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https://issues.apache.org/jira/browse/SOLR-11489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16420839#comment-16420839
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Erick Erickson commented on SOLR-11489:
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[~janhoy]
It can take a while for someone to realize they want to do the aliasing for,
say, live and not-live collections and atomically switch. Often this is long
after they've gotten their apps running pointing to the collection rather than
any alias.
So I create C1 and index to it. All my apps reference C1.
Now I want to change my schema but have _no_ service interruption. Currently I
can create C2 and get it ready (index to it, QA, whatever). Once it's ready I
create an alias C1->C2. My apps don't have to change.
If we refused to create an alias with the same name as a pre-existing
collection this would not be possible.
I suppose one could do this with a brief service interruption by shutting the
apps down, deleting C1 and then creating an alias C1->C2 but that's clumsy....
This is one variant, there are others that all boil down basically to "I need
to switch what collections are being used without changing my app or service
interruptions"...
As long as we consciously decide not to support my above scenario that's
perfectly valid, just making sure it's considered...
> Create collections as _foo and auto-create an alias foo->_foo
> -------------------------------------------------------------
>
> Key: SOLR-11489
> URL: https://issues.apache.org/jira/browse/SOLR-11489
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Erick Erickson
> Priority: Major
>
> Spin-off from SOLR-11488. Currently if a collection and an alias have the
> same name we don't test how they're resolved. So an innocent change to the
> code could easily change the behavior (what happens when you have a
> collection old, and an alias old->new and delete collection "old"? Have we
> even defined what _should_ happen?).
> See the discussion at SOLR-11488.
> An alternative proposal to SOLR-11488 (thanks Varun for pointing it out) is
> when creating a collection "foo", actually name it _foo and create an alias
> foo->_foo. Also don't allow the user to create an alias that begins with an
> underscore (and maybe the same for collections? An alias _foo->__foo starts
> to get weird).
> The result would be we'd never have a collection and an alias with the same
> name, which would go a long way to prevent issues going forward.
> This requires we consider the name in state.json to be an implementation
> detail, but the user won't notice. Potential here for the list of aliases to
> be quite large.
> Of course the user could still reference the collection directly as _foo if
> they insisted.
> Establishing this JIRA for discussion of the alternatives.
> Assigning to myself to keep it from getting lost, feel free to take it over
> if you'd like.
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