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From Shawn Heisey <s...@elyograg.org>
Subject Re: Switching indexes
Date Wed, 16 Oct 2013 18:40:10 GMT
On 10/16/2013 11:51 AM, Christopher Gross wrote:
> Ok, so I think I was confusing the terminology (still in a 3.X mindset I
> guess.)
> 
> From the Cloud->Tree, I do see that I have "collections" for what I was
> calling "core1", "core2", etc.
> 
> So, to redo the above,
> Servers: index1, index2, index3
> Collections: (on each) coll1, coll2
> Collection (core?) on index1: coll1new
> 
> Each Collection has 1 shard (too small to make sharding worthwhile).
> 
> So should I run something like this:
> http://index1:8080/solr/admin/collections?action=CREATEALIAS&name=coll1&collections=col11new
> 
> Or will I need coll1new to be on each of the index1, index2 and index3
> instances of Solr?

I don't think you can create an alias if a collection already exists
with that name - so having a collection named core1 means you wouldn't
want an alias named core1.  I could be wrong, but just to keep things
clean, I wouldn't recommend it, even if it's possible.

That CREATEALIAS command will only work if coll1new shows up in
/collections and shows green on the cloud graph.  If it does, and you're
using an alias name that doesn't already exist as a collection, then
you're good.

Whether coll1new is living on one server, two servers, or all three
servers doesn't matter for CREATEALIAS, or for most other
collection-related topics.  Any query or update can be sent to any
server in the cloud and it will be routed to the correct place according
to the clusterstate.

Where things live and how many replicas there are *does* matter for a
discussion about redundancy.  Generally speaking, you're going to want
your shards to have at least two replicas, so that if a Solr instance
goes down, or is taken down for maintenance, your cloud remains fully
operational.  In your situation, you probably want three replicas - so
each collection lives on all three servers.

So my general advice:

Decide what name you want your application to use, make sure none of
your existing collections are using that name, and set up an alias with
that name pointing to whichever collection is current.  Then change your
application configurations or code to point at the alias instead of
directly at the collection.

When you want to do your reindex, first create a new collection using
the collections API.  Index to that new collection.  When it's ready to
go, use CREATEALIAS to update the alias, and your application will start
using the new index.

Thanks,
Shawn


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