Presented on 8th June 2013 at the first Bangalore Lucene/Solr Meetup.

1. SolrCloud and Shard Splitting
Shalin Shekhar Mangar

2. Bangalore Lucene/Solr Meetup
8th
June 2013
Who am I?
●
Apache Lucene/Solr Committer and PMC member
●
Contributor since January 2008
●
Currently: Engineer at LucidWorks
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Formerly with AOL
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Email: shalin@apache.org
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Twitter: shalinmangar
●
Blog: http://shal.in

3. Bangalore Lucene/Solr Meetup
8th
June 2013
SolrCloud: Overview
●
Distributed searching/indexing
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No single points of failure
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Near Real Time Friendly (push replication)
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Transaction logs for durability and recovery
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Real-time get
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Atomic Updates
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Optimistic Concurrency
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Request forwarding from any node in cluster
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A strong contender for your NoSQL needs as well

4. Bangalore Lucene/Solr Meetup
8th
June 2013

5. Bangalore Lucene/Solr Meetup
8th
June 2013
Document Routing
80000000-bfffffff
00000000-3fffffff
40000000-7fffffff
c0000000-ffffffff
shard1shard4
shard3 shard2
1f27
3c7
1
(MurmurHash
3)
1f27
000
0
1f27 ffffto
(hash)
shard
1
q=my_query
shard.keys=BigCo!
numShards=4
router=compositeId
id = BigCo!doc5

6. Bangalore Lucene/Solr Meetup
8th
June 2013
SolrCloud Collections API
●
/admin/collections?action=CREATE&name=mycollection
– &numShards=3
– &replicationFactor=4
– &maxShardsPerNode=2
– &createNodeSet=node1:8080,node2:8080,node3:8080,...
– &collection.configName=myconfigset
●
/admin/collections?action=DELETE&name=mycollection
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/admin/collections?action=RELOAD&name=mycollection
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/admin/collections?action=CREATEALIAS&name=south
– &collections=KA,TN,AP,KL,...
●
Coming soon: Shard aliases

7. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Background
●
Before Solr 4.3, number of shards had to fixed at the time
of collection creation
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Forced people to start with large number of shards
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If a shard ran too hot, the only fix was to re-index and
therefore re-balance the collection
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Each shard is assigned a hash range
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Each shard also has a state which defaults to 'ACTIVE'

8. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Features
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Seamless on-the-fly splitting – no downtime required
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Retried on failures
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/admin/collections?
action=SPLITSHARD&collection=mycollection
– &shard=shardId
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A lower-level CoreAdmin API comes free!
– /admin/cores?action=SPLIT&core=core0&targetCore=core1&targetCore=core2
– /admin/cores?action=SPLIT&core=core0&path=/path/to/index/1&path=/path/to/index/2

9. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard2_0
Shard1
replic
a
leade
r
Shard2
replic
a
leade
r
Shard3
replic
a
leade
r
Shard2_1
update
Shard Splitting

10. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Mechanism
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New sub-shards created in “construction” state
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Leader starts forwarding applicable updates, which are buffered
by the sub-shards
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Leader index is split and installed on the sub-shards
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Sub-shards apply buffered updates
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Replicas are created for sub-shards and brought up to speed
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Sub-shard becomes “active” and old shard becomes “inactive”

11. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Tips and Gotchas
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Supports collections with a hash based router i.e. “plain”
or “compositeId” routers
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Operation is executed by the Overseer node, not by the
node you requested
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HTTP request is synchronous but operation is async. A
read timeout does not mean failure!
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Operation is retried on failure. Check parent leader's logs
before you re-issue the command or you may end with
more shards than you want

12. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Tips and gotchas
●
Solr Admin GUI is not aware of shard states yet so the
inactive parent shard is also shown in “green”
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The CoreAdmin split command can be used against non-
cloud deployments. It will spread docs alternately among
the sub-indexes
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Inactive shards have to be cleaned up manually. Solr 4.4
will have a delete shard API
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Shard splitting in 4.3 release is buggy. Wait for 4.3.1

13. Bangalore Lucene/Solr Meetup
8th
June 2013
Shard Splitting: Looking towards the future
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GUI integration and better progress reporting/monitoring
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Better support for custom sharding use-cases
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More flexibility towards number of sub-shards, hash
ranges, number of replicas etc
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Store replication factor per shard
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Suggest splits to admins based on cluster state and load

14. Confidential and Proprietary
© 2012 LucidWorks14
About LucidWorks
• Intro to LucidWorks (formerly Lucid Imagination)
– Follow: @lucidworks, @lucidimagineer
– Learn: http://www.lucidworks.com
• Check out SearchHub: http://www.searchhub.org
• Solr 4.1 Reference Guide: http://bit.ly/11KSiMN
– Older versions: http://bit.ly/12t1Egq
• Our Products
– LucidWorks Search
– LucidWorks Big Data
• Lucene Revolution
– http://www.lucenerevolution.com

15. Bangalore Lucene/Solr Meetup
8th
June 2013
Thank you
Shalin Shekhar Mangar
LucidWorks