[jira] [Commented] (SOLR-13396) SolrCloud will delete the core data for any core that is not referenced in the clusterstate

["Colvin Cowie (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-13396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17682548#comment-17682548 ] 

Colvin Cowie commented on SOLR-13396:
-------------------------------------

I've created a draft PR to add a flag to just disable this behavior, [https://github.com/apache/solr/pull/1321]. It still needs a test and some other things, but hopefully it's a starting point for discussion and getting this fixed in Solr itself.

 
{quote}[~caomanhdat] added a comment - 04/Oct/19 13:39
Yeah I mean rather than coming up with something complicated. Should we just improve the logic here so most of the cases will be solved. I.E: check existence of clusterstate before delete core.
{quote}
I think that even with improvements to the logic, I would still prefer to have an override that disables automatic deletion of cores. In fact I would prefer to have to explicitly enable automatic deletion if I want to opt-in to it.

Personally, I think the only time I want a core to be deleted automatically is if the creation of a new collection/core fails. Otherwise it just makes me very nervous. I can always clean things up manually, but I can't undelete without a fresh backup (though obviously regular backups are needed as well but that's not the point for me).

> SolrCloud will delete the core data for any core that is not referenced in the clusterstate
> -------------------------------------------------------------------------------------------
>
>                 Key: SOLR-13396
>                 URL: https://issues.apache.org/jira/browse/SOLR-13396
>             Project: Solr
>          Issue Type: Bug
>          Components: SolrCloud
>    Affects Versions: 7.3.1, 8.0
>            Reporter: Shawn Heisey
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> SOLR-12066 is an improvement designed to delete core data for replicas that were deleted while the node was down -- better cleanup.
> In practice, that change causes SolrCloud to delete all core data for cores that are not referenced in the ZK clusterstate.  If all the ZK data gets deleted or the Solr instance is pointed at a ZK ensemble with no data, it will proceed to delete all of the cores in the solr home, with no possibility of recovery.
> I do not think that Solr should ever delete core data unless an explicit DELETE action has been made and the node is operational at the time of the request.  If a core exists during startup that cannot be found in the ZK clusterstate, it should be ignored (not started) and a helpful message should be logged.  I think that message should probably be at WARN so that it shows up in the admin UI logging tab with default settings.



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