Databases Reference
In-Depth Information
Snapshot
A
Snapshot
is a query result set created by a
ViewSet
. When a report is first
rendered, a
ViewSet
is opened to generate the initial result, which is called
a Snapshot. The XML representation of the Snapshot is then transformed to
DHTML using View-specific XSL, and sent to the client along with JavaScript.
Snapshots are cached in the BAM Server. So, every time the same report is
opened in another browser session, the Snapshot will be retrieved, and sent
back to the client without generating from scratch, which helps improve the re-
port rendering performance.
Snapshots can be used to generate static Views. To produce dynamic Views, or
in other words, to render a report that can reflect the data changes in real time,
you will need a push-based mechanism called Active Data, which we will look at
next.
Active Data
Active Data
is the continuous stream of changes that the
ViewSet
can pro-
duce. Once a report is first rendered with a Snapshot, any subsequent changes
to the Snapshot of the ViewSet will be captured at the server side, and pushed
back to the client. This is what we call a
push-based mechanism.
A push-based mechanism is an efficient way of delivering real-time notifications
to the client. Unlike the polling approach, in which clients need to consistently
send requests to the server, Active Data allows the server to send the changed
data in an incremental way, instead of transferring all the report data to the client,
and thus can provide significant advantages, such as the following:
•
Leveraging client and server resources more efficiently
•
Significantly reducing the network traffic
•
Fast rendering report with Active Data
