IBM Mainframe Discussion List <IBM-MAIN@BAMA.UA.EDU> wrote on 03/01/2007 11:16:01 AM:
> From Barry Merrill: > " Writing an SMF record is an SVC call to the SMF address space, with no > physical I/O that has to be managed. Writing to GTF requires the DB2 > Address Space to have to manage each of those tiny chunk writes. I can > see no way in which the overhead to write to GTF would not be > significantly more than sending the > records to SMF. But this is an option based on the way I think it > works, > and is not based on actual measurements. " > > > > Actually I do have a question about this that maybe someone from IBM can > answer: Does the I/O to GTF tapes happen in DB2 or in GTF? How does the > data get from DB2 to the GTF tape? Is Barry correct that the overhead > would be higher to write to GTF vs SMF? When a record is passed to GTF, GTF adds it do a GTFBLOK (whose size is the GTF data set block size) in ESQA. When a GTFBLOK becomes full, an SRB is scheduled to the GTF address space. The SRB routine copies any full GTFBLOKs from ESQA into GTFBUFRs in the GTF address space. The SRB routine the POSTs the writer task in the GTF address space. The writer task uses BSAM to write the GTFBUFRs to the data set. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
