>
>
> *You are 100% correct that setting the transaction isolation level to READ
> COMMITTED works in the retry loop*.
>
> I stand corrected, and humbled :) Please accept my apologies.
>
Thanks for letting me know :)
>
> One thing I did note, though, is that changing the isolation level of an
> *
regardless, I’d still very much prefer isolation being set here in an explicit
fashion and on a per-transaction basis, rather than across the board, if a
method is known to require it. The advantage of this is that the isolation
level in general can be changed without any risk of the individua
Eugene, I just spent about an hour playing around with an example
scenario in both MySQL and PostgreSQL using READ COMMITTED and
REPEATABLE READ isolation levels. The scenario I used had a single row
being updated, with a loop and a check on rows affected.
*You are 100% correct that setting th
Comments inline:
On Thu, Nov 20, 2014 at 4:34 AM, Jay Pipes wrote:
>
>>
> So while the SELECTs may return different data on successive calls when
> you use the READ COMMITTED isolation level, the UPDATE statements will
> continue to return 0 rows affected **if they attempt to change rows that
>
On 11/19/2014 04:27 PM, Eugene Nikanorov wrote:
Wow, lots of feedback in a matter of hours.
First of all, reading postgres docs I see that READ COMMITTED is the
same as for mysql, so it should address the issue we're discussing:
"/Read Committed/ is the default isolation level in PostgreSQL. Wh
> But the isolation mode change won’t really help here as pointed out by
Jay; discrete transactions have to be used instead.
I still think it will, per postgres documentation (which might look
confusing, but still...)
It actually helps for mysql, that was confirmed. For postgres it appears to
be th
> On Nov 19, 2014, at 4:14 PM, Clint Byrum wrote:
>
>
> One simply cannot rely on multi-statement transactions to always succeed.
agree, but the thing you want is that the transaction either succeeds or
explicitly fails, the latter hopefully in such a way that a retry can be added
which has
Wow, lots of feedback in a matter of hours.
First of all, reading postgres docs I see that READ COMMITTED is the same
as for mysql, so it should address the issue we're discussing:
"*Read Committed* is the default isolation level in PostgreSQL. When a
transaction uses this isolation level, a SELE
> On Nov 19, 2014, at 3:47 PM, Ryan Moats wrote:
>
> >
> BTW, I view your examples from oslo as helping make my argument for
> me (and I don't think that was your intent :) )
>
I disagree with that as IMHO the differences in producing MM in the app layer
against arbitrary backends (Postgresq
Excerpts from Mike Bayer's message of 2014-11-19 10:05:35 -0800:
>
> > On Nov 18, 2014, at 1:38 PM, Eugene Nikanorov
> > wrote:
> >
> > Hi neutron folks,
> >
> > There is an ongoing effort to refactor some neutron DB logic to be
> > compatible with galera/mysql which doesn't support locking
Ian Wells wrote on 11/19/2014 02:33:40 PM:
[snip]
> When you have a plugin that's decided to be synchronous, then there
> are cases where the DB lock is held for a technically indefinite
> period of time. This is basically broken.
A big +1 to this statement
Ryan Moats__
>
>
> Mike Bayer wrote on 11/19/2014 02:10:18 PM:
>
> > From: Mike Bayer
> > To: "OpenStack Development Mailing List (not for usage questions)"
> >
> > Date: 11/19/2014 02:11 PM
> > Subject: Re: [openstack-dev] [Neutron] DB: transaction i
On 19 November 2014 11:58, Jay Pipes wrote:
> Some code paths that used locking in the past were rewritten to retry
>
>> the operation if they detect that an object was modified concurrently.
>> The problem here is that all DB operations (CRUD) are performed in the
>> scope of some transaction th
> On Nov 19, 2014, at 2:58 PM, Jay Pipes wrote:
>
>
>> In other words, the retry logic like the following will not work:
>>
>> def allocate_obj():
>> with session.begin(subtrans=True):
>> for i in xrange(n_retries):
>> obj = session.query(Model).filter_by(filters)
>>
t ?
>
> Ryan Moats
>
> Mike Bayer wrote on 11/19/2014 12:05:35 PM:
>
> > From: Mike Bayer
> > To: "OpenStack Development Mailing List (not for usage questions)"
> >
> > Date: 11/19/2014 12:05 PM
> > Subject: Re: [openstack-dev] [Neutron] D
Hi Eugene, please see comments inline. But, bottom line, is that setting
the transaction isolation level to READ_COMMITTED should be avoided.
On 11/18/2014 01:38 PM, Eugene Nikanorov wrote:
Hi neutron folks,
There is an ongoing effort to refactor some neutron DB logic to be
compatible with gal
014 12:05 PM
> Subject: Re: [openstack-dev] [Neutron] DB: transaction isolation and
> related questions
>
> On Nov 18, 2014, at 1:38 PM, Eugene Nikanorov
wrote:
>
> Hi neutron folks,
>
> There is an ongoing effort to refactor some neutron DB logic to be
> compatible wit
> On Nov 18, 2014, at 1:38 PM, Eugene Nikanorov wrote:
>
> Hi neutron folks,
>
> There is an ongoing effort to refactor some neutron DB logic to be compatible
> with galera/mysql which doesn't support locking (with_lockmode('update')).
>
> Some code paths that used locking in the past were re
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