Solr Cloud allows Solr to be distributed and run across multiple servers for increased performance, scalability, availability, and elasticity. It uses Zookeeper for coordination and shares an index across multiple cores and collections. Documents are routed and replicated to shards and replicas based on a hashing function or custom routing rules to partition the data. Queries are distributed and results merged to provide scalable search across an elastic, fault-tolerant cluster.

1. Scaling with Solr Cloud Saumitra Srivastav saumitra.srivastav@glassbeam.com Bangalore Apache Solr Group September-2014 Meetup

2. What is Solr Cloud?
-set of features which add distributed capabilities in Solr
-fault tolerance and high availability
-distributed indexing and search
-enable and simplify horizontal scaling a search index using sharding and replication

3. Non-Cloud Single Node Deployment
Machine(server) - 1
Solr Node ( jetty on port 8983 )
Core - 1
Conf
Data
Core - 2
Conf
Data
Core - N
Conf
Data
......... .........

4. Use Solr Cloud for ...
-performance
-scalability
-high-availability
-simplicity
-elasticity

5. Solr Cloud Glossary
-Cluster
-Node
-Shard
-Leader & Replica
-Overseer
-Collection
-Zookeeper

6. High Level View

7. Glossary
-Cluster
-set of solr nodes
-Node
-a JVM instance running Solr.
-also known as a Solr server.
-Core
-an individual Solr instance (represents a logical index).
-multiple cores can run on a single node.

8. Glossary
-Collection
-one or more documents grouped together in a single logical index.
-can be spread across multiple cores.
-Shard
-a logical section of a single collection
-Implemented as core
-Replica
-A copy of a shard or single logical index
-used in failover or load balancing.

9. Glossary
-Leader
-The main node for each shard that routes document adds, updates, or deletes to other replicas
-if leader goes down, a new node will be elected to take it's place
-Overseer
-A single node in SolrCloud that is responsible for processing actions involving the entire cluster
-if overseer goes down, a new node will be elected to take it's place

10. Zookeeper
-distributed coordination
-maintaining configuration information
Solr Node 1 10.0.0.1:8983
Solr Node 3 10.0.0.3:8983
Solr Node 2 10.0.0.2:8983
Solr Node 4 10.0.0.4:8983
Zookeeper

11. Zookeeper
Solr Node 1 10.0.0.1:8983
Solr Node 3 10.0.0.3:8983
Solr Node 2 10.0.0.2:8983
Solr Node 4 10.0.0.4:8983
zk-1:2181
zk-2:2182
zk-3:2183
Quorum
Client

12. Zookeeper - Central Configuration

13. Zookeeper - distributed coordination
-Keep track of /live_nodes
-Collection metadata and replica state in /clusterstate.json
-Alias list in /aliasies.json
-Leader election

14. Collections
-Collection is a distributed index defined by:
-named configuration
-stored in ZooKeeper
-number of shards
-replication factor
-Number of copies of each document in the collection
-document routing strategy:
-how documents get assigned to shards

15. Collections API
localhost:8983/solr/admin/collections?action=CREATE &name=collection1 &numShards=4 &replicationFactor=2 &maxShardsPerNode=1 &createNodeSet=localhost:8933 &collection.configName=collection1Config

16. Collections

17. Sharding
-Collection has a fixed number of shards
-existing shards can be split
-When to shard?
-Large number of docs
-Large document sizes
-Parallelization during indexing and queries
-Data partitioning (custom hashing)

18. Replication
-Why replicate?
-High-availability
-Load balancing
-How does it work in SolrCloud?
-Near-real-time, NOT master-slave
-Leader forwards to replicas in parallel, waits for response
-Error handling during indexing is tricky

19. Indexing

20. Indexing
1.Get cluster state from ZK
2.Route document directly to leader (hash on doc ID)
3.Persist document on durable storage (tlog)
4.Forward to healthy replicas
5.Acknowledge write succeed to client

21. Querying

22. Querying
-Query client can be ZK aware or just query via a load balancer
-Client can send query to any node in the cluster
-Controller node distributes the query to a replica for each shard to identify documents matching query
-Controller node sorts the results from step 3 and issues a second query for all fields for a page of results

23. Transaction Log (tlog)
-file where the raw documents are written for recovery purposes
-each node has its own tlog
-replayed on server restart
-in case of non gracefull shutdown
-“rolled over” automatically on hard commit
-old one is closed and a new one is opened

24. Transaction Log (tlog)

25. Commits
-Hard Commit & Soft Commit
-Hard commits are about durability, soft commits are about visibility
-Further reading: https://lucidworks.com/blog/understanding- transaction-logs-softcommit-and-commit-in- sorlcloud/

26. What happens on hard Commit?
-The tlog is truncated.
-A new tlog is started.
-Old tlogs will be deleted if there are more than 100 documents in newer tlogs.
-The current index segment is closed and flushed.
-Background segment merges may be initiated.

27. What happens on soft commit?
-The tlog has NOT been truncated. It will continue to grow.
-New documents WILL be visible.
-some caches will have to be reloaded
-top-level caches will be invalidated.

28. Shard Splitting
-Can split shards into two sub-shards
-Live splitting. No downtime needed.
-Requests start being forwarded to sub-shards automatically
-Expensive operation: Use as required during low traffic

29. Overseer
-Persists collection state change events to zooKeeper
-Controller for Collection API commands
-One per cluster (for all collections); elected using leader election
-Asynchronous (pub/sub messaging)
-Automated failover to a healthy node
-Can be assigned to a dedicated node

30. Overseer

31. Controlling data partitioning
-Shard vs Replicas
-Custom Routing
-Collection Aliasing

32. Shard vs Replica
More data?
Shard
Replica
Replica
Shard
Shard
Replica
More queries?
Replica
Replica
Replica

33. Document Routing
-How to assign documents to shards
-Default Routing
-Custom routing
-Routers
-CompositeID
-Implicit

34. Default Routing
-Each shard covers a hash-range
-Hash doc-ID into 32-bit integer, map to range
-Leads to balanced (roughly) shards

35. Default Routing
Shard 1 0 - 7fffffff
Collection
Document-1 Id = bookdoc1
Document-2 Id = magazinedoc1
Document-3 Id = bookdoc2
32 bit Hash of Document ID
Shard 2 80000000 - ffffffff
858919514
2516704228
413288864

36. Default Routing - Querying
Shard 1
Shard 2
Shard 3
Shard 4
Shard 5
Shard 6
Shard 7
Shard 8
Collection
Application
q=soccer

37. Custom Routing
-Route documents to specific shards
-based on a shard key component in the document ID

38. Custom Routing
-send documents with a prefix in the document ID
-prefix in ID will be used to calculate the hash to determine the shard
-Prefix must be separated by exclamation mark(!)
-Example:
1.Book!doc1
2.Magazine!doc1
3.Book!author!doc2

39. Custom Routing - Indexing
Shard 1 0 - 7fffffff
Collection
Document-1 Id = book!doc1
Document-2 Id = magazine!doc1
Document-3 Id = book!doc2
Shard 2 80000000 - ffffffff

40. Custom Routing - Querying
http://10.0.0.7:8983/solr/collection1/select? q=soccer& _route_=books http://10.0.0.7:8983/solr/collection1/select? q=soccer& _route_=books,magazines

41. Custom Routing - Querying
Shard 1
Shard 2
Shard 3
Shard 4
Shard 5
Shard 6
Shard 7
Shard 8
Collection
Application
q=soccer&_route_=books!

42. Implicit Router
-A field can be defined while creating collection to be used for routing http://localhost:8983/solr/admin/collections? action=CREATE& name=articles& router.name=implicit& router.field=article-type

43. Collection Aliasing
-allows you to setup a virtual collection that actually points to one or more real collections
-Virtual collection == alias localhost:8983/solr/admin/collections? action=CREATEALIAS &name=alias-name &collections=collection-list

44. Collection Aliasing
-Time-series data
June
last3months
latest
July
Aug
Sep
Oct
alias
alias
Real Collections

45. Collection Aliasing
June
last3months
latest
July
Aug
Sep
Oct
alias
alias
Real Collections
localhost:8983/solr/admin/collections? action=CREATEALIAS &name=last3months &collections=aug,sep,oct
localhost:8983/solr/admin/collections? action=CREATEALIAS &name=latest &collections=oct

46. Collection Aliasing
June
last3months
latest
July
Aug
Sep
Oct
alias
alias
Real Collections
localhost:8983/solr/admin/collections? action=CREATEALIAS &name=last3months &collections=sep,oct,nov
localhost:8983/solr/admin/collections? action=CREATEALIAS &name=latest &collections=nov
Nov

47. Collection Aliasing
-Aliases can be:
•updated on the fly
•queried just like a normal collection
•used for indexing as long as it is pointing to a single collection

48. Other Features
-Near-Real-Time Search
-Atomic Updates
-Optimistic Locking
-HTTPS
-Use HDFS for storing indexes
-Use MapReduce for building index

49. Thanks
-Attributions:
•Shalin Mangar’s slides on “SolrCloud: Searching Big Data”
•Rafał Kuć’s slides on “Scaling Solr with SolrCloud”
-Connect
•saumitra.srivastav@glassbeam.com
•saumitra.srivastav7@gmail.com
•https://www.linkedin.com/in/saumitras
•@_saumitra_
-Join:
•http://www.meetup.com/Bangalore-Apache-Solr-Lucene-Group/