The API that enables master/slave is the ReplicationHandler, where the follower 
(slave) pulls index files from leader (master).
This same API is used in SolrCloud for the PULL replica type, and also as a 
fallback for full recovery if transaction log is not enough. 
So I don’t see it going away anytime soon, even if the non-cloud deployment 
style is less promoted in the documentation.

Jan

> 6. okt. 2020 kl. 16:25 skrev Oakley, Craig (NIH/NLM/NCBI) [C] 
> <craig.oak...@nih.gov.INVALID>:
> 
>> it better not ever be depreciated.  it has been the most reliable mechanism 
>> for its purpose
> 
> I would like to know whether that is the consensus of Solr developers.
> 
> We had been scrambling to move from Master/Slave to CDCR based on the 
> assertion that CDCR support would last far longer than Master/Slave support.
> 
> Can we now assume safely that this assertion is now completely moot? Can we 
> now assume safely that Master/Slave is likely to be supported for the 
> foreseeable future? Or are we forced to assume that Master/Slave support will 
> evaporate shortly after the now-evaporated CDCR support?
> 
> -----Original Message-----
> From: David Hastings <hastings.recurs...@gmail.com> 
> Sent: Wednesday, September 30, 2020 3:10 PM
> To: solr-user@lucene.apache.org
> Subject: Re: Master/Slave
> 
>> whether we should expect Master/Slave replication also to be deprecated
> 
> it better not ever be depreciated.  it has been the most reliable mechanism
> for its purpose, solr cloud isnt going to replace standalone, if it does,
> thats when I guess I stop upgrading or move to elastic
> 
> On Wed, Sep 30, 2020 at 2:58 PM Oakley, Craig (NIH/NLM/NCBI) [C]
> <craig.oak...@nih.gov.invalid> wrote:
> 
>> Based on the thread below (reading "legacy" as meaning "likely to be
>> deprecated in later versions"), we have been working to extract ourselves
>> from Master/Slave replication
>> 
>> Most of our collections need to be in two data centers (a read/write copy
>> in one local data center: the disaster-recovery-site SolrCloud could be
>> read-only). We also need redundancy within each data center for when one
>> host or another is unavailable. We implemented this by having different
>> SolrClouds in the different data centers; with Master/Slave replication
>> pulling data from one of the read/write replicas to each of the Slave
>> replicas in the disaster-recovery-site read-only SolrCloud. Additionally,
>> for some collections, there is a desire to have local read-only replicas
>> remain unchanged for querying during the loading process: for these
>> collections, there is a local read/write loading SolrCloud, a local
>> read-only querying SolrCloud (normally configured for Master/Slave
>> replication from one of the replicas of the loader SolrCloud to both
>> replicas of the query SolrCloud, but with Master/Slave disabled when the
>> load was in progress on the loader SolrCloud, and with Master/Slave resumed
>> after the loaded data passes QA checks).
>> 
>> Based on the thread below, we made an attempt to switch to CDCR. The main
>> reason for wanting to change was that CDCR was said to be the supported
>> mechanism, and the replacement for Master/Slave replication.
>> 
>> After multiple unsuccessful attempts to get CDCR to work, we ended up with
>> reproducible cases of CDCR loosing data in transit. In June, I initiated a
>> thread in this group asking for clarification of how/whether CDCR could be
>> made reliable. This seemed to me to be met with deafening silence until the
>> announcement in July of the release of Solr8.6 and the deprecation of CDCR.
>> 
>> So we are left with the question whether we should expect Master/Slave
>> replication also to be deprecated; and if so, with what is it expected to
>> be replaced (since not with CDCR)? Or is it now sufficiently safe to assume
>> that Master/Slave replication will continue to be supported after all
>> (since the assertion that it would be replaced by CDCR has been
>> discredited)? In either case, are there other suggested implementations of
>> having a read-only SolrCloud receive data from a read/write SolrCloud?
>> 
>> 
>> Thanks
>> 
>> -----Original Message-----
>> From: Shawn Heisey <apa...@elyograg.org>
>> Sent: Tuesday, May 21, 2019 11:15 AM
>> To: solr-user@lucene.apache.org
>> Subject: Re: SolrCloud (7.3) and Legacy replication slaves
>> 
>> On 5/21/2019 8:48 AM, Michael Tracey wrote:
>>> Is it possible set up an existing SolrCloud cluster as the master for
>>> legacy replication to a slave server or two?   It looks like another
>> option
>>> is to use Uni-direction CDCR, but not sure what is the best option in
>> this
>>> case.
>> 
>> You're asking for problems if you try to combine legacy replication with
>> SolrCloud.  The two features are not guaranteed to work together.
>> 
>> CDCR is your best bet.  This replicates from one SolrCloud cluster to
>> another.
>> 
>> Thanks,
>> Shawn
>> 

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