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https://issues.apache.org/jira/browse/SOLR-17725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17940666#comment-17940666
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Jan Høydahl commented on SOLR-17725:
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Please clarify your intent with this Jira before continuting with any code
contributions. While I think such a feature would benefit many Solr users, it
would be sad to spend lots of time on a particular direction / implementation
before higher level questions / designs are clarified. As such, you did the
correct ting starting a mailing list thread and a JIRA.
My initial questions:
* Do you intend for this to be a new Solr API, if so what is the proposed API?
or a CLI utility tool to run on a cold index folder?
* Is one of your design goals to avoid the need for 2-3x disk space during the
reindex, since you work on segment level and do merges
* Requring Lucene API change is a potential blocker, I'd not be surprised if
the Lucene project rejects making the "created-version" property writable, so
such a discussion with them would come early
* Obviously a new Solr API needs to play well with SolrCloud as well as other
features such such as shard split / move etc. It could however be acceptable to
implement a "core-level" API first and later a "cluser-level" on top of it
* Challenge the assumption that "in-place" segment level is the best choice
for this feature. Re-index into a new collection due to major schema changes is
also a common use case that this will not address
> Automatically upgrade Solr indexes without needing to reindex from source
> -------------------------------------------------------------------------
>
> Key: SOLR-17725
> URL: https://issues.apache.org/jira/browse/SOLR-17725
> Project: Solr
> Issue Type: Improvement
> Reporter: Rahul Goswami
> Priority: Major
> Attachments: High Level Design.png
>
>
> Today upgrading from Solr version X to X+2 requires complete reingestion of
> data from source. This comes from Lucene's constraint which only guarantees
> index compatibility between the version the index was created in and the
> immediate next version.
> This reindexing usually comes with added downtime and/or cost. Especially in
> case of deployments which are in customer environments and not completely in
> control of the vendor, this proposition of having to completely reindex the
> data can become a hard sell.
> I, on behalf of my employer, Commvault, have developed a way which achieves
> this reindexing in-place on the same index. Also, the process automatically
> keeps "upgrading" the indexes over multiple subsequent Solr upgrades without
> needing manual intervention.
> It comes with the following limitations:
> i) All _source_ fields need to be either stored=true or docValues=true. Any
> copyField destination fields can be stored=false of course, just that the
> source fields (or more precisely, the source fields you care about
> preserving) should be either stored or docValues true.
> ii) The datatype of an existing field in schema.xml shouldn't change upon
> Solr upgrade. Introducing new fields is fine.
> For indexes where this limitation is not a problem (it wasn't for us!), the
> tool can reindex in-place on the same core with zero downtime and
> legitimately "upgrade" the index. This can remove a lot of operational
> headaches, especially in environments with hundreds/thousands of very large
> indexes.
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