[Tutor] finally without try or except

[Tino Dai]

On Mon, Jul 30, 2012 at 9:01 PM, Steven D'Aprano <steve at pearwood.info>wrote:

> 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.
>
>
I think that is the process I'm going to take. It doesn't seem as elegant,
but I think it's a good compromise.


>
>  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.
>
>
Yes for reprocessing. :(


-Tino
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