This document summarizes a presentation about SolrCloud shard splitting. It introduces the presenter and his background with Apache Lucene and Solr. The presentation covers an overview of SolrCloud, how documents are routed to shards in SolrCloud, the SolrCloud collections API, and the new functionality for splitting shards in Solr 4.3 to allow dynamic resharding of collections without downtime. It provides details on the shard splitting mechanism and tips for using the new functionality.

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
●
Formerly with AOL
●
Email: shalin@apache.org
●
Twitter: shalinmangar
●
Blog: http://shal.in

3. Bangalore Lucene/Solr Meetup
8th
June 2013
SolrCloud: Overview
●
Distributed searching/indexing
●
No single points of failure
●
Near Real Time Friendly (push replication)
●
Transaction logs for durability and recovery
●
Real-time get
●
Atomic Updates
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Optimistic Concurrency
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Request forwarding from any node in cluster
●
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
●
/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
●
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
●
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
●
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
●
HTTP request is synchronous but operation is async. A
read timeout does not mean failure!
●
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