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From Apache Wiki <>
Subject [Solr Wiki] Update of "SolrTerminology" by ShawnHeisey
Date Wed, 18 Sep 2013 19:55:09 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Solr Wiki" for change notification.

The "SolrTerminology" page has been changed by ShawnHeisey:

Added section specifically for SolrCloud.  No changes to the general list, though some may
be required.

+ <<TableOfContents>>
  This is the place to define terms that are specific to Solr or that have meanings in the
Solr community that differ  from their meanings in the general populace.
  When adding to this page, please list terms in alphabetical order.
+ == SolrCloud ==
+ One of the most confusing aspects of Solr terminology is in the difference between collections,
shards, replicas, cores, and config sets.  These terms have specific meanings with reference
to SolrCloud.
+  * '''''Collection''''': A complete logical index in a SolrCloud cluster.  It is associated
with a config set and is made up of one or more shards.  If the number of shards is more than
one, it is a distributed index, but SolrCloud lets you refer to it by the collection name
and not worry about the shards parameter that is normally required for DistributedSearch.
+  * '''''Config Set''''': A set of config files necessary for a core to function properly.
 Each config set has a name.  At minimum this will consist of solrconfig.xml (SolrConfigXml)
and schema.xml (SchemaXml), but depending on the contents of those two files, may include
other files.  This is stored in Zookeeper.  Config sets can be uploaded or updated using the
[[SolrCloud#Command_Line_Util|upconfig command in the command-line utility]] or the [[SolrCloud#Config_Startup_Bootstrap_Params|bootsrap_confdir
Solr startup parameter]].
+  * '''''Core''''': This is discussed in the General list (below) as Solr Core.  One difference
with SolrCloud is that the config it uses is in Zookeeper.  With traditional Solr, the core's
config will be in the conf directory on the disk.
+  * '''''Leader''''': The shard replica that has won the leader election.  Elections can
happen at any time, but normally they are only triggered by events like a Solr instance going
down.  When documents are indexed, SolrCloud will forward them to the leader of the shard,
and the leader will distribute them to all the shard replicas.
+  * '''''Replica''''': One copy of a shard.  Each replica exists within Solr as a core. 
A collection named "test" created with numShards=1 and replicationFactor set to two will have
exactly two replicas, so there will be two cores, each on a different machine (or Solr instance).
 One will be named test_shard1_replica1 and the other will be named test_shard1_replica2.
+  * '''''Shard''''': A logical piece (or slice) of a collection.  Each shard is made up of
one or more replicas.  An election is held to determine which replica is the leader.
+  * '''''Zookeeper''''': This is a program that helps other programs keep a functional cluster
running.  SolrCloud requires [[|Zookeeper]].  It handles leader
elections.  Although Solr can be run with an embedded Zookeeper, it is recommended that it
be standalone, installed separately from Solr.  It is also recommended that it be a redundant
ensemble, requiring at least three hosts.  Zookeeper can run on the same hardware as Solr,
and many users do run it on the same hardware.
+ == General ==
+  * === Foo === foo
   * '''''Auto-warming''''': What Solr does when it opens a new cache, and seeds it with key/val
pairs based on the "top" keys from the old instance of the cache
   * '''''Constraint''''': A viable method of limiting a set of objects ([[|*]])
@@ -25, +42 @@

   * '''''Solr Home Dir''''': Also referred to as the "'''''Solr Home Directory'''''" or just
"'''''Solr Home'''''" this is the main directory where Solr will look for configuration files,
data, and plugins.  Knowing which directory to use as the Solr Home is the one piece of information
that Solr must either assume (the default is "./solr") or be configured using some mechanism
beyond Solr's normal configuration files.  An [[|example
Solr Home]] is included in Solr releases and contains a [[|README.txt]]
explaining the directory structure.  For more information on ways to override the default
Solr Home, please read SolrInstall.
   * '''''Static warming''''': What users can do using newSearcher and firstSearcher event
listeners to force explicit warming actions to be taken when one of these events happens --
frequently it involves seeding one or more caches with values from "static" queries hard coded
in the solrconfig.xml

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