SCAN—space search method for HDAM and PHDAM
The SCAN keyword is valid with the RELOAD and REORG (Online Reorg function and Reorg function) commands.
You can specify this option in a Reload function global options module or in PLUSIN. The following table describes the keyword.
To do this | Specify this in PLUSIN |
|---|---|
Use bidirected method of the Reload function space search and search backward first. | SCAN(-bbb+fff) |
Use bidirected method of space search and search forward first. | SCAN(+fff-bbb) |
Bypass space search and write the segment to overflow. | SCAN(0) |
Use flip-flop method of space search and search backward first. | SCAN(-+nn) |
Use flip-flop method of space search and search forward first. | SCAN(+-nn) |
Internal default: -10+10 | |
The Reload function allows you to control the placement of all HDAM or PHDAM segments that do not fit in the RAA most favored block, the randomized block. The Reload function can scan the specified number of adjacent blocks for free space before putting the segment into the overflow area.
When you specify SCAN(NO), the Reload function and the IMS techniques of searching for free space are skipped. Any segments unable to fit in the home block are placed in the overflow area.
The number of blocks you specify affects the region size needed to run the Reload function. If the number of blocks is large or the blocks themselves are large, increase the region size by adding the product of the number of blocks scanned, multiplied by the number of bytes per block. If you use the Reload function space search method, you can also control the manner in which the search for space proceeds.
The flip-flop technique (shown in HDAM space search (flip-flop technique)) scans the block immediately behind the prime block, then the block immediately ahead. Next it scans the block two blocks behind, then the block two ahead (and so on), until it finds space or reaches the user-specified number of blocks behind or ahead of the prime block. 'SEARCH n' in a block shows the block is being searched for space to insert the segment.
The bidirected technique (shown in HDAM space search (bidirected technique)) scans a user-specified number of blocks in one direction, then a user-specified number of blocks in the other direction. The starting direction (forward or backward) is also user-specified. 'SEARCH n' in a block indicates the block is being searched for space to insert the segment.
You can set the default value for the SCAN option by using the Reload function ISPF panels or the equivalent batch job. Sample JCL is in member #DBUGLBL of the sample library.
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