tcl.set-ovf-local Verb: Access/TCL


Command tcl.set-ovf-local Verb: Access/TCL
Applicable release versions: AP 6.1
Category TCL (746)
Description sets and displays the local overflow cache size. The presence of a local overflow cache enhances both performance and reliability, and is automatically set up to a reasonable default by the system. Users who wish to further tune their overflow usage may use the "set-ovf-local" command to change this cache to tailor it to specific needs.

When given without any options, the "set-ovf-local" command displays the cache status for the current line. The display shows a 2 by 2 grid of numbers. The explanation for these is as follows:

Legend: (see examples)

"Current" is the current number of frames actually held in a given cache.

"Max" is the maximum number of frames that the cache may hold. Any overflow released to the cache when it has reached its maximum size will be deposited directly into the main overflow table.

"WS" is the row showing the current and maximum workspace cache sizes.

"File" is the row showing the current and maximum file cache sizes.


Besides displaying the current cache status, "set-ovf-local" can be used to modify the current cache maximums by specifying the following numeric parameters on the command line:

ws.max This sets the maximum workspace cache size.

fs.max This sets the maximum filespace cache size.

Cache descriptions:

The workspace cache is a generalized cache used for virtually all memory needs. It is automatically set to a default so that simple TCL commands and FlashBASIC and Pick/BASIC programs will not need to access the global overflow table and can thus avoid the performance cost of doing so. If the user is repeatedly using EXECUTE's of more complex programs, then he/she can try boosting the workspace cache size to see if performance improves.

The file cache is used only when update-protection is active. The update-protection scheme deposits frames into this buffer which it guarentees are syncronized so that no other file or workspace on the disk points to it. This virtually eliminates the posibility of so-called "doubly linked frame" where two files are attached to the same frame after a power outage or crash. This cache is should be large enough to cover the largest group or largest pointer item that is protected by the update protection scheme. For example, if the user has a file with 30K byte items on a 2K frame system, then the file cache should be set to at least 30K/2K = 15 frames.

Cache tuning:

Ideally, a system should be able to operate out of private overflow caches as much as possible. The less the system accesses the global overflow pool, the greater the system performance, and the less chance there is for the overflow to become corrupted in the event of a power outage. To tune the cache sizes, users can try different cache settings, and run the "buffers (s" program to see the change on overflow access. The fields "WS OVF locks" and "FILE OVF locks" show the number of references to the global overflow table per second.
Syntax set-ovf-local {ws.max}{, fs.max} {(options}
Options s supresses the display.

f flushes all caches. All frames held within the current cache are released back to the main table. Note that this operation is automatically invoked when the maximum values are changed. The act of logging off the system will automatically flush all local overflow caches.

g Copies the current maximum cache settings into the global default. Whenever a new user logs in, he/she will automatically aquire this default value. Note that the global defaults are automatically preset to a factory specified value upon reboot, so if a permanent global change is desired, the user should place the "set-ovf-local" command in the system-coldstart macro.
Private Overflow Cache Status:
           Current   Max
WS            2      20
File         10      30

This shows that there are currently 2 workspace frames in the overflow cache 
with a maximum capacity of 20 frames, and 10 file space frames in the overflow 
cache with maximum capacity of 30 frames.

set-ovf-local 100,300 (s

This command will set the maximum workspace cache size for the current line to 
100, and the maximum file space cache size to 300.

set-ovf-local (fs

This command releases all frames in the current overflow cache to the global 

set-ovf-local 100,300 (sg

This command will set the maximum workspace cache size for the current line to 
100, and the maximum file space cache size to 300.  The settings will also be 
copied into the global default area.  All users logging into the system after 
this command has been executed will automatically get caches sized to this 
Related tcl.init-ovf