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From "Darren Govoni" <dar...@ontrenet.com>
Subject RE: Re: Terminology question: Core vs. Collection vs...
Date Thu, 03 Jan 2013 13:16:35 GMT
Good write up. 

And what about "node"?

I think there needs to be an official glossary of terms that is sanctioned by the solr team
and some terms still ni use may need to be labeled "deprecated". After so many years, its
still confusing.

<br><br><br>------- Original Message -------
On 1/3/2013  08:07 AM Jack Krupansky wrote:<br>Collection is the more modern term and
incorporates the fact that the 
<br>collection may be sharded, with each shard on one or more cores, with each 
<br>core being a replica of the other cores within that shard of that 
<br>collection.
<br>
<br>Instance is a general term, but is commonly used to refer to a running Solr 
<br>server, each of which can service any number of cores. A sharded collection 
<br>would typically require multiple instances of Solr, each with a shard of the 
<br>collection.
<br>
<br>Multiple collections can be supported on a single instance of Solr. They 
<br>don't have to be sharded or replicated. But if they are, each Solr instance 
<br>will have a copy or replica of the data (index) of one shard of each sharded 
<br>collection - to the degree that each collection needs that many shards.
<br>
<br>At the API level, you talk to a Solr instance, using a host and port, and 
<br>giving the collection name. Some operations will refer only to the portion 
<br>of a multi-shard collection on that Solr instance, but typically Solr will 
<br>"distribute" the operation, whether it be an update or a query, to all of 
<br>the shards of the named collection. In the case of update, the update will 
<br>be distributed to all replicas as well, but in the case of query only one 
<br>replica of each shard of the collection is needed.
<br>
<br>Before SolrCloud we Solr had master and slave and the slaves were replicas 
<br>of the master, but with SolrCloud there is no master and all the replicas of 
<br>the shard are peers, although at any moment of time one of them will be 
<br>considered the "leader" for coordination purposes, but not in the sense that 
<br>it is a master of the other replicas in that shard. A SolrCloud replica is a 
<br>replica of the data, in an abstract sense, for a single shard of a 
<br>collection. A SolrCloud replica is more of an instance of the data/index.
<br>
<br>An index exists at two levels: the portion of a collection on a single Solr 
<br>core will have a Lucene index, but collectively the Lucene indexes for the 
<br>shards of a collection can be referred to the index of the collection. Each 
<br>replica is a copy or instance of a portion of the collection's index.
<br>
<br>The term slice is sometimes used to refer collectively to all of the 
<br>cores/replicas of a single shard, or sometimes to a single replica as it 
<br>contains only a "slice" of the full collection data.
<br>
<br>-- Jack Krupansky
<br>
<br>-----Original Message----- 
<br>From: Alexandre Rafalovitch
<br>Sent: Thursday, January 03, 2013 4:42 AM
<br>To: solr-user@lucene.apache.org
<br>Subject: Terminology question: Core vs. Collection vs...
<br>
<br>Hello,
<br>
<br>I am trying to understand the core Solr terminology. I am looking for
<br>correct rather than loose meaning as I am trying to teach an example that
<br>starts from easy scenario and may scale to multi-core, multi-machine
<br>situation.
<br>
<br>Here are the terms that seem to be all overlapping and/or crossing over in
<br>my mind a the moment.
<br>
<br>1) Index
<br>2) Core
<br>3) Collection
<br>4) Instance
<br>5) Replica (Replica of _what_?)
<br>6) Others?
<br>
<br>I tried looking through documentation, but either there is a terminology
<br>drift or I am having trouble understanding the distinctions.
<br>
<br>If anybody has a clear picture in their mind, I would appreciate a
<br>clarification.
<br>
<br>Regards,
<br>   Alex.
<br>
<br>Personal blog: http://blog.outerthoughts.com/
<br>LinkedIn: http://www.linkedin.com/in/alexandrerafalovitch
<br>- Time is the quality of nature that keeps events from happening all at
<br>once. Lately, it doesn't seem to be working.  (Anonymous  - via GTD book) 
<br>
<br>

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