Apache Solr is a highly scalable search platform with over 250,000 installations and remarkable features including support for large index sizes, distributed indexing, and replicas for high availability. SolrCloud enhances scalability and performance by enabling horizontal scaling through sharding and replication, while utilizing Zookeeper for centralized management and coordination. Key functionalities of Solr include near-real-time search, partial document updates, and transaction logs for improved recoverability.

1. Introduction To SolrCloud
Varun Thacker

2. Apache Solr has a huge install base and tremendous momentum
Solr is both established & growing
250,000+
most widely used search
solution on the planet. 8M+ total downloads
monthly downloads
You use Solr everyday.
Solr has tens of thousands
of applications in production.
2500+ open Solr jobs.
Activity Summary
30 Day summary
Aug 18 - Sep 17 2014
• 128 Commits
• 18 Contributors
12 Month Summary
Sep 17, 2013 - Sep 17, 2014
• 1351 Commits
• 29 Contributors
via https://www.openhub.net/p/solr

3. Solr scalability is unmatched.
• 10TB+ Index Size
• 10 Billion+ Documents
• 100 Million+ Daily Requests

4. Solr’s scalability is unmatched

5. What is Solr?
• A system built to search text
• A specialized type of database management
system
• A platform to build search applications on
• Customizable, open source software

6. Where does Solr fit?

7. What is SolrCloud?
Subset of optional features in Solr to enable and
simplify horizontal scaling a search index using
sharding and replication.
Goals
scalability, performance, high-availability,
simplicity, and elasticity

8. Terminology
• ZooKeeper: Distributed coordination service that provides centralised
configuration, cluster state management, and leader election
• Node: JVM process bound to a specific port on a machine
• Collection: Search index distributed across multiple nodes with same
configuration
• Shard: Logical slice of a collection; each shard has a name, hash range, leader
and replication factor. Documents are assigned to one and only one shard
per collection using a hash-based document routing strategy
• Replica: A copy of a shard in a collection
• Overseer: A special node that executes cluster administration commands and
writes updated state to ZooKeeper. Automatic failover and leader election.

10. Collection == Distributed Index
• A collection is a distributed index defined by:
• named configuration stored in ZooKeeper
• number of shards: documents are distributed across N partitions of the index
• document routing strategy: how documents get assigned to shards
• replication factor: how many copies of each document in the collection
• Collections API:
• curl "http://localhost:8983/solr/admin/collections?
action=CREATE&name=punemeetup&replicationFactor=2&numShards=2&coll
ection.configName=myonf

11. DEMO

12. Document Routing
• Each shard covers a hash-range
• Default: Hash ID into 32-bit integer, map to range
• leads to balanced (roughly) shards
• Custom-hashing
• Tri-level: app!user!doc
• Implicit: no hash-range set for shards

13. 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

14. Distributed Indexing
• Get cluster state from ZK
• Route document directly to leader (hash on doc ID)
• Persist document on durable storage (tlog)
• Forward to healthy replicas
• Acknowledge write succeed to client

15. Shard Leader
• Additional responsibilities during indexing only!
Not a master node
• Leader is a replica (handles queries)
• Accepts update requests for the shard
• Increments the _version_ on the new or updated
doc
• Sends updates (in parallel) to all replicas

16. Distributed Queries
• 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

17. Scalability / Stability Highlights
• All nodes in cluster perform indexing and execute
queries; no master node
• Distributed indexing: No SPoF, high throughput via
direct updates to leaders, automated failover to new
leader
• Distributed queries: Add replicas to scale-out qps;
parallelize complex query computations; fault-tolerance
• Indexing / queries continue so long as there is 1 healthy
replica per shard

18. Zookeeper
• Is a very good thing ... clusters are a zoo!
• Centralized configuration management
• Cluster state management
• Leader election (shard leader and overseer)
• Overseer distributed work queue
• Live Nodes
• Ephemeral znodes used to signal a server is gone
• Needs 3 nodes for quorum in production

19. Zookeeper: State Management
• Keep track of live nodes /live_nodes znode
• ephemeral nodes
• ZooKeeper client timeout
• Collection metadata and replica state in /clusterstate.json
• Every core has watchers for /live_nodes and /
clusterstate.json
• Leader election
• ZooKeeper sequence number on ephemeral znodes

20. Other Features/Highlights
• Near-Real-Time Search: Documents are visible within a second or so after
being indexed
• Partial Document Update: Just update the fields you need to change on
existing documents
• Optimistic Locking: Ensure updates are applied to the correct version of a
document
• Transaction log: Better recoverability; peer-sync between nodes after
hiccups
• HTTPS
• Use HDFS for storing indexes
• Use MapReduce for building index (SOLR-1301)

21. Solr on YARN

22. Solr on YARN
• Run the SolrClient application :
• Allocate container to run SolrMaster
• SolrMaster requests containers to run SolrCloud
nodes
• Solr containers allocated across cluster
• SolrCloud node connects to ZooKeeper

23. More Information on Solr on YARN
• https://lucidworks.com/blog/solr-yarn/
• https://github.com/LucidWorks/yarn-proto
• https://issues.apache.org/jira/browse/SOLR-6743

24. Our users are also pushing the limits
https://twitter.com/bretthoerner/status/476830302430437376

25. Up, up and away!
https://twitter.com/bretthoerner/status/476838275106091008

26. Connect @
https://twitter.com/varunthacker
http://in.linkedin.com/in/varunthacker
varun.thacker@lucidworks.com