Re: MAINFRAME SHOP STANDARDS (VSAM)

Thanks Arnold.

I see CICS as a special case, but you were right to point it out.

My comments regarding QSAM vs VSAM/ESDS should be taken as applying OUTSIDE
the CICS environment.

Pete.
(top post).

"Arnold Trembley" <arnold.trembley@worldnet.att.net> wrote in message
news:SAsvd.1089328$Gx4.509542@bgtnsc04-news.ops.worldnet.att.net...
>
>
> Pete Dashwood wrote:
> 
relative 
duplicated 
time 
that 
reclaim 
the 
Unisys) 
for 
put 
utility as 
it 
still 
to 
>
> VSAM ESDS (VSAM sequential files) are used very commonly in CICS for
> writing transaction logs.  That's because using QSAM files in CICS is
> a bit...difficult.  A VSAM ESDS file can easily be open for both input
> and output in CICS.  Not so for QSAM which requires CICS DCT entries
> (Destination Control Table).
>
> In CICS you can specify in the FCT entry that a VSAM file is a data
> table.  You must specify the maximum number of records.  The entire
> file is cached in memory, which means access is much faster, but the
> programs need to be recompiled.  There are two types of VSAM data
> tables - CICS maintained, where CICS periodically flushes buffers to
> the disk, and User maintained, where the file is never copied back to
> disk.
>
> I support applications with both CICS maintained and User Maintained
> VSAM data tables.  For User Maintained tables we define an extra FCT
> entry that points to the same file, without defining it as a data
> table.  We have "sweeper" programs that run at timed intervals to read
> from the UMT and write to the disk version of the file.
>
> It's still a good idea to reorg VSAM KSDS files periodically,
> especially if there's a high volume of insert and delete activity, but
>   you can go for quite a while before performance degrades.
>
> I have never needed to use a VSAM RRDS file, and I'm not sure if RRDS
> supports variable length records.  Obviously, variable length records
> are well supported for VSAM KSDS and ESDS files.
>
> And as was stated elsewhere, I can easily define my own VSAM file, but
> I cannot get a new DB2 table created.  Only a DBA can do that for me.
>
> With kindest regards,
>
> --
> http://arnold.trembley.home.att.net/
> 
>