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)
zhangleiqi...@huawei.com 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
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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) zhangleiqi...@huawei.com
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
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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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