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From Shawn Heisey <apa...@elyograg.org>
Subject Re: SolrCloud Shard console shows roughly same number of documents?
Date Tue, 31 May 2016 16:34:39 GMT
On 5/31/2016 9:53 AM, Siddhartha Singh Sandhu wrote:
> I was speculating whether sharding is done on: 1. index terms with
> each shard having the whole document space. 2. document space with
> each shard have num(documents/no. of shards) of the documents divided
> between them. 

If the router for the collection is "implicit" then sharding is 100
percent manual.  You decide which shard gets the document when you index
it.  There is no automatic shard routing.

If the router is "compositeId" then the shard is determined by doing a
hash on the value of the uniqueKey field, then looking up which shard
handles that hash in the clusterstate.  This choice can be influenced by
using a composite ID value.  If there are plenty of documents and you
don't use composite IDs, the distribution between shards will be mostly
equal.  The following URL contains some information on composite ID routing:

https://lucidworks.com/blog/2014/01/06/multi-level-composite-id-routing-solrcloud/

Thanks,
Shawn


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