This document describes the prerequistes, process, control and start of a dynamic swap pool reorganization.
The following topics are covered:
Dynamic swap pool reorganization is only possible when the physical swap pool contains only one logical swap pool. In this case, the swap pool slots are all of the same size. If necessary, the number of logical swap pools and the slot sizes can be adjusted to meet the requirements. Slot sizes are adjusted by reorganizing the swap pool dynamically.
The statistical area of the swap pool directory contains two statistics tables which are used for swap pool reorganization:
swap-pool-reorganization plus table
swap-pool-reorganization minus table
The swap-pool-reorganization plus table contains information on the Natural user areas which could not be placed into the swap pool because their compressed length exceeded the swap-pool slot size.
The table contains 11 entries:
The first 9 entries count the number of user areas whose length exceeded the slot size by 1 to 9 units.
The 10th entry counts the number of user areas whose length exceeded the slot size by more than 9 units.
The 11th entry contains the average length of those user areas counted by the 10th entry.
The swap-pool-reorganization minus table contains information on the Natural user areas whose compressed length was smaller than the swap-pool slot size.
The table contains 11 entries:
The first 9 entries count the number of user areas whose length was smaller than the slot size by 1 to 9 "units".
The 10th entry counts the number of user areas whose length was smaller than the slot size by more than 9 units.
The 11th entry contains the average length of those user areas counted by the 10th entry.
The size of a "unit" is defined with the keyword parameter
SWPFACT.
Dynamic swap-pool reorganization is controlled via the following keyword
parameters in the macro
NTSWPRM.
| Parameter | Specifies |
|---|---|
SWPSLSZ
|
the slot size for the first initialization of the swap pool. The default size is 62 KB. |
SWPTFIX
|
if the slot size is to be fixed or dynamic. With fixed slot size, there is no dynamic swap pool reorganization. If the slot size is defined as not fixed, the swap pool is dynamically reorganized when necessary (this is the default). |
SWPTIM1
|
the time interval at which a check is to be performed to ascertain whether a swap pool reorganization is necessary. By default, the check is performed every 30 minutes. |
SWPTIM2
|
the time to elapse after the check for the necessity of a swap pool reorganization is performed and before the reorganization is to be started. By default, a reorganization is started 2 minutes after a check has proved a reorganization to be necessary. |
SWPUSER
|
the rate of compressed user threads (in percent) which are too long for the actual SWP slot length. If this value is reached and the physical SWP contains only one logical swap pool, an SWP reorganization will be announced. |
SWPFACT
|
the factor for a "unit" in the swap pool reorganization plus table and minus table. |
There is no need to change the default values for any of these parameters (unless you feel that slot size optimization is not performed efficiently enough).
For testing and optimizing, you can dynamically change the values for
these parameters online using the Natural Swap Pool Manager, which is part of
the Natural utility SYSTP.
The check is based on:
the overall number of dialog steps during the time between two checks;
the percentage defined with the
SWPUSER
parameter;
the maximum number of logical swap pools defined with the
SWPLSWP
parameter;
the minimum difference of slot sizes for different logical swap pools;
the values of the swap-pool reorganization plus and minus tables
(these tables are influenced by the setting of the
SWPFACT
parameter);
the total size of the physical swap pool.
The number of necessary logical swap pools with the corresponding slot
sizes will be computed if the number of user areas whose compressed length was
greater or smaller (by at least one unit) than the current slot size is more
than n percent of the number of dialog steps
(n being the value of the
SWPUSER
parameter).
When the swap pool is reorganized, the new logical swap pools are used. If the physical swap pool contains more than one logical swap pool after the reorganization, there will be no further dynamic swap-pool reorganization.
Natural will only check whether the swap pool needs to be reorganized if the physical swap pool contains no more than one logical swap pool.
Once the time specified with the
SWPTIM1
parameter has elapsed, a check is performed to determine whether a swap-pool
reorganization is necessary.
If swap-pool reorganization is not necessary, the timer set with the
SWPTIM1 parameter (time interval between checks) is
activated again.
If swap-pool reorganization is found necessary, the timer set with the
SWPTIM2
parameter (time interval between end of check and start of reorganization) is
activated: no further user areas can be placed in the swap pool; user areas
held in the swap pool can still be used and read into the user thread. Once
this second time interval has elapsed, swap-pool reorganization is started.
After the time specified with the
SWPTIM2
parameter has elapsed, the swap pool is reorganized while the current online
session continues:
The compressed user areas which are still held in the swap pool are written to the swap file (or roll facility under CICS).
The contents of the swap-pool-reorganization statistics tables are
written to SYSLST and then deleted from the tables.
The swap-pool is re-initialized with the newly computed values.
The timer set with the
SWPTIM1
parameter (time interval between checks) is activated again.
The Natural swap-pool manager, which is part of the Natural utility
SYSTP (see the
Natural Utilities
documentation), can be used to obtain information on swap pool statistical
data, sizes of Natural buffers and user threads.
