Hi
I have a number of clients connecting to a DB in order to take jobs off a
queue, mark them active, then run them. In pseudo code, each client executes
the following sequence of queries:
a-- select test_id from tests where status=1 and priority < 11 order by
priority
b-- update tests set status=2 where test_id = <result of query above>
< load,run test etc>
[ eg status==1 -> queued, status==2 -> active]
What happens in some cases is that tests can be marked active by more than one
client. I'm guessing what is happening (if we have two clients C1, C2 ) is
the following sequence of events in the DBMS:
C1a
C2a
C1b
C2b
What's the best way to ensure that a single client executes both a and b
atomically so that no other client can show up and execute an 'a' between
another client's a and b ?
Cheers
Tim
Never be afraid to tell anyone who you are
--Anonymous
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