SERVGA parameter
Above the bar server areas
Summary
- Default value
- 0
- Parameter type
- System
- Where set
- On User 0's parameter line
- Related products
- All
- Introduced
- Model 204 V7.5
Description
The SERVGA parameter controls which server tables are allocated in the ATB-swappable-server area.
Only NTBL and QTBL can be placed above-the-bar in a swappable area.
Each server table to be allocated in that area is controlled by a bit in SERVGA; if the bit is on, the corresponding server table is allocated in the ATB-swappable-server area.
The bits are:
| Bit | Server table placed above the bar | Required version of Model 204 |
|---|---|---|
X'00004000' | NTBL | 7.5 or later |
X'00002000' | QTBL | 7.5 or later |
Note: The bits corresponding to NTBL and QTBL can also be set in SERVNSA but should not be set in both SERVGA and SERVNSA — if they are, an error message is issued and the Online fails to come up.
SERVGSZ is the amount of space in bytes required for the swappable above-the-bar server tables per server. The total amount of storage allocated for swappable above-the-bar server areas equals SERVGSZ rounded to 4K and multiplied by NSERVS. When sizing SERVGSZ, it should accomodate the largest swappable above-the-bar table sizes that might be needed.
Some server tables can alternatively be placed above-the-bar in a non-swappable area. This can be indicated with the SERVNSA and SERVNSSZ parameters.
While it might seem odd to have above-the-bar swappable server areas, especially if swapping to above-the-bar memory, placing NTBL and QTBL in a swappable area can save quite a bit of real memory. This is especially true if the RESPAGE parameter is set to a non-zero value and there are significantly more users (NUSERS) than servers (NSERVS). In such a case, most swapped out users would either be using a resident (shared) NTBL and QTBL, or they would be logged out and only using a single 4K page. As such, reserving the amount of space required for NTBL and QTBL (which can typically get quite large) in the non-swappable above-the-bar area for all the swapped out users can waste a significant amount of real storage.