[389-devel] Re: Replication after full online init

On 06/30/2016 11:53 PM, Noriko Hosoi wrote:

On 06/30/2016 12:45 AM, Ludwig Krispenz wrote:

Hi William,

the reason that after  a total init the consumer does not have the latest state of the supplier RUV and is receiving updates based on the RUV at start of the total init is independent of the modrdn problem. When a supplier is performing a total init it is still accepting changes, the total init can take a while and there are scenarios where an entry which is already sent is updated before total init finishes. We cannot loose these changes.

OK...  Then, RUV needs to be created at the time when the supplier starts online init?

it basically is done like that, we could explicitely send the ruv as first entry of an online init, it would then reflect the state of the start of the online init. Instead we send the suppliere ruv as usual in the start repl session and the consumer stores it in the connext and at the end of the online init creates the ruv from this - the effect is the same.

The test case would be something like this?
1. run online init on the supplier.
2. do some operation like move entries against the supplier while the online init is still running on the consumer.
3. do some operation which depends upon the previous operation done in the step 2.
4. check the consumer is healthy or not.

yes, that would have to be tested

Isn't it a timestamp issue from which operation should be replayed after the total update?  Regardless of the way how to fix 48755, unless the step 2 operation(s) are replayed after the online init is done, the consumer could get broken/inconsistent?

step 2 ops will be replicated, they have csns > csn(ruv), but I am concerned that we could moddn an entry, which is not yet sent to a newsuperior which also was not yet sent - and we have the same scenario you wanted to fix with 48755

Thanks,
--noriko

Therfor the update resolution/ entry state resolution on the consumer side has to handle this, ignore changes already applied and apply new changes. And it handles it, if there are bugs they have to be fixed.
Now, I am no longer sure if the fix for 48755 handles correctly all modrdns received after the id list was prepared, the parentid might change while the total init is on progress.
This brings up my origimal suggestion to handle the modrdn problems also on the consumer side.

Ludwig

On 06/30/2016 02:34 AM, William Brown wrote:

Hi,    Now that https://fedorahosted.org/389/ticket/48755 is merged, I would  like to discuss the way we handle CSN with relation to this master. As  I'm not an expert on this topic, I want to get the input of everyone  about this.    Following this document:  http://www.port389.org/docs/389ds/design/changelog-processing-in-repl-state-sending-updates.html      As I understand it, after a full online init, the replica that consumed  the changes does not set it's CSN to match the CSN of the master that  sent the changes.    As a result, after the online init, this causes a number of changes to  be replicated from the sending master to the consumer. These are ignored  by the URP, and we continue.    However, in a number of cases these are *not* ignored, and have caused  us some bugs in replication in the past. We also have some failing  changes that are skipped, which could in certain circumstance lead to  inconsistency in replicas. We have gone to a lot of effort to be able to  skip changes, to handle the case above.    The reason was is that if there was a modrdn performed, and the entry ID  of the entry that was moved was less than the new parent ID, this *had*  to be skipped, so that after the online init the modrdn change was  replayed and applied to the consumer.    Since 48755 which sorts based on the parent ID, this seems to no longer  be an issue. So we don't need to have the master replay it's changelog  out to the consumer, because the consumer is now a literal clone of the  data.     So, is there a reason for us to leave the CSN of the consumer low to  allow this replay to occur? Or can we alter the behaviour of the  consumer to set it's CSN to the CSN of the sending master, so that we  don't need to replay these changes?       

--  389-devel mailing list  389-devel@lists.fedoraproject.org  https://lists.fedoraproject.org/admin/lists/389-devel@lists.fedoraproject.org  

--   Red Hat GmbH, http://www.de.redhat.com/, Registered seat: Grasbrunn,   Commercial register: Amtsgericht Muenchen, HRB 153243,  Managing Directors: Charles Cachera, Michael Cunningham, Michael O'Neill, Eric Shander

--  389-devel mailing list  389-devel@lists.fedoraproject.org  https://lists.fedoraproject.org/admin/lists/389-devel@lists.fedoraproject.org  

--  389-devel mailing list  389-devel@lists.fedoraproject.org  https://lists.fedoraproject.org/admin/lists/389-devel@lists.fedoraproject.org  

--   Red Hat GmbH, http://www.de.redhat.com/, Registered seat: Grasbrunn,   Commercial register: Amtsgericht Muenchen, HRB 153243,  Managing Directors: Charles Cachera, Michael Cunningham, Michael O'Neill, Eric Shander