When creating overlays in SIS using spatial data held in Oracle users should ensure that the map window view extents in SIS are set to a scale of approximately 1:5000 (or less) and be focused on an area which is coincidental with the spatial data. The following table lists what might happen if the view extents are incorrectly set and data is requested from the Oracle database:
|
Overlay Mode |
Incorrect focus of |
Scale too high in Map window |
| Dynamic | No data displayed | Data will be drawn slowly. Resources on the server will be used. Network traffic will increase. |
| Cached (with spatial extents) |
No data displayed | Data will be drawn slowly. Additional resources on the server will be used. Network traffic will increase. Client machine may run out of memory causing the client to 'lock up'. |
| One off import (with spatial extents) |
No data displayed | Data will be drawn slowly. Additional resources on the server will be used. Network traffic will increase. Client machine may run out of memory causing the client to 'lock up'. |
Care needs to be taken when using the select all features operation whilst an Oracle overlay is hittable. The table below lists the affects of selecting all features on Oracle overlays in different modes:
| Overlay Mode |
Select All/F7/Overlay/Select items |
| Dynamic |
SIS will count all the features that exist in the overlay's underlying Oracle table. There may be many more features in the table than displayed in SIS so the operation may take a long time. |
| Cached (with spatial extents) | SIS will count all the features that exist in the cached overlay only. |
| One off import (with spatial extents) | SIS will count all the features that exist in the one off import overlay only. |
Oracle recommend the use of Oracle specific firewalls when placing an Oracle server behind a firewall.
Standard firewalls cannot cope with Oracle’s communication mechanism between a client and a server. Client information is sent on a given port (usually 1521) but return communication may use a random port. From the user’s point of view it appears as if the client cannot communicate with the server.
For further information contact Oracle.
Note: PostGIS only requires Port 5432 to be opened in a firewall.
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