Display Sharing
This section describes
how to optimize RTView Display Server and Display Servlet
performance using Display Sharing.Display Server and Display Servlet performance can be improved by sharing displays among
clients. This is helpful in an environment where many clients typically view
the same display simultaneously.
There are limitations
on the features that can be used on a shared display, so displays to be shared
should be selected carefully.
To configure Display Sharing, you specify the
displays to be shared and the substitutions, if any, to be applied when the
display is opened, in the DISPLAYSERVER.ini
file.
How It Works
Normally, the Display Server loads a copy of a
display for each and every client that requests it. And the Display Servlet
normally then generates the Web page content (for example, HTML, images and
JavaScript)
for each and every client.
When Display Sharing is enabled, the Display
Server instead
loads a single copy of a display for all of the clients to view. The Display Servlet
then generates the Web page content once, stores the content, and reuses that content
for all other client requests for the same display. The Display Servlet keeps
and uses that content until the time interval specified for the SharedDisplayRefreshInterval property in the rtvdisplay.properties
file (located in the servlets\rtvdisplay
directory). By
default, the interval is 15 seconds.
Display Sharing is used only for client requests
that match both the display name and the substitutions, if any, that are listed
in the DISPLAYSERVER.ini
file.
If the Display Servlet
receives a client request for a shared display after the interval has expired,
the Display Servlet checks with the Display Server to see if the stored content is
"stale". That is, if any data has been applied to the display since the
Display Servlet generated the content. If it is not stale the Display Servlet stores the content for
another interval. If it is stale, the Display Servlet gets the updated display from the Display Server and regenerates the content. The Display Servlet purges the stored content for shared displays if it has not been
accessed within one shared display refresh interval, plus one minute.
The maximum number of shared displays for which the Display Servlet stores content is determined by the
MaxSharedDisplays property. By default, the value is 10. Best
practices dictate that the MaxSharedDisplays property be set to a value at least as large as the number of
shared_display entries in DISPLAYSERVER.ini.
The JMX Mbean operation RTViewDisplayServer.Manager.clearDisplayCache can
be used to clear and reload all shared displays in the Display Server, and to clear
all page content for shared displays currently stored in the Display Servlet.
When a client requests a display name that does not
match a shared display and substitution entry in the DISPLAYSERVER.ini
file, the request is processed using the normal process.
Again, the performance benefit of display sharing
is obtained only if multiple clients request the same shared display within a
single shared display retention interval.
Configuring Display Sharing
To configure Display Sharing, add the
name of the display (.rtv) file and the substitutions, if any, to be
applied when the display is opened, to the
DISPLAYSERVER.ini
file.
To configure a shared display, perform
the following steps.
1. Add the
shared_display
property to the DISPLAYSERVER.ini file as follows:
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shared_display <filename> [substitutions]
Where:
<filename>
is the name of a
display (.rtv) file to share.
[substitutions] is an
optional list of substitution string:value pairs, separated by spaces. If a
substitution value contains spaces it must be enclosed in single quotes.
|
|
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For
example:
shared_display navtop.rtv
shared_display summary.rtv $region:East
shared_display summary.rtv $region:West
shared_display summary.rtv $region:'East and West'
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2.
Optionally, add the
SharedDisplayRefreshInterval property
to the rtvdisplay.properties
file (located in the servlets\rtvdisplay
directory). By
default, the interval is 15 seconds. (This step is only required if you
need to change the default setting.) For example:
SharedDisplayRefreshInterval=15
3. Optionally, specify the maximum number of
shared displays for which the Display Servlet stores content by adding the
MaxSharedDisplays
property to the rtvdisplay.properties
file. By default, the value is 10. (This step is only required if you
need to change the default setting.) For example:
MaxSharedDisplays=10
NOTE: Best
practices dictate that the MaxSharedDisplays property be set to a value at least as large as the number of
shared_display entries in the DISPLAYSERVER.ini file.
Monitoring Display
Sharing
To view performance metrics about requests for shared displays
and status information from the Display Servlet, open the servletstatus.jsp
page in a browser:
http://localhost:8068/rtvdisplay/servletstatus.jsp.
The
servletstatus.jsp page contains the
following information:
| Value |
Description |
| Display
Server |
The Display Server hostname and port number. |
| Backup
Server |
The hostname
and port number of the backup Display Server, if one exists. |
| Connection
Pool Size |
The value
of the
DisplayServerConnectionPool property in the
rtvdisplay.properties file. The
DisplayServerConnectionPool property specifies the maximum number
of simultaneous connections the
Display Servlet makes to the Display
Server and, consequently, determines the maximum number of display
requests the Display Server processes simultaneously. |
| Timeout |
The amount of time, in seconds,
for a query to timeout.
|
| Refresh |
The
value of
the
DefaultRefreshInterval property in the rtvdisplay.properties
file. The
DefaultRefreshInterval property specifies
the refresh rate of the Thin Client. |
| Login |
Specifies whether login is enabled. |
| Request Count |
The total number of client display requests received. |
| Connection |
The current connection from the Display Servlet to the Display Server.
|
| Started |
The time that the Display Servlet started. |
| Shared Display
Refresh |
The value of the
SharedDisplayRefreshInterval property, in seconds. |
| Shared
Display Hits/Tries |
The amount of client requests for a page that is satisfied by Display
Sharing, in percent (%). That is, the number of client requests
satisfied by stored content for a shared display divided by the total
number of requests for a display. A high amount indicates that display
sharing is effective, a low amount indicates that it is not effective
for the requests being received.
|
| Shared
Display Updates |
The number of times the Display Servlet has updated
shared display content. |
| Shared
Displays |
The
current number of shared displays divided by the value of the
MaxSharedDisplays
property. This is followed by a scrolled list of the shared displays
currently loaded in the Display Servlet. |
The following is an example of data:
| |
display server: localhost: 3279
backup server: null
connection pool size: 10
timeout: 15 sec
refresh: 15 sec
login: on
request count: 437
connection: localhost:3279
started: 02/04/11 14:14:33.17
shared display refresh:: 15 sec
shared display hits/tries: 222/437 (50%)
shared display updates: 88
shared displays: 3 / 10
blank
nav1
rbt1+$plants:* |
Thin Client
In the Thin Client, you can determine
whether a shared display is being viewed. Right-click in the display and select
Status from the popup menu, then check the Panel ID string shown in the Thin Client Status window. For a
shared display the Panel ID string begins with preload.
Limitations
- The following features should not be used on shared displays,
because these
features can change the state of a display for each user.
| |
- A resizeMode of Layout or Scale.
- Scrolling on the following objects obj_trendgraph02,
obj_bargraph, obj_objectgrid.
- Paging mode on obj_table02.
- User-specific substitutions (for example, $rtvuser).
- Role-specific substitutions (for example, $rtvrole).
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- The substitutions in a client request for a shared display must exactly match
those specified in the entry in DISPLAYSERVER.ini, including the order of the
substitutions, otherwise the request is processed as a non-shared
display.
- All shared displays share the same set of global variables and functions.
Therefore, if a user changes the value of a shared display global variable,
all users viewing any shared display will see that value
change--including users on separate machines. Whereas, for
all non-shared displays, the Display Server uses a separate set of global
variables that it maintains for each browser session. Therefore, if a user
changes the value of a global variable no other non-shared displays are affected.
- A drilldown to a shared display behaves as
though the Remove Existing
Substitutions box was checked in the Drill Down Properties dialog. This is
necessary so that substitutions in the source display are not included in the
drilldown substitutions, which might prevent them from matching the shared
display substitutions.
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