scope and a unique identifier (UUID).

Management of Content Snapshots

The user data monitor lists content snapshots as well as other user-created data. Furthermore the xdata service provides a management web service A web service represents a communication technology applied in computer networks. It provides an interface described in a machine-processable format, for example WSDL. API similar to the management of high-performance routing networks. These create and delete operations for content snapshots require an activated license key contentSnapshotManagement.

Creation: The operation createContentSnapshot creates a snapshot of the current state of automatically updated Feature Layer data as it is present on the module executing the request.
Listing: All available content snapshots can be listed with listContentSnapshot. The resulting list contains either the list of snapshot ids specified in the ListContentSnapshotsRequest or all available snapshots fitting the user's tenant and scope.
Deletion: User-created snapshots can be deleted using the operation deleteContentSnapshot. If the content snapshot with the specified id is currently in use it is not deleted immediately but marked for deletion, which means that it cannot be used anymore and will be removed later.

Usage of content snapshots with PTV routing and rendering services

Content snapshots are supported by the xRoute, xDima, xData and xMap modules for the following operations:

In order to use the content snapshots with routing and rendering services, an activated license key contentSnapshot is required. The content snapshot identifier has to be explicitely provided in the request (RouteOptions.contentSnapshotId, DistanceMatrixOptions.contentSnapshotId, HighPerformanceRoutingNetworkOptions.contentSnapshotId, MapOptions.contentSnapshotId).

Specifying a content snapshot triggers additional operations to fullfill the request:

Check the validity. In case of an invalid content snapshot due to a deletion or non-existence, the request prematurely fails with an exception.
Load the feature layers and make sure these ones are used in replacement of the current content update.

Moreover, to keep a good trade-off between performances and memory consumption, the last used content snapshot remains loaded. It implies that for several subsequent requests using the same content snapshot, the overhead will be only present on the first request.

For high-performance routing, the content snapshot id is stored in the meta-data and treated as a relevant parameter. This means if the routing type is set to HIGH_PERFORMANCE_ROUTING_WITH_FALLBACK_CONVENTIONAL or HIGH_PERFORMANCE_ROUTING and a content snapshot id is provided in the request, the considered networks are the ones matching exacly this content snapshot id and the other relevant parameters.

Good to know

Dependency on content updates

A content snapshot represents the state of data at a specific point in time. Since the static map data does not change over time, a snapshot contains all the data that is changed by automatic content updates which are usually provided by the PTV Content Update Service. Therefore content updates have to be configured before working with content snapshots.

Deletion of content snapshots

Content snapshots may be related to other user-created data such as High-performance Routing Networks or distance matrices. Be aware of these relations when deleting content snapshots, because a snapshot is only blocked for deletion if it is actually used, directly or indirectly, by a running request. That means if there exists a user-created high-performance routing network that is based on a certain content snapshot, but is not used in any request at the moment, the corresponding content snapshot may be deleted. This would lead to an error when the high-performance routing network is used the next time.

Technical Concept	Feature Layer Basics
Technical Concept	PTV_TrafficIncidents
Technical Concept	Multitenancy
Technical Concept	High-performance routing
Administrator's Guide	Using Content Update Service