Re: Writing records to database.

["Simon Coulter" <shc@xxxxxxxxxxxxxxxxx>]

Hello Rob,

You wrote:
>Forgive me for digging up the dead, (but still warm).  Just got back.

Grave robbing vs. Cradle snatching -- which is worse :)

>Granted changing FRCRATIO can be a performance pig.  But, what about a DR
>situation?  Wouldn't you want all records written to dasd in case of
>abnormal termination?  If I trip on the power cord and it gets yanked,
>what happens to these records?

That's what journalling is for!

However, journalling does not affect the number of records in the program buffer
and those are the only records that would be lost in the event of a power
failure.  The system guarantees that records are written to the journal before
they are written to the file.  However, the records it writes are only those 
that
are in main storage.  If you use blocking in your programs (as you should for
best performance) then you could lose records that are changed but still in the
program buffer.  Records are moved from the program buffer to main storage when
the buffer is full so a large blocking factor will increase the potential number
of records that could be lost.  FRCRATIO(1) will save you from this possibility
but at a serious performance impact.  Journalling is better for performance
because a journal write is a sequential operation -- especially if the receiver
can be isolated to a private disk unit (aka ASP).

If you are concerned about disaster recovery then you must:

        o Use journalling
        o Use commitment control
        o Use a UPS

and possibly:

        o install a generator
        o install a second system

thus you keep your data integrity and you get good performance.  I guess on a
fast system you could run with FRCRATIO(1) but I suspect you would soon reach
saturation on disk arm utilisation because every output operation becomes
synchronous and the queueing multiplier effect will cripple your system.

Regards,
Simon Coulter.
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