Re: [rgw multisite] disable specified bucket data sync

[Casey Bodley <cbodley@redhat.com>]

The ability to disable sync per-bucket could certainly be added, but it 
would take some work to get right.

First you'd need a radosgw-admin command to enable/disable sync on a 
given bucket, and store that flag with the bucket instance. We read the 
bucket instance before starting sync on each bucket, so you could skip 
the sync depending on that flag.

However, each zone is trying to sync data from all other zones in its 
zonegroup. So disabling it on zone A, for example, will only prevent 
zone A from pulling changes from other zones. The other zones would 
still be pulling changes from zone A, because they have their own copy 
of the bucket instance. So you'd probably want some way to coordinate 
this setting between zones.

The other challenge would be in the interaction with the 'data changes 
log'. Each zone maintains a log of bucket names that have local changes 
(you can view this with 'radosgw-admin datalog list'). Other zones read 
from this log to decide which buckets they need to sync. However, say 
that zone A reads about a change to bucket1 on zone B. If sync on 
bucket1 is disabled, zone A skips the sync and advances its position in 
zone B's datalog. So if sync on bucket1 is later enabled, zone A won't 
remember that it needs to sync from B.

So I think the trick would be to add special entries to the datalog when 
buckets are enabled/disabled, so that other zones will know to a) update 
their local bucket instance, and b) restart sync if enabled. We might 
also want to restrict the radosgw-admin command to the zonegroup's 
master zone so we can avoid races between enable/disable from different 
zones.

Casey


On 08/02/2016 09:16 PM, Zhangzengran wrote:
>>> Hi Casey:
>>>           Why don’t support stopping specified bucket data sync. Is there any difficulty in implementing the feature?
>>>           Or am I missing something?
>>>
>>>           Thank you !
>>
>> Hi,
>>
>> What would you like to get out of this feature? A way to disable sync on a given bucket temporarily, and turn it back on later? Or just a way to have a subset of buckets that don't ever participate in sync?
>>
>> Do you have a use case for the first? That's not something we'd considered.
>>
>> If you just want to have some buckets that never sync, you might consider serving those out of a separate gateway, in a zone that isn't part of a multisite configuration.
>>
>> Thanks,
>> Casey
> deploy a separate none-sync zone with different endpoint may not a good choice. we hope enable/disable a specified bucket sync could be somewhat flexible. :)
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