openstack team mailing list archive

["Mark Washenberger" <mark.washenberger@xxxxxxxxxxxxx>]

Someone might have already said this (sure wish the listserv sent me mail faster), but we tried out PyMysql and it was exceptionally slow, even under almost no load.

I have a branch in my github that I was using to test out unblocking the database access. For my cases I found that it was unblocked but that it didn't really help performance as much as I had hoped.

branch: https://github.com/markwash/nova/tree/optional-db-api-thread-no-pool

just the relevant commit: https://github.com/markwash/nova/commit/99e38d3df579670808711eb8acd1f96806d8b6f0

"Vishvananda Ishaya" <vishvananda@xxxxxxxxx> said:

> Yes it does.  We actually tried to use a pool at diablo release and it was very
> broken. There was discussion about moving over to a pure-python mysql library, but
> it hasn't been tried yet.
> 
> Vish
> 
> On Mar 1, 2012, at 11:45 AM, Yun Mao wrote:
> 
>> There are plenty eventlet discussion recently but I'll stick my
>> question to this thread, although it's pretty much a separate
>> question. :)
>>
>> How is MySQL access handled in eventlet? Presumably it's external C
>> library so it's not going to be monkey patched. Does that make every
>> db access call a blocking call? Thanks,
>>
>> Yun
>>
>> On Wed, Feb 29, 2012 at 9:18 PM, Johannes Erdfelt <johannes@xxxxxxxxxxx> wrote:
>>> On Wed, Feb 29, 2012, Yun Mao <yunmao@xxxxxxxxx> wrote:
>>>> Thanks for the explanation. Let me see if I understand this.
>>>>
>>>> 1. Eventlet will never have this problem if there is only 1 OS thread
>>>> -- let's call it main thread.
>>>
>>> In fact, that's exactly what Python calls it :)
>>>
>>>> 2. In Nova, there is only 1 OS thread unless you use xenapi and/or the
>>>> virt/firewall driver.
>>>> 3. The python logging module uses locks. Because of the monkey patch,
>>>> those locks are actually eventlet or "green" locks and may trigger a
>>>> green thread context switch.
>>>>
>>>> Based on 1-3, does it make sense to say that in the other OS threads
>>>> (i.e. not main thread), if logging (plus other pure python library
>>>> code involving locking) is never used, and we do not run a eventlet
>>>> hub at all, we should never see this problem?
>>>
>>> That should be correct. I'd have to double check all of the monkey
>>> patching that eventlet does to make sure there aren't other cases where
>>> you may inadvertently use eventlet primitives across real threads.
>>>
>>> JE
>>>
>>>
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> 
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