Say I have two running programs and both of them periodically want to
increment a value in a database. How can I do this so that the increments
will be performed correctly even if the two programs try to do them at the
same time?
If I have code like this:
$x = read_value_from_database();
++$x;
write_value_to_database($x);
then the problem is that both programs might try and do their reads at the
same time, then increment their own copies of the number, and then write
back the same, incremented number. If the database system queues requests
properly, then it won't give any error messages, but the final value of the
number in the database will be 1 greater than what it was before, instead
of what it should be, which is 2 greater.
Is there a single command to increment a numeric value in a database? That
way, the database program could queue those requests, run them in order,
and always end up with the stored number having the right value.
-Bennett
[EMAIL PROTECTED] http://www.peacefire.org
(425) 649 9024
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