Microsoft Office Tutorials and References
In Depth Information
Understanding Operational Concepts
in a separate session being opened. For example, if a user opens a Web Part Page with three EWA instances,
two of them opening workbook A and the third opening workbook B, then three sessions will be opened.
When the same user or a different user opens the same Web Part Page in a new browser instance, three
more sessions will be opened.
Sessions provide isolation for the user. Changes performed in one session are not seen by any other
session. For example, if two sessions are opened with the same workbook, and the user changes some
workbook cell values in the first session, the user of the second session (be it the same user or a
different one) will not see those changes in the second session. The best way to think of a session on the server
is to imagine users opening workbooks in read-only mode in Excel. Each of those instances of Excel is a
session, and changes made in those sessions are kept within them until they are saved.
The session is closed when the workbook is closed, either explicitly through the API or when a new
workbook is opened in the EWA (depending on the EWA settings). In addition, sessions are automatically closed
when a configurable timeout has expired after a period of user inactivity. After a session times out, the
workbook continues to be displayed in the EWA, and the user is notified if he or she makes changes to
the timed-out session that will be lost. A new session is then opened.
Session Settings
Each session consumes server resources, mainly memory and (when a request is being performed)
additional resources such as a CPU and I/O. Administrators should configure the server for the right balance
between preserving these resources and providing adequate service to their users.
Administrators can configure the maximum number of sessions a user is allowed to open at any time. By
default, this is set to 25 sessions.
In addition, administrators can configure the session timeouts. There are two settings for timeouts. The
short session timeout is used when the session has a workbook that was just opened (with no other
operation performed on the workbook), and has a default value of 75 seconds. The session timeout is used after
additional interactivity has been performed on the workbook, and has a default value of 5 minutes. In
many cases, dashboards just display (open) workbooks without any additional interactivity, so setting a
shorter timeout helps preserve server resources. You can change these timeout settings at the trusted
location level. For more information about settings and trusted locations granularity, see Chapter 7.
Exposing the Session ID
The web service API exposes the session ID. It returns the session ID when a workbook is opened, and
the session ID is passed as a parameter to the other API methods.
The EWA also exposes a JavaScript method that can be called to get the session ID from a running instance
of the Web Part. You can extend the EWA to other controls on a page that interacts with its session through
the API.
Session State
After each operation is finished, the session is left in a certain state. Operations on the session can change
its state or query its state. Closing the workbook is a special operation that terminates the session.
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