BUFNO question 
Author Message
 BUFNO question

In any given MVS or zOS installation, for simple QSAM file
processing, is there a default for the BUFNO if I do
not specify it on the DCB stmt in the JCL?

For sake of argument, you may also assume that I will
be using MACRF=(GL or PL) on the DCB in the program.

If site-dependent, how would I tell what that value is ?

If I code it on the DCB in the program, will it override
what's on the DCB in the JCL if coded ?

Any thoughts or ideas will be appreciated.

Thanks



Sat, 28 Jan 2006 09:34:59 GMT  
 BUFNO question
SR

I believe the default for QSAM is 2 buffers in order to support overlapped
I/O while minimizing memory usage.

It's a game of dimenishing returns usually after the 2nd buffer in most
cases.  However, if the blocksize is small, there can be significant gains
by specifying a higher number in DCB or JCL to override default.  I believe
there is also an option to specify chained channel commands which also
helped speed up transfer for small blocks by allowing channel to chain next
block in time to no miss next rotational position sensing interrupt for next
block on disk devices.


Quote:
> In any given MVS or zOS installation, for simple QSAM file
> processing, is there a default for the BUFNO if I do
> not specify it on the DCB stmt in the JCL?

> For sake of argument, you may also assume that I will
> be using MACRF=(GL or PL) on the DCB in the program.

> If site-dependent, how would I tell what that value is ?

> If I code it on the DCB in the program, will it override
> what's on the DCB in the JCL if coded ?

> Any thoughts or ideas will be appreciated.

> Thanks



Sat, 28 Jan 2006 16:56:26 GMT  
 BUFNO question
On Tue, 12 Aug 2003 04:56:26 -0400, "Don Higgins"

Quote:

>SR

>I believe the default for QSAM is 2 buffers in order to support overlapped
>I/O while minimizing memory usage.

>It's a game of dimenishing returns usually after the 2nd buffer in most
>cases.  However, if the blocksize is small, there can be significant gains
>by specifying a higher number in DCB or JCL to override default.  I believe
>there is also an option to specify chained channel commands which also
>helped speed up transfer for small blocks by allowing channel to chain next
>block in time to no miss next rotational position sensing interrupt for next
>block on disk devices.

<snip>
And I remember the time some COBOL programmer specified 100 alternate
read areas for card input.  Or was it 1000.  Long time back.   This
was on a system with HASP.

Crashed the system, I think.  The program, certainly.  Trying to
allocate that much memory, or else HASP got sick trying to handle it.
Can't remember just which.

With HASP, no alternate areas should be needed for cards or printers.

--
Arargh308 at [drop the 'http://www.' from ->] http://www.arargh.com
BCET Basic Compiler Page: http://www.arargh.com/basic/index.html

To reply by email, remove the garbage from the reply address.



Sat, 28 Jan 2006 17:34:16 GMT  
 BUFNO question

:>In any given MVS or zOS installation, for simple QSAM file
:>processing, is there a default for the BUFNO if I do
:>not specify it on the DCB stmt in the JCL?

I believe that it is five nowadays.

:>For sake of argument, you may also assume that I will
:>be using MACRF=(GL or PL) on the DCB in the program.

:>If site-dependent, how would I tell what that value is ?

:>If I code it on the DCB in the program, will it override
:>what's on the DCB in the JCL if coded ?

Yes.

DCB in program is primary.

Then JCL.

--

http://www.dissensoftware.com

Director, Dissen Software, Bar & Grill - Israel



Sat, 28 Jan 2006 17:45:25 GMT  
 BUFNO question

Quote:

>In any given MVS or zOS installation, for simple QSAM file
>processing, is there a default for the BUFNO if I do
>not specify it on the DCB stmt in the JCL?

>For sake of argument, you may also assume that I will
>be using MACRF=(GL or PL) on the DCB in the program.

>If site-dependent, how would I tell what that value is ?

>If I code it on the DCB in the program, will it override
>what's on the DCB in the JCL if coded ?

>Any thoughts or ideas will be appreciated.

>Thanks

If I recall correctly it is 3 to 5.  The shops that I am aware of use
100K / divided by the actual file blocksize.
I'm sorry, but I no longer remember what parmlib member actually
controls the "default".

My last shop typically used half track blocking for disk files (27k) and
we generally received 3 block buffering.



Mon, 30 Jan 2006 03:57:54 GMT  
 BUFNO question

Quote:

>In any given MVS or zOS installation, for simple QSAM file
>processing, is there a default for the BUFNO if I do
>not specify it on the DCB stmt in the JCL?

     I can't point to the documentation, but I believe the answer
is five (5) buffers for DASD and two (2) otherwise.

     When overriding the default, I was taught to use a number
that was a multiple of the number of blocks on a track.

--
Arthur T.  - If address is munged, reply to:  ar23hur "at"
speakeasy "dot" net



Tue, 31 Jan 2006 07:15:49 GMT  
 
 [ 6 post ] 

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