Re: [openstack-dev] [Cinder] Question about synchronized decoration usage in cinder-volume
Thanks for your detailed explanation.
> > 2. Specific to cinder.volume.manager.VolumeManager:attach_volume, all
> operations in "do_attach" method are database related. As said in [1],
> operations to the database will block the main thread of a service, so another
> question I want to know is why this method is needed to be synchronized?
> Currently db operations block the main thread of the service, but hopefully
> this
> will change in the future.
There may be another reason here which is mentioned by DuncanT in IRC a few
days ago. Cinder-backup will also call some methods (at least the
"attach_volume) of manager, and since cinder-backup is a standalone process,
"external=True" should be used here.
--
zhangleiqiang (Trump)
Best Regards
> -Original Message-
> From: Vishvananda Ishaya [mailto:vishvana...@gmail.com]
> Sent: Wednesday, May 07, 2014 12:35 AM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [Cinder] Question about synchronized decoration
> usage in cinder-volume
>
>
> On Apr 26, 2014, at 2:56 AM, Zhangleiqiang (Trump)
> wrote:
>
> > Hi, all:
> >
> > I find almost all of the @utils.synchronized decoration usage in
> cinder-volume (cinder.volume.manager / cinder.volume.drivers.*) with an
> "external=True" param. Such as
> cinder.volume.manager.VolumeManager:attach_volume:
> >
> > def attach_volume(self, context, volume_id, instance_uuid,
> host_name,
> > mountpoint, mode):
> >"""Updates db to show volume is attached."""
> >@utils.synchronized(volume_id, external=True)
> >def do_attach():
> >
> > However, in docstring of common.lockutils.synchronized, I find param
> "external" is used for multi-workers scenario:
> >
> > :param external: The external keyword argument denotes whether
> this lock
> > should work across multiple processes. This means that if two
> different
> > workers both run a a method decorated with
> @synchronized('mylock',
> > external=True), only one of them will execute at a time.
> >
> > I have two questions about it.
> > 1. As far as I know, cinder-api has supported multi-worker mode and
> cinder-volume doesn't support it, does it? So I wonder why the "external=True"
> param is used here?
>
> Before the multibackend support in cinder-volume it was common to run more
> than one cinder-volume for different backends on the same host. This would
> require external=True
> > 2. Specific to cinder.volume.manager.VolumeManager:attach_volume, all
> operations in "do_attach" method are database related. As said in [1],
> operations to the database will block the main thread of a service, so another
> question I want to know is why this method is needed to be synchronized?
> Currently db operations block the main thread of the service, but hopefully
> this
> will change in the future.
>
> Vish
>
> >
> > Thanks.
> >
> > [1]
> http://docs.openstack.org/developer/cinder/devref/threading.html#mysql-acc
> ess-and-eventlet
> > --
> > zhangleiqiang (Trump)
> >
> > Best Regards
> >
> >
> >
> > ___
> > OpenStack-dev mailing list
> > OpenStack-dev@lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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Re: [openstack-dev] [Cinder] Question about synchronized decoration usage in cinder-volume
On Apr 26, 2014, at 2:56 AM, Zhangleiqiang (Trump)
wrote:
> Hi, all:
>
> I find almost all of the @utils.synchronized decoration usage in
> cinder-volume (cinder.volume.manager / cinder.volume.drivers.*) with an
> "external=True" param. Such as
> cinder.volume.manager.VolumeManager:attach_volume:
>
> def attach_volume(self, context, volume_id, instance_uuid,
> host_name,
> mountpoint, mode):
>"""Updates db to show volume is attached."""
>@utils.synchronized(volume_id, external=True)
>def do_attach():
>
> However, in docstring of common.lockutils.synchronized, I find param
> "external" is used for multi-workers scenario:
>
> :param external: The external keyword argument denotes whether
> this lock
> should work across multiple processes. This means that if two different
> workers both run a a method decorated with @synchronized('mylock',
> external=True), only one of them will execute at a time.
>
> I have two questions about it.
> 1. As far as I know, cinder-api has supported multi-worker mode and
> cinder-volume doesn't support it, does it? So I wonder why the
> "external=True" param is used here?
Before the multibackend support in cinder-volume it was common to run more than
one cinder-volume for different backends on the same host. This would require
external=True
> 2. Specific to cinder.volume.manager.VolumeManager:attach_volume, all
> operations in "do_attach" method are database related. As said in [1],
> operations to the database will block the main thread of a service, so
> another question I want to know is why this method is needed to be
> synchronized?
Currently db operations block the main thread of the service, but hopefully
this will change in the future.
Vish
>
> Thanks.
>
> [1]
> http://docs.openstack.org/developer/cinder/devref/threading.html#mysql-access-and-eventlet
> --
> zhangleiqiang (Trump)
>
> Best Regards
>
>
>
> ___
> OpenStack-dev mailing list
> OpenStack-dev@lists.openstack.org
> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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[openstack-dev] [Cinder] Question about synchronized decoration usage in cinder-volume
Hi, all:
I find almost all of the @utils.synchronized decoration usage in
cinder-volume (cinder.volume.manager / cinder.volume.drivers.*) with an
"external=True" param. Such as
cinder.volume.manager.VolumeManager:attach_volume:
def attach_volume(self, context, volume_id, instance_uuid,
host_name,
mountpoint, mode):
"""Updates db to show volume is attached."""
@utils.synchronized(volume_id, external=True)
def do_attach():
However, in docstring of common.lockutils.synchronized, I find param
"external" is used for multi-workers scenario:
:param external: The external keyword argument denotes whether
this lock
should work across multiple processes. This means that if two different
workers both run a a method decorated with @synchronized('mylock',
external=True), only one of them will execute at a time.
I have two questions about it.
1. As far as I know, cinder-api has supported multi-worker mode and
cinder-volume doesn't support it, does it? So I wonder why the "external=True"
param is used here?
2. Specific to cinder.volume.manager.VolumeManager:attach_volume, all
operations in "do_attach" method are database related. As said in [1],
operations to the database will block the main thread of a service, so another
question I want to know is why this method is needed to be synchronized?
Thanks.
[1]
http://docs.openstack.org/developer/cinder/devref/threading.html#mysql-access-and-eventlet
--
zhangleiqiang (Trump)
Best Regards
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