On 02/03/2011 08:23 PM, Tom Lane wrote:
Mage<mage@xxxxxxx> writes:
The main question is that isn't "insert into ... select ... where not
exists" atomic?
No, it isn't: it *will* fail in the presence of other transactions doing
the same thing, because the EXISTS test will only see rows that
committed before the command started. You might care to read the
manual's chapter about concurrency:
http://www.postgresql.org/docs/9.0/static/mvcc.html
Thank you, Tom. I will read that.
However I googled a bit before written this trigger and I would like to
ask you: what is the best practice for doing "insert or update"-like
thing, especially in this case, in trigger? I would use lock table from
now. Is it the recommended way?
(I just don't like the "insert -> on exception -> update" method).
Mage
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