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From Hank Cohen <hank.co...@altior.com>
Subject RE: HADOOP in Production
Date Tue, 02 Oct 2012 18:05:39 GMT
There is an important difference between real time and real fast

Real time means that system response must meet a fixed schedule.  
Real fast just means sooner is better.

Real time systems always have hard schedules. The schedule could be in microseconds to control
a laser for making masks for semiconductor manufacturing, milliseconds to control the ignition
in your car or flight controls on an F-22 or  seconds for even slower moving processes.  In
real time system missing the schedule can mean that very bad things happen: planes fall from
the sky, your laser printer fries it's imaging drum, factories explode etc.

Most transaction processing is happy with real fast
The folks doing high velocity trading are pretty close to real time but they probably will
be happy with real fast.
If real fast systems miss a schedule then someone loses money.

The reason that RTOS type operating systems are popular for real time applications is that
they don't allow operations to spend indeterminate amounts of time in uninterruptable states.
 Java will never qualify as a real time system because it has garbage collection and garbage
collection can lock up a system for an indefinite amount of time while it goes through marking
and counting.

Hank Cohen



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