On 8/6/2013 8:49 PM, manju16832003 wrote:
My Confusion is it feasible to choose many cores or use shards. I do not
have much experience on how shards works and why they are used for. I would
like to know the suggestions :-) for the design like this.
What are the implications if I were to choose to use many cores and handle
stuff at application level calling different cores.
Although shards and cores refer to slightly different things, when it
comes right down to it, it's difficult to separate the two concepts.
Short version: Shards are implemented using cores. The long version
follows below.
A core is a functionally complete Solr index. You can have more than
one core per Solr instance. Multiple cores are discussed in the
CoreAdmin wiki page: http://wiki.apache.org/solr/CoreAdmin
Shards refer to a concept in distributed search. The index is divided
into pieces. The request comes in to Solr. Solr forwards the request
to each shard. It then analyzes each shard result into a combined
result, pulls the requested fields out of each shard, and sends the
response to the requester.
If you are planning a new deployment of a sharded index, you probably
will want to use SolrCloud. It's possible to use shards without
SolrCloud, but SolrCloud automates everything and makes it MUCH easier.
In SolrCloud, a collection is a logical index. A collection is composed
of one or more shards. It is perfectly acceptable to have only one
shard in an index, in which case it won't be using distributed search,
but the following still applies:
Each shard is composed of replicas. If your replicationFactor is 2,
then when your cloud is operating normally, you'll have two replicas of
each shard. If the replicationFactor is 5, then you'll have five
replicas. One of those replicas will be elected as leader for that
shard. You can have a replicationFactor of 1, in which case there will
only be one copy, but it will not be a fault-tolerant setup.
Now for the relationship between shards and cores: Each replica of a
shard *IS* a core. All of the cores in a single collection will
typically have the same configuration and schema.
More info about SolrCloud:
http://wiki.apache.org/solr/SolrCloud
Thanks,
Shawn
