The document discusses using Apache Cassandra as the distributed database for Gerrit to address challenges of distributed storage, replication, concurrent updates and cache consistency. It proposes using Cassandra to store Git pack and pack list data with specific schema. The goal is to allow all Gerrit masters to accept writes, increase throughput and flexibility while ensuring zero downtime and data loss through auto-scaling. Challenges of distributed agreement and shared sessions are also discussed.

1. Haithem Jarraya
GerritForge
Haithem@gerritforge.com
http://www.gerritforge.com
Infinite Gerrit

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About Haithem
• Haithem Jarraya
Big Data consultant based in London, worked in different
industries telecommunication, advertisement, financial services,
travel and government.
• Expertise with real time big data ecosystem, Apache Kafka,
Apache Cassandra, Apache Spark.

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About GerritForge
Founded in 2009 in London UK
Mission:
Integrate Gerrit with
the Enterprise

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Agenda
 Vision for Infinite Gerrit
 Why Cassandra?
 DfsObjDatabase – Cassandra proposed schema
• Pack list
• Packs

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Gerrit – End Goal
 Every Gerrit mater accepts writes which in
turn will increase throughput.
 Increase flexibility for scaling up.
 Zero down time, Zero data loss.
 Reduce Gerrit operational cost by auto
scaling down instances.

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Gerrit – Challenges
 Distributed storage
 Database replication
 Concurrent Ref updates
 Indexes update
 Cache consistency
 Shared sessions
 Agreement protocol between nodes

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Gerrit – Challenges
 Distributed storage
 Database replication
 Concurrent Ref updates
 Indexes update
 Cache consistency
 Shared sessions
 Agreement protocol between nodes

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C* in brief
 Each table has its rows distributed N token ranges, and each token range replicated
R times.
 Fast writes commit log(durable writes), memtable, stored to SSTable.
 Fast reads bloom filter, row key cache, row cache, SSTable index entry.
 Compaction, repairs, materialized view(3.X)…

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DFS – Storage Layer for JGit
 org...storage.dfs.DfsObjDatabase
 org….storage.dfs.DfsRefDatabase

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Packs C* schema - Packs
 Packs
CREATE TABLE git_store.packs (
id uuid,
ext text,
offset bigint,
value blob,
PRIMARY KEY ((id, ext, offset)))

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Packs C* schema – Pack list
 Pack list
CREATE TABLE git_store.pack_list (
name text,
id uuid,
ext text,
size bigint,
PRIMARY KEY (name, id, ext))
WITH CLUSTERING ORDER BY
(id DESC, ext ASC)

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LWB – HTTP route per repo

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Questions?

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Resources
 http://cassandra.apache.org
 http://www.datastax.com
 http://eclipse.org/jgit
 Dynamo paper http://s3.amazonaws.com/AllThingsDistributed/sosp/amazon-dynamo-sosp2007.pdf
 Big Table paper http://static.googleusercontent.com/media/research.google.com/en//archive/bigtable-osdi06.pdf