Tino Dai wrote:
Yes, but that would involve surrounding the entire method with a try except
finally block. I was
told by the Python-Guru-In Residence that shouldn't emulate Java code in
Python, and that was
generally bad programming practice (no flame war intended)
And that is correct. It is *generally* bad programming practice. But that
doesn't mean it is *always* bad programming practice.
*This* is terrible practice:
try:
main()
except:
print("an error occurred")
# but you'll never know what it was, or be able to fix it ha ha!
But this is perfectly reasonable:
try:
main()
finally:
cleanup()
You probably want to rethink your process. You can write the item log
to the db in the except clause but this can be buggy as a second ctrl-c
will stop it.
If you want to be robust, it is best not to try to beat the database. That
means you should write to the database as soon as you can, as often as you
need to, and let the database do what it does best: reliable transaction
storage. Any decent database will guarantee ACID compliance (atomicity,
consistency, isolation, durability).
But sometimes you need to compromise on robustness for speed or convenience.
[...]
This is how the program was originally structured, but we found performance
problems with in.
It's using Django and an Oracle DB, which is notoriously bad for single
record read/writes. So, I
figured why don't we append them all to an array, and write them out at the
end of the program.
I suggest you periodically check the item log, and if there are more than
(say) 20 items, you write them to the database and clear the temporary list.
That way, the number of item logs should never get too large, and the
performance shouldn't suffer too greatly. You will need to tweak that number
to be more or less depending on how poorly the Oracle DB performs.
Then, at the very end of the program, you write whatever items are left in a
finally clause, or atexit. That way, the finally clause should be nice and
speedy and the user is unlikely to hit Ctrl-C a second time.
This will be the most robust as it will
also work for cases where the program is terminated without the use of
the keyboard (i.e. kill -9, task manager, computer reboot, etc.) but
That unfortunately is not so. kill -9 does *not* send a signal or raise an
exception. It just kills the process dead, instantly and without warning.
Likewise for cases when somebody trips over the power cord and disconnects the
server from the power. (Really paranoid sys admins insist on having two power
supplies connected to two different UPSes for their servers.)
it might also slow the program down. You could also try writing the
item log to a local file using pickle or csv.
Better is to use the logging module rather than to reinvent the wheel.
Do your item logs actually need to go in the database? Perhaps you could just
write them to a local log file and leave the database for more critical records.
--
Steven
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