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Subsystem Control Point (SCP) Management Programming Manual

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Subsystem Control Point (SCP) Management Programming Manual—520619-001
B-11
Specifying the Trace-Data Disk File
Algorithm for Computing Trace File Extent Size and Number of
Extents
The trace collector uses this algorithm to calculate an extent size and maximum number
of extents for trace files it creates:
1. Calculate the required number of disk pages.
a. Add 3 pages (for header information) to the number of extended memory
segment pages requested in ZTRC-DDL-TRACE-MODIF.ZXDS-PAGES.
2. Set the test extent size to 2 pages.
3. Calculate the required number of extents based on the test extent size.
a. Divide the number of required pages (from Step 1) by the test extent size to
determine how many extents are needed.
b. If the result is greater than 978 (the file-system limit on number of extents), add
2 pages to the test extent size and return to Step 3.a.
c. If the result from Step 3.a is less than or equal to 978, go to Step 4.
4. Adjust the size and number of extents.
a. If the number of extents calculated in Step 3 is less than 16 (otherwise, skip to
Step 4.b):
1. Set the number of extents to 16 (minimum allowed).
2. Recalculate the extent size by dividing the required pages by 16 and adding
1 to the result. If the result is less than 2, reset it to 2 pages.
3. Allocate the trace-data file with 1 primary extent and 15 secondary extents
of the calculated size. (If the extent size is odd, the system adds 1 page to
make it even.) End.
b. If the number of extents calculated in Step 3 is greater than or equal to 16:
1. Divide the test extent size by the number of extents.
2. If the result is less than 64 (otherwise, skip to Step 4.b.3), add 2 pages to the
test extent size and return to Step 3.
3. If the result from Step 4.b.1 is greater than or equal to 64, add 1 to the
adjusted extent size.
4. Allocate the trace-data file with the calculated number of extents of the
adjusted size. (If the extent size is odd, the system adds 1 page to make it
even.) End.