RE: Re: Terminology question: Core vs. Collection vs...

Darren Govoni Thu, 03 Jan 2013 06:25:31 -0800

Ah, ok. Good. Makes sense.

I think I will draw all this up in a UML that includes the distinction between the 
"logical" terms and the "physical" terms (and their mapping) as they do get 
intertwined. I'll post it here when I'm done.


<br><br><br>------- Original Message -------

On 1/3/2013 09:19 AM Jack Krupansky wrote: A single shard MAY exist on a single core, but only if it is not replicated. Generally, a single shard will exist on multiple cores, each a replica of the source data as it comes into the update handler.

<br>
<br>-- Jack Krupansky
<br>

 -----Original Message----- From: Darren Govoni

<br>Sent: Thursday, January 03, 2013 9:10 AM
<br>To: solr-user@lucene.apache.org
<br>Subject: RE: Re: Terminology question: Core vs. Collection vs...
<br>
<br>Thanks. I got that part.
<br>

 A group of shards (and therefore cores) represent a collection, yes. But a single shard exist only on a single core?

<br>
<br><br><br><br>------- Original Message -------

 On 1/3/2013 09:03 AM Jack Krupansky wrote: No, a shard is a subset (or "slice") of the collection. Sharding is a way of "slicing" the original data, before we talk about how the shards get stored and replicated on actual Solr cores. Replicas are instances of the data for

<br><br>a shard.
<br><br>
<br><br>Sometimes people may loosely speak of a replica as being "a shard", but
<br><br>that's just loose use of the terminology.
<br><br>
<br><br>So, we're not "sharding shards", but we are "replicating shards".
<br><br>
<br><br>-- Jack Krupansky
<br><br>

 -----Original Message----- From: Darren Govoni

<br><br>Sent: Thursday, January 03, 2013 8:51 AM
<br><br>To: solr-user@lucene.apache.org
<br><br>Subject: RE: Re: Terminology question: Core vs. Collection vs...
<br><br>
<br><br>Thanks again. (And sorry to jump into this convo)
<br><br>
<br><br>But I had a question on your statement:
<br><br>
<br><br>On 1/3/2013 08:07 AM Jack Krupansky wrote:

 Collection is the more modern term and incorporates the fact that the collection may be sharded, with each shard on one or more cores, with each core being a replica of the other cores within that shard of that

<br><br><br>collection.
<br><br>
<br><br>A collection is sharded, meaning it is distributed across cores. A shard
<br><br>itself is not distributed across cores in the same since. Rather a shard

 exist on a single core and is replicated on other cores. Is that right? The

<br><br>way its worded above, it sounds like a shard can also be sharded...
<br><br>
<br><br>
<br><br><br><br><br>------- Original Message -------
<br><br>On 1/3/2013  08:28 AM Jack Krupansky wrote:<br>A node is a machine in a
<br><br>cluster or cloud (graph). It could be a real

 machine or a virtualized machine. Technically, you could have multiple virtual nodes on the same physical "box". Each Solr replica would be on

<br><br>a
<br><br><br>different node.
<br><br><br>

 Technically, you could have multiple Solr instances running on a single hardware node, each with a different port. They are simply instances of Solr, although you could consider each Solr instance a node in a Solr

<br><br>cloud
<br><br><br>as well, a "virtual" node. So, technically, you could have multiple
<br><br>replicas

 on the same node, but that sort of defeats most of the purpose of having replicas in the first place - to distribute the data for performance and fault tolerance. But, you could have replicas of different shards on the

<br><br><br>same node/box for a partial improvement of performance and fault
<br><br>tolerance.
<br><br><br>
<br><br><br>A Solr "cloud' is really a cluster.
<br><br><br>
<br><br><br>-- Jack Krupansky
<br><br><br>

 -----Original Message----- From: Darren Govoni

<br><br><br>Sent: Thursday, January 03, 2013 8:16 AM
<br><br><br>To: solr-user@lucene.apache.org
<br><br><br>Subject: RE: Re: Terminology question: Core vs. Collection vs...
<br><br><br>
<br><br><br>Good write up.
<br><br><br>
<br><br><br>And what about "node"?
<br><br><br>
<br><br><br>I think there needs to be an official glossary of terms that is
<br><br>sanctioned
<br><br><br>by the solr team and some terms still ni use may need to be labeled
<br><br><br>"deprecated". After so many years, its still confusing.
<br><br><br>
<br><br><br><br><br><br>------- Original Message -------

 On 1/3/2013 08:07 AM Jack Krupansky wrote: Collection is the more

<br><br>modern
<br><br><br>term and incorporates the fact that the
<br><br><br><br>collection may be sharded, with each shard on one or more cores,
<br><br>with
<br><br><br>each

 core being a replica of the other cores within that shard of that

<br><br><br><br>collection.
<br><br><br><br>
<br><br><br><br>Instance is a general term, but is commonly used to refer to a
<br><br>running
<br><br><br>Solr
<br><br><br><br>server, each of which can service any number of cores. A sharded
<br><br><br>collection
<br><br><br><br>would typically require multiple instances of Solr, each with a
<br><br>shard of
<br><br><br>the
<br><br><br><br>collection.
<br><br><br><br>

 Multiple collections can be supported on a single instance of Solr.

<br><br>They

 don't have to be sharded or replicated. But if they are, each Solr

<br><br><br>instance

 will have a copy or replica of the data (index) of one shard of each

<br><br><br>sharded
<br><br><br><br>collection - to the degree that each collection needs that many
<br><br>shards.
<br><br><br><br>
<br><br><br><br>At the API level, you talk to a Solr instance, using a host and
<br><br>port,
<br><br><br>and

 giving the collection name. Some operations will refer only to the

<br><br><br>portion
<br><br><br><br>of a multi-shard collection on that Solr instance, but typically
<br><br>Solr
<br><br><br>will

 "distribute" the operation, whether it be an update or a query, to

<br><br>all
<br><br><br>of
<br><br><br><br>the shards of the named collection. In the case of update, the
<br><br>update
<br><br><br>will
<br><br><br><br>be distributed to all replicas as well, but in the case of query
<br><br>only
<br><br><br>one
<br><br><br><br>replica of each shard of the collection is needed.
<br><br><br><br>

 Before SolrCloud we Solr had master and slave and the slaves were

<br><br><br>replicas
<br><br><br><br>of the master, but with SolrCloud there is no master and all the
<br><br><br>replicas of

 the shard are peers, although at any moment of time one of them will

<br><br>be

 considered the "leader" for coordination purposes, but not in the

<br><br>sense
<br><br><br>that
<br><br><br><br>it is a master of the other replicas in that shard. A SolrCloud
<br><br>replica
<br><br><br>is a

 replica of the data, in an abstract sense, for a single shard of a

<br><br><br><br>collection. A SolrCloud replica is more of an instance of the
<br><br><br>data/index.
<br><br><br><br>
<br><br><br><br>An index exists at two levels: the portion of a collection on a
<br><br>single
<br><br><br>Solr

 core will have a Lucene index, but collectively the Lucene indexes

<br><br>for
<br><br><br>the
<br><br><br><br>shards of a collection can be referred to the index of the
<br><br>collection.
<br><br><br>Each
<br><br><br><br>replica is a copy or instance of a portion of the collection's
<br><br>index.
<br><br><br><br>

 The term slice is sometimes used to refer collectively to all of the cores/replicas of a single shard, or sometimes to a single replica

<br><br>as it
<br><br><br><br>contains only a "slice" of the full collection data.
<br><br><br><br>
<br><br><br><br>-- Jack Krupansky
<br><br><br><br>

 -----Original Message----- From: Alexandre Rafalovitch

<br><br><br><br>Sent: Thursday, January 03, 2013 4:42 AM
<br><br><br><br>To: solr-user@lucene.apache.org
<br><br><br><br>Subject: Terminology question: Core vs. Collection vs...
<br><br><br><br>
<br><br><br><br>Hello,
<br><br><br><br>

 I am trying to understand the core Solr terminology. I am looking

<br><br>for

 correct rather than loose meaning as I am trying to teach an example

<br><br><br>that

 starts from easy scenario and may scale to multi-core, multi-machine

<br><br><br><br>situation.
<br><br><br><br>

 Here are the terms that seem to be all overlapping and/or crossing

<br><br>over
<br><br><br>in
<br><br><br><br>my mind a the moment.
<br><br><br><br>
<br><br><br><br>1) Index
<br><br><br><br>2) Core
<br><br><br><br>3) Collection
<br><br><br><br>4) Instance
<br><br><br><br>5) Replica (Replica of _what_?)
<br><br><br><br>6) Others?
<br><br><br><br>
<br><br><br><br>I tried looking through documentation, but either there is a
<br><br>terminology
<br><br><br><br>drift or I am having trouble understanding the distinctions.
<br><br><br><br>

 If anybody has a clear picture in their mind, I would appreciate a

<br><br><br><br>clarification.
<br><br><br><br>
<br><br><br><br>Regards,
<br><br><br><br>   Alex.
<br><br><br><br>
<br><br><br><br>Personal blog: http://blog.outerthoughts.com/
<br><br><br><br>LinkedIn: http://www.linkedin.com/in/alexandrerafalovitch

 - Time is the quality of nature that keeps events from happening all

<br><br>at

 once. Lately, it doesn't seem to be working. (Anonymous - via GTD

<br><br><br>book)
<br><br><br><br>
<br><br><br><br>
<br><br><br>
<br><br><br>
<br><br>

 

<br>

RE: Re: Terminology question: Core vs. Collection vs...

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