Certain attributes associated with GLOP data determine modification properties and how the GLOP set maps the GLOP data.
GLOP Modification Attributes
GLOP modification attributes determine whether the GLOP is read-only, read/write, globally modifiable, or disabled.
| Attribute | Description |
|---|---|
| Read-Only | Used for GLOP data that never changes. The memory access is actually set to read-only. Any attempt to change the GLOP data causes a system reset when running in unprotected mode or a segmentation violation error result when running in protected or secure mode. |
| Read/Write | Used for GLOP data that changes at run time. The memory can be read and written at any time. However, to prevent simultaneous updates from conflicting with each other for different external routines that might have the same GLOP data mapped, the best practice is to apply a write lock on the GLOP data by the writer and a read lock by the readers. |
| Globally Modifiable | Used for GLOP data that might be globally modified at run time. It is read/write GLOP data that can be changed on all vprocs on all nodes at once. If this mode is not set, the GLOP data cannot be updated in a global manner. |
| Disabled | Used for GLOP data that is not to be mapped. There is a definition for it in one or more sets but the access to it has been turned off. |
You set the modification attributes for GLOP data when you call the DBCExtension.GLOP_Add stored procedure to add GLOP data and GLOP mappings to a GLOP set. For details, see DBCExtension.GLOP_Add Stored Procedure.
GLOP Mapping Attributes
GLOP mapping attributes determine how a GLOP set maps GLOP data.
| Attribute | Description |
|---|---|
| Normal | Normal mapping mode means the GLOP data is mapped as indicated by the GLOP type specifications. |
| Shared | Shared mapping mode overrides the normal GLOP data mapping and maps one shared copy of the GLOP data per vproc no matter what type it is. The mapping mode attribute is associated with a GLOP set. If several GLOP sets have the shared flag set for the same GLOP data, they get the same logical address to the GLOP data. If an additional set for the same GLOP data has the normal mode set, it gets a separate copy of GLOP data independent of the other shared one. This setting is not relevant for read-only GLOP data because only one copy is ever mapped per node.
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You set the mapping attributes for GLOP data when you call the DBCExtension.GLOP_Add stored procedure to add GLOP data and GLOP mappings to a GLOP set. For details, see DBCExtension.GLOP_Add Stored Procedure.
GLOP Data Ageing
Read-only GLOP data can be aged out of memory. The ageing timeout can be specified in the number of minutes of inactivity. This provides a way to reduce the use of memory and disk resources for unused GLOP mappings.
Read/write or globally modifiable GLOP data does not age out.
GLOP data that is session based is deleted when the session logs out, GLOP data that is transaction based is deleted when the transaction terminates, and GLOP data that is request based is deleted when the request ends.