| Pete Dashwood 2004-12-17, 3:55 pm |
| 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:
>
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>
> 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/
>
>
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