Re: DataArea vs. Tables

On 16-May-2011 09:40 , Charles Wilt wrote:

On Mon, May 16, 2011 at 12:31 PM, David Gibbs wrote:

DrFranken wrote:

If you write to a *DTAARA the system forces the write to disk.
Now if you have write cache on your disk controllers the write to
that cache is considered 'well enough' and processing continues.
However if you have no cache (as a low end system with mirrored
disk might have) then the write must be actually to disk.

My perspective on using data areas is that they should be read
mostly / update rarely.

I've never seen them that way....consider that IBM themselves use
data areas to support SQL sequence columns....

It wouldn't seem to make sense to do so if Larry's correct about the
overhead of writing to them.

By implementation, the SEQUENCE object is externalized as the data type *DTAARA. Given that the IBM OS creates the objects and performs the Storage Management, the general\user-created data area [by CRTDTAARA] need not have the same SM characteristics as the data areas created by and for the implementation of the SQL request to CREATE SEQUENCE. However even that may be irrelevant, since as far as any user [DBA, SA, whoever outside of IBM i DB2 development] is concerned, the *DTAARA as implementation object need not ever be directly referenced by the run-time SQL for any\each sequence value.

Regards, Chuck