Re: Commit or Journal?

["Kahn, David" <KAHN@xxxxxxxxxxxxxxxxxx>]

Dean Asmussen (DAsmussen@aol.com) wrote:

>The timestamp can be inadequate unless you're using the new
>"extended length" time -- my old employer had (packaged) programs
>start blowing up when the "D" models came out because some of
>them based unique keys on the old "TIME" keyword. Seems the "D"
>facilitated processing multiple records within the same second.

Dean,

Yes, several records could contain the same timestamp value, but that
doesn't really matter for this purpose. We're only concerned with
multiple updates to the same record in an interactive process. To get a
double update here, the record would have to be updated, read by 2
different users, then updated again by one of them, all before the
timestamp value had moved on. Is this feasible? I doubt it, but it's a
valid point.

It was the full 26 position timestamp that I had in mind, but I'm not
sure it makes any difference. Don't the micro-seconds always get
generated as zero by RPG programs, at least on CISC machines? So if you
believe the above scenario is possible the extended timestamp doesn't
help.

>Method 3?

Method 3 is to have an update counter in the master file record and test
that. It would be set to zero on first write and then incremented every
time the record is updated. It then doesn't matter how close together
the updates come. You might want a timestamp on the record anyway, so
it's a pity to have to have an extra field. If there were a way of using
the micro-seconds part of the timestamp as the counter it could be quite
neat. The stored micro-second value would be a fiddle, but how
meaningful a value is it anyway? However, I'm not sure it's possible in
RPG.


Dave Kahn - TCO, Tengiz, Kazakstan
=========

e-mail:  kahn@tengizchevroil.com    (until September 30th)
         dkahn@cix.compulink.co.uk  (from  October 1st)
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