Subsystem Control Point (SCP) Management Programming Manual

Tr ac ing
Subsystem Control Point (SCP) Management Programming Manual—520619-001
B-6
Tracing to Disk
Tracing to Disk
If ZTRC-DDL-TRACE-MODIF.ZCOLL has a value of ZSPI-VAL-TRUE or is blank,
the collector actively monitors the extended segment and write blocks of trace records to
the disk file as they become available.
When tracing to disk, the collector process reads and writes a block of trace records
from the segment, as Figure B-3
shows.
Sometimes the tracing process writes trace records to the extended data segment more
quickly than the collector can write the records to the disk file. Figure B-4
shows a
tracing process about to overtake the collector. The data it is writing has wrapped around
the segment (always allowed for traces to disk) and is about to overwrite records not yet
written to disk by the collector. In response, the tracing procedure stops writing trace
data to the extended segment until the collector process has copied the threatened trace
records to disk.
Figure B-3. A Collector Process Reads and Writes Records
Extended Data Segment
VST039.vsd
Block Written
to Disk by
Collector
Last Record
Written by
Tracing Process
Trace-Data Disk File