Re: Transaction Speed and real time database

Hannu Krosing wrote:
> Ühel kenal päeval, R, 2006-07-21 kell 13:29, kirjutas Andrew Dunstan:
>   
>> What you are asking is essentially the equivalent of asking "How long is 
>> a piece of string?" The question is meaningless and so will be any 
>> answer. The fact that there are web sites which are happy to supply you 
>> with meaningless information doesn't mean we should follow suit.
>>
>> And frankly, I would be very dubious about using PostgreSQL or just 
>> about any other RDBMS in a Real Time System, hard or soft.
>>     
>
> It would probably be possible to get constant-time inserts into an
> indexless table, once checkpoints are spread out over the whole
> checpoint interval, as described by the NTT staff at the conference, but
> this is probably the only RT compatible scenario you can expect from an
> RDBMS.
>
> Another way to get RT is just use long required completion times and
> light enough load on db that you always meet your time limit. 
>
> Remember, RT does not neccesarily mean Fast it just needs to be
> Predictable!
>
>   

Increasing required time constraints only lowers the likelihood that you
will fail to meet RT requirements, rather than eliminating it.

I suspect that for genuine RT performance we'd need to build in some
sort of preemption mechanism (although I freely confess this isn't my
area of expertise).

cheers

andrew