Cumulative RDW's+4 (first beginners error). Kees.
-----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Reichman Joseph Sent: 19 July, 2016 16:33 To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Bsam VS Qsam for VB records As Far as I can see all the I/O we do here is qsam There was an issue here as Jay Campbell pointed out where writing a VB record had a valid RDW but the BDW was zeros. Using qsam I would have no idea what the BDW was as the system takes care of that. I am assuming if you use BSAM you decide the number of records that make up a block and each record is proceeded by a RDW and the block which you write has cumulative BDW. Am I on the right track ? Joe Reichman Joe Reichman IT Specialist Master Files Division New Carrollton Federal Building, B7-182 OS:CTO:AD:CP:I:IB Flex M,T,Th,F Home office (240) 863 - 3965 Office (240) 613-4350 Cell (917) 748-9693 TOD M - F 7:30 am - 4:00 pm -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@listserv.ua.edu] On Behalf Of John McKown Sent: Tuesday, July 19, 2016 10:24 AM To: IBM-MAIN@listserv.ua.edu Subject: Re: Bsam VS Qsam for VB records On Tue, Jul 19, 2016 at 9:02 AM, Reichman Joseph <joseph.reich...@irs.gov> wrote: > Hi, > > Would anyone know the plus and or minus for using BSAM as opposed to > QSAM for VB records. It seems with BSAM there is more control e.g. > specifying the BDW as well as the RDW. Wondering about performance. > > I am guessing if you know what you are doing BSAM would be faster. If > anyone could point me to examples using BSAM would appreciated. As I > have mainly used QSAM specifying the RDW > > Thanks > > Joe Reichman > In general (VB or FB), QSAM is much easier to program. The access method just hands you individual records. But you pay for this in that you cannot do I/O overlap yourself. With BSAM, you do a READ. But the _block_ is not available to you (for certain sure) until you do a CHECK. But this allows you to test the I/O ECB and "do something else" if it has not been POST'd yet. A type of "useful polling" loop. Also, if you are reading multiple files, you can do a ECBLIST and wait for any one of the I/Os to complete instead of doing the I/O serially. Again performance. The problem is that _your code_ must de-block the individual records. For VB, you should probably determine the number of byte read in the block (they aren't necessarily all the same size, you know) and check that the value in the BDW agrees with this number. And the code to do this is non-obvious because what you end up doing is knowing how many bytes you asked for and the I/O control block tells you the residual byte count - not the byte read but more like "you asked to read some bytes and there were were not enough in the block - the block was short by ? bytes). So the number of bytes read is the number of bytes you requested in the READ (not given back to you - you must remember) minus the "residual byte" count which is returned. IOW - unless you are very clever and you have a real need for I/O overlap performance, and you don't mind the maintenance programmer cussing you out, then I'd just go with QSAM. -- "Worry was nothing more than paying interest on a loan that a man may never borrow" From: "Quest for the White Wind" by Alan Black Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ******************************************************** For information, services and offers, please visit our web site: http://www.klm.com. This e-mail and any attachment may contain confidential and privileged material intended for the addressee only. If you are not the addressee, you are notified that no part of the e-mail or any attachment may be disclosed, copied or distributed, and that any other action related to this e-mail or attachment is strictly prohibited, and may be unlawful. If you have received this e-mail by error, please notify the sender immediately by return e-mail, and delete this message. Koninklijke Luchtvaart Maatschappij NV (KLM), its subsidiaries and/or its employees shall not be liable for the incorrect or incomplete transmission of this e-mail or any attachments, nor responsible for any delay in receipt. Koninklijke Luchtvaart Maatschappij N.V. (also known as KLM Royal Dutch Airlines) is registered in Amstelveen, The Netherlands, with registered number 33014286 ******************************************************** ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
