> When I do a qsam get the physical I/O is for 1 block every get just ups a > pointer
No. When you do a GET, QSAM not only returns a logical record, it also does whatever housekeeping is necessary. That includes scheduling the I/O for subsequent blocks if necessary. Further, the number of CCWs is not the same as the number of physical blocks. Further, the channel program may include CCWs for multiple physical blocks. The scheduling for QSAM is the same as the scheduling for BSAM. The advantage of QSAM is that it requires less programming, at the expense of not supporting FIND, NOTE, POINT or STOW. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List [[email protected]] on behalf of Joseph Reichman [[email protected]] Sent: Sunday, March 21, 2021 10:21 AM To: [email protected] Subject: Re: Overlapped I/O completion I don’t understand what the statement “QSAM does overlapped I/O automatically” When I do a qsam get the physical I/O is for 1 block every get just ups a pointer BSAM allows me to do multiple Reads each with their own DECB So I already initiate lots of physical I/O mainly because I have lots of records or blocks I find it hard to believe that a qsam get does anything more than read 1 block ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
