Open Stack

On 12/02/13 at 09:08am, Russell Bryant wrote:
>On 12/02/2013 09:02 AM, Victor Sergeyev wrote:
>> Hi folks!
>>
>> At the moment I and Roman Podoliaka are working on splitting of
>> openstack.common.db code into a separate library. And it would be nice
>> to drop dependency on eventlet before oslo.db is released.
>>
>> Currently, there is only one place in oslo.db where we use eventlet -
>> wrapping of DB API method calls to be executed by tpool threads. It
>> wraps DB API calls to be executed by tpool threads. This is only needed
>> when eventlet is used together with DB-API driver implemented as a
>> Python C extension (eventlet can't monkey patch C code, so we end up
>> with DB API calls blocking all green threads when using Python-MySQLdb).
>> eventlet has a workaround known as 'tpool' which is basically a pool of
>> real OS threads that can play nicely with eventlet event loop. tpool
>> feature is experimental and known to have stability problems. There is a
>> doubt that anyone is using it in production at all. Nova API (and
>> probably other API services) has an option to prefork the process on
>> start, so that they don't need to use tpool when using eventlet together
>> Python-MySQLdb.
>>
>> We'd really like to drop tpool support from oslo.db, because as a
>> library we should not be bound to any particular concurrency model. If a
>> target project is using eventlet, we believe, it is its problem how to
>> make it play nicely with Python-MySQLdb lib, but not the problem of
>> oslo.db. Though, we could put tpool wrapper into another helper module
>> within oslo-incubator.
>>
>> But we would really-really like not to have any eventlet related code in
>> oslo.db.
>>
>> Are you using CONF.database.use_tpool in production? Does the approach
>> with a separate tpool wrapper class seem reasonable? Or we can just drop
>> tpool support at all, if no one is using it?
>
>Please don't remove it completely.  Putting it in oslo-incubator for now
>seems fine, though.

+1.  We are using it in production, though only in certain places 
because it does have stability issues that we'd like to track down and 
fix.

>
>-- 
>Russell Bryant
>
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