Hi,
I am attempting to implement a job queue in a postgres database. There
is a simple job table in which each row represents a job to be run.
There are multiple dispatcher threads that pull jobs off the queue and
run them. I need concurrency control to prevent multiple threads from
dispatching the same job. I think the most elegant place to do this is
in the database itself using row locking (rather than with OS or
application concurrency control mechanisms, which would restrict the
code to a single process or host).
I can get and lock the next job using
job = session.query(Job).with_lockmode('update').first()
However, another thread running the same query would presumably block
until the first releases the lock.
Is there a non-blocking update mode, such that the second thread
returns immediately (and I can look for a different job), or some way
for the query to exclude locked jobs?
Apologies if this is a sqlalchemy 101 (or SQL 101) question, I'm new
to it all and I've not been able to find answers via FAQs/google.
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