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
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