[Gluster-devel] geo-rep regression because of node-uuid change
Karthik Subrahmanya
ksubrahm at redhat.com
Tue Jun 20 10:57:17 UTC 2017
On Tue, Jun 20, 2017 at 4:12 PM, Aravinda <avishwan at redhat.com> wrote:
> I think following format can be easily adopted by all components
>
> UUIDs of a subvolume are seperated by space and subvolumes are separated
> by comma
>
> For example, node1 and node2 are replica with U1 and U2 UUIDs respectively
> and
> node3 and node4 are replica with U3 and U4 UUIDs respectively
>
> node-uuid can return "U1 U2,U3 U4"
>
> Geo-rep can split by "," and then split by space and take first UUID
> DHT can split the value by space or comma and get unique UUIDs list
>
> Another question is about the behavior when a node is down, existing
> node-uuid xattr will not return that UUID if a node is down.
After the change [1], if a node is down we send all zeros as the uuid for
that node, in the list of node uuids.
[1] https://review.gluster.org/#/c/17084/
Regards,
Karthik
> What is the behavior with the proposed xattr?
>
> Let me know your thoughts.
>
> regards
> Aravinda VK
>
>
> On 06/20/2017 03:06 PM, Aravinda wrote:
>
>> Hi Xavi,
>>
>> On 06/20/2017 02:51 PM, Xavier Hernandez wrote:
>>
>>> Hi Aravinda,
>>>
>>> On 20/06/17 11:05, Pranith Kumar Karampuri wrote:
>>>
>>>> Adding more people to get a consensus about this.
>>>>
>>>> On Tue, Jun 20, 2017 at 1:49 PM, Aravinda <avishwan at redhat.com
>>>> <mailto:avishwan at redhat.com>> wrote:
>>>>
>>>>
>>>> regards
>>>> Aravinda VK
>>>>
>>>>
>>>> On 06/20/2017 01:26 PM, Xavier Hernandez wrote:
>>>>
>>>> Hi Pranith,
>>>>
>>>> adding gluster-devel, Kotresh and Aravinda,
>>>>
>>>> On 20/06/17 09:45, Pranith Kumar Karampuri wrote:
>>>>
>>>>
>>>>
>>>> On Tue, Jun 20, 2017 at 1:12 PM, Xavier Hernandez
>>>> <xhernandez at datalab.es <mailto:xhernandez at datalab.es>
>>>> <mailto:xhernandez at datalab.es
>>>> <mailto:xhernandez at datalab.es>>> wrote:
>>>>
>>>> On 20/06/17 09:31, Pranith Kumar Karampuri wrote:
>>>>
>>>> The way geo-replication works is:
>>>> On each machine, it does getxattr of node-uuid and
>>>> check if its
>>>> own uuid
>>>> is present in the list. If it is present then it
>>>> will consider
>>>> it active
>>>> otherwise it will be considered passive. With this
>>>> change we are
>>>> giving
>>>> all uuids instead of first-up subvolume. So all
>>>> machines think
>>>> they are
>>>> ACTIVE which is bad apparently. So that is the
>>>> reason. Even I
>>>> felt bad
>>>> that we are doing this change.
>>>>
>>>>
>>>> And what about changing the content of node-uuid to
>>>> include some
>>>> sort of hierarchy ?
>>>>
>>>> for example:
>>>>
>>>> a single brick:
>>>>
>>>> NODE(<guid>)
>>>>
>>>> AFR/EC:
>>>>
>>>> AFR[2](NODE(<guid>), NODE(<guid>))
>>>> EC[3,1](NODE(<guid>), NODE(<guid>), NODE(<guid>))
>>>>
>>>> DHT:
>>>>
>>>> DHT[2](AFR[2](NODE(<guid>), NODE(<guid>)),
>>>> AFR[2](NODE(<guid>),
>>>> NODE(<guid>)))
>>>>
>>>> This gives a lot of information that can be used to
>>>> take the
>>>> appropriate decisions.
>>>>
>>>>
>>>> I guess that is not backward compatible. Shall I CC
>>>> gluster-devel and
>>>> Kotresh/Aravinda?
>>>>
>>>>
>>>> Is the change we did backward compatible ? if we only require
>>>> the first field to be a GUID to support backward compatibility,
>>>> we can use something like this:
>>>>
>>>> No. But the necessary change can be made to Geo-rep code as well if
>>>> format is changed, Since all these are built/shipped together.
>>>>
>>>> Geo-rep uses node-id as follows,
>>>>
>>>> list = listxattr(node-uuid)
>>>> active_node_uuids = list.split(SPACE)
>>>> active_node_flag = True if self.node_id exists in active_node_uuids
>>>> else False
>>>>
>>>
>>> How was this case solved ?
>>>
>>> suppose we have three servers and 2 bricks in each server. A replicated
>>> volume is created using the following command:
>>>
>>> gluster volume create test replica 2 server1:/brick1 server2:/brick1
>>> server2:/brick2 server3:/brick1 server3:/brick1 server1:/brick2
>>>
>>> In this case we have three replica-sets:
>>>
>>> * server1:/brick1 server2:/brick1
>>> * server2:/brick2 server3:/brick1
>>> * server3:/brick2 server2:/brick2
>>>
>>> Old AFR implementation for node-uuid always returned the uuid of the
>>> node of the first brick, so in this case we will get the uuid of the three
>>> nodes because all of them are the first brick of a replica-set.
>>>
>>> Does this mean that with this configuration all nodes are active ? Is
>>> this a problem ? Is there any other check to avoid this situation if it's
>>> not good ?
>>>
>> Yes all Geo-rep workers will become Active and participate in syncing.
>> Since changelogs will have the same information in replica bricks this will
>> lead to duplicate syncing and consuming network bandwidth.
>>
>> Node-uuid based Active worker is the default configuration in Geo-rep
>> till now, Geo-rep also has Meta Volume based syncronization for Active
>> worker using lock files.(Can be opted using Geo-rep configuration, with
>> this config node-uuid will not be used)
>>
>> Kotresh proposed a solution to configure which worker to become Active.
>> This will give more control to Admin to choose Active workers, This will
>> become default configuration from 3.12
>> https://github.com/gluster/glusterfs/issues/244
>>
>> --
>> Aravinda
>>
>>
>>> Xavi
>>>
>>>
>>>>
>>>>
>>>> Bricks:
>>>>
>>>> <guid>
>>>>
>>>> AFR/EC:
>>>> <guid>(<guid>, <guid>)
>>>>
>>>> DHT:
>>>> <guid>(<guid>(<guid>, ...), <guid>(<guid>, ...))
>>>>
>>>> In this case, AFR and EC would return the same <guid> they
>>>> returned before the patch, but between '(' and ')' they put the
>>>> full list of guid's of all nodes. The first <guid> can be used
>>>> by geo-replication. The list after the first <guid> can be used
>>>> for rebalance.
>>>>
>>>> Not sure if there's any user of node-uuid above DHT.
>>>>
>>>> Xavi
>>>>
>>>>
>>>>
>>>>
>>>> Xavi
>>>>
>>>>
>>>> On Tue, Jun 20, 2017 at 12:46 PM, Xavier Hernandez
>>>> <xhernandez at datalab.es
>>>> <mailto:xhernandez at datalab.es> <mailto:
>>>> xhernandez at datalab.es
>>>> <mailto:xhernandez at datalab.es>>
>>>> <mailto:xhernandez at datalab.es
>>>> <mailto:xhernandez at datalab.es> <mailto:
>>>> xhernandez at datalab.es
>>>> <mailto:xhernandez at datalab.es>>>>
>>>> wrote:
>>>>
>>>> Hi Pranith,
>>>>
>>>> On 20/06/17 07:53, Pranith Kumar Karampuri
>>>> wrote:
>>>>
>>>> hi Xavi,
>>>> We all made the mistake of not
>>>> sending about changing
>>>> behavior of
>>>> node-uuid xattr so that rebalance can use
>>>> multiple nodes
>>>> for doing
>>>> rebalance. Because of this on geo-rep all
>>>> the workers
>>>> are becoming
>>>> active instead of one per EC/AFR subvolume.
>>>> So we are
>>>> frantically trying
>>>> to restore the functionality of node-uuid
>>>> and introduce
>>>> a new
>>>> xattr for
>>>> the new behavior. Sunil will be sending out
>>>> a patch for
>>>> this.
>>>>
>>>>
>>>> Wouldn't it be better to change geo-rep behavior
>>>> to use the
>>>> new data
>>>> ? I think it's better as it's now, since it
>>>> gives more
>>>> information
>>>> to upper layers so that they can take more
>>>> accurate decisions.
>>>>
>>>> Xavi
>>>>
>>>>
>>>> --
>>>> Pranith
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Pranith
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Pranith
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Pranith
>>>>
>>>
>>>
>>
>
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