Re: Benefits of asyncio

References	(4 earlier) <878upe8poc.fsf@elektro.pacujo.net> <mailman.10606.1401785234.18130.python-list@python.org> <87wqcyuznv.fsf@elektro.pacujo.net> <mailman.10609.1401787816.18130.python-list@python.org> <87ppiquwyw.fsf@elektro.pacujo.net>
Date	2014-06-03 20:23 +1000
Subject	Re: Benefits of asyncio
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.10611.1401791037.18130.python-list@python.org> (permalink)

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On Tue, Jun 3, 2014 at 8:08 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
> Chris Angelico <rosuav@gmail.com>:
>
>> Okay, but how do you handle two simultaneous requests going through
>> the processing that you see above? You *MUST* separate them onto two
>> transactions, otherwise one will commit half of the other's work.
>
> I will do whatever I have to. Pooling transaction contexts
> ("connections") is probably necessary. Point is, no task should ever
> block.
>
> I deal with analogous situations all the time, in fact, I'm dealing with
> one as we speak.

Rule 1: No task should ever block.
Rule 2: Every task will require the database at least once.
Rule 3: No task's actions on the database should damage another task's
state. (Separate transactions.)
Rule 4: Maximum of N concurrent database connections, for any given value of N.

The only solution I can think of is to have a task wait (without
blocking) for a database connection to be available. That's a lot of
complexity, and you know what? It's going to come to exactly the same
thing as blocking database queries will - your throughput is defined
by your database.

It's the same with all sorts of other resources. What happens if your
error logging blocks? Do you code everything, *absolutely everything*,
around callbacks? Because ultimately, it adds piles and piles of
complexity and inefficiency, and it still comes back to the same
thing: stuff can make other stuff wait.

That's where threads are simpler. You do blocking I/O everywhere, and
the system deals with the rest. Has its limitations, but sure is
simpler.

ChrisA

Thread

Benefits of asyncio Aseem Bansal <asmbansal2@gmail.com> - 2014-06-02 10:40 -0700
  Re: Benefits of asyncio Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-02 12:37 -0600
  Re: Benefits of asyncio Terry Reedy <tjreedy@udel.edu> - 2014-06-02 16:07 -0400
    Re: Benefits of asyncio Roy Smith <roy@panix.com> - 2014-06-02 16:19 -0400
    Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-02 23:28 +0300
      Re: Benefits of asyncio Paul Rubin <no.email@nospam.invalid> - 2014-06-02 13:45 -0700
        Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 07:49 +1000
        Re: Benefits of asyncio Terry Reedy <tjreedy@udel.edu> - 2014-06-02 21:51 -0400
        Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 09:36 +0300
          Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 18:47 +1000
            Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 12:10 +0300
              Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 19:30 +1000
                Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 13:08 +0300
                Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 20:23 +1000
                Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 14:12 +0300
                Re: Benefits of asyncio Paul Rubin <no.email@nospam.invalid> - 2014-06-04 00:52 -0700
              Re: Benefits of asyncio Burak Arslan <burak.arslan@arskom.com.tr> - 2014-06-03 14:05 +0300
              Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 21:57 +1000
              Re: Benefits of asyncio Burak Arslan <burak.arslan@arskom.com.tr> - 2014-06-04 08:10 +0300
              Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-04 17:30 +1000
              Re: Benefits of asyncio Paul Rubin <no.email@nospam.invalid> - 2014-06-04 00:48 -0700
          Re: Benefits of asyncio "Frank Millman" <frank@chagford.com> - 2014-06-03 13:09 +0200
          Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 22:01 +1000
            Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 16:05 +0300
              Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 23:31 +1000
                Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 16:42 +0300
                Re: Benefits of asyncio Chris Angelico <rosuav@gmail.com> - 2014-06-03 23:49 +1000
                Re: Benefits of asyncio Marko Rauhamaa <marko@pacujo.net> - 2014-06-03 19:18 +0300
              Re: Benefits of asyncio Roy Smith <roy@panix.com> - 2014-06-03 11:40 -0400
        Re: Benefits of asyncio Paul Sokolovsky <pmiscml@gmail.com> - 2014-06-03 11:31 +0300
  Re: Benefits of asyncio Burak Arslan <burak.arslan@arskom.com.tr> - 2014-06-03 00:07 +0300
  Re: Benefits of asyncio Aseem Bansal <asmbansal2@gmail.com> - 2014-06-02 21:54 -0700

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