Causal Consistency For Large Neo4j Clusters Jim Webber Chief - - PowerPoint PPT Presentation

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Causal Consistency For Large Neo4j Clusters Jim Webber Chief - - PowerPoint PPT Presentation

Feb 28, 2024 110 likes •1.11k views

Causal Consistency For Large Neo4j Clusters Jim Webber Chief Scientist, Neo4j QCon London Leads to a social graph Motivation Why do we need clusters of Neo4j? Massive Throughput Data Redundancy Data Redundancy Data Redundancy Data

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Causal Consistency For Large Neo4j Clusters

Jim Webber Chief Scientist, Neo4j QCon London

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Leads to a social graph

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Motivation

Why do we need clusters of Neo4j?

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Massive Throughput

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Data Redundancy

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Data Redundancy

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Data Redundancy

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Data Redundancy

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High Availability

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High Availability

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High Availability

Error! 503: Service Unavailable

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High Availability

Error! 503: Service Unavailable

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High Availability

Error! 503: Service Unavailable

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High Availability

Error! 503: Service Unavailable

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High Availability

✓

Error! 503: Service Unavailable

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Data Redundancy Massive Throughput High Availability

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Data Redundancy Massive Throughput High Availability

3.0

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Data Redundancy Massive Throughput High Availability

3.0

Bigger Clusters Consensus Commit Built-in load balancing

3.1

Causal Clustering

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Roles for safety and scale

Divide and conquer complexity

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Read Replicas Core

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  • Small group of Neo4j databases
  • Fault-tolerant Consensus Commit
  • Responsible for data safety

Core

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Writing to the Core Cluster

Neo4j Driver Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

CREATE (:User {...})

✓

Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

CREATE (:User {...})

✓

Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

CREATE (:User {...})

✓ ✓ ✓

Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

CREATE (:User {...})

✓ ✓ ✓

Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

CREATE (:User {...})

✓ ✓ ✓

Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

✓ ✓ ✓

Success Neo4j Cluster

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Writing to the Core Cluster

Neo4j Driver

✓ ✓ ✓

Success Neo4j Cluster

✓ ✓

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Raft Protocol

Non-Blocking Consensus for Humans

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Raft Protocol

https://github.com/ongardie/raftscope

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Raft in a Nutshell

  • Raft keeps logs tied together (geddit?)
  • Logs contain entries for both the database and the cluster membership
  • Entries are appended and subsequently committed if a simple majority agree
  • Implication: majority agree with the log as proposed
  • Anyone can call an election: highest term (logical clock) wins, followed by highest committed,

followed by highest appended.

  • Appended, but not committed, entries can be truncated, but this is safe (translates as transaction

aborted)

https://github.com/ongardie/raftscope

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Consensus Log → Committed Transactions → Updated Graph

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Transaction log: the same transactions appear in the same order on all members Consensus log: stores both committed and uncommitted transactions

Uncommitted entries may differ between members

Transactions are only appended to the transaction log when committed according to Raft Transactions are applied, updating the graph

Neo4j Raft implementation

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  • Small group of Neo4j databases
  • Fault-tolerant Consensus Commit
  • Responsible for data safety

Core

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  • For massive query throughput
  • Read-only replicas
  • Not involved in Consensus Commit
  • Disposable, suitable for auto-scaling

Read Replicas

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Propagating updates to the Read Replicas

Neo4j Driver Neo4j Cluster

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Propagating updates to the Read Replicas

Neo4j Driver Neo4j Cluster Write

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Propagating updates to the Read Replicas

Neo4j Driver Neo4j Cluster Write

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Reading from the Read Replicas

Neo4j Driver Neo4j Cluster Read

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Updating the graph Querying the graph

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Read Replicas Core

Updating the graph Queries, analysis, reporting

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ESTATE=$(neo-workbench estate add database -p Local -b core-block -s 3) neo-workbench estate add database -p Local -b edge-block -s 10 $ESTATE neo-workbench database install -m Core \

  • -package-uri file:///Users/jim/Downloads/neo4j-enterprise-3.1.1-unix.tar.gz \
  • b core-block $ESTATE

neo-workbench database install -m Read_Replica \

  • -package-uri file:///Users/jim/Downloads/neo4j-enterprise-3.1.1-unix.tar.gz \
  • b edge-block $ESTATE

neo-workbench database start $ESTATE

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:sysinfo

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Building an App

Computer science meets technology

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App Server Neo4j Driver Bolt protocol

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Java

<dependency> <groupId>org.neo4j.driver</groupId> <artifactId>neo4j-java-driver</artifactId> </dependency>

Python

pip install neo4j-driver

.NET

PM> Install-Package Neo4j.Driver

JavaScript

npm install neo4j-driver

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https://neo4j.com/developer/language-guides

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bolt://

GraphDatabase.driver( "bolt://aServer" )

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bolt+routing://

GraphDatabase.driver( "bolt+routing://aCoreServer" )

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GraphDatabase.driver( "bolt+routing://aCoreServer" ) Bootstrap: specify any core server to route load across the whole cluster

bolt+routing://

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Application Server Neo4j Driver

Max Jim Jane Mark

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Routed write statements

driver = GraphDatabase.driver( "bolt+routing://aCoreServer" ); try ( Session session = driver.session( AccessMode.WRITE ) ) { try ( Transaction tx = session.beginTransaction() ) { tx.run( "MERGE (user:User {userId: {userId}})", parameters( "userId", userId ) ); tx.success(); } }

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Routed read queries

driver = GraphDatabase.driver( "bolt+routing://aCoreServer" ); try ( Session session = driver.session( AccessMode.READ ) ) { try ( Transaction tx = session.beginTransaction() ) { tx.run( "MATCH (user:User {userId: {userId}})-[*]-(:Product) RETURN *", parameters( "userId", userId ) ); tx.success(); } }

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Consistency models

Can you read what you write?

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Cluster members slightly “ahead” or “behind” of each other

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If I query this server I won’t see the updates from transaction . If I query this server, I’ll see all updates from all committed transactions

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Updating the graph Querying the graph

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Register Login

You need to login in to continue your purchase!

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Register Login

You need to login in to continue your purchase!

Username: Password:

Create Account

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Register Login

You need to login in to continue your purchase!

Username:

jim_w

Password:

********

Create Account

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Register Login

You need to login in to continue your purchase!

Username: Password:

Login

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Username:

jim_w

Password:

********

Login

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Purchase

Login Successful

Try again

No account found!

Username:

jim_w

Password:

********

Login

𝙔

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Username:

jim_w

Password:

********

A few moments later...

✓

Login

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Purchase

Login Successful

Username:

jim_w

Password:

********

Login

A few moments later...

✓

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Q Why didn’t this work? A Eventual Consistency

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Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

11

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

11

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CREATE (:User)

Create Account

App Server A Driver

MATCH (:User)

Login

App Server B Driver

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CREATE (:User)

Create Account

App Server A Driver

MATCH (:User)

Login

App Server B Driver

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Bookmark

Session token String (for portability) Opaque to application Represents ultimate user’s most recent view

  • f the graph

More capabilities to come

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Let’s try again, with Causal Consistency

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Create Account

App Server A Driver

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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9

CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

11

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CREATE (:User)

Create Account

App Server A Driver

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CREATE (:User)

Create Account

App Server A Driver

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9

CREATE (:User)

Create Account

App Server A Driver

11

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9

CREATE (:User)

Create Account

App Server A Driver

MATCH (:User)

Login

App Server B Driver

11

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

CREATE (:User)

Create Account

MATCH (:User)

Login

App Server A App Server B Driver Driver

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

CREATE (:User)

Create Account

MATCH (:User)

Login

App Server A App Server B Driver Driver

11

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

CREATE (:User)

Create Account

MATCH (:User)

Login

App Server A App Server B Driver Driver

11

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Obtain bookmark

try ( Session session = driver.session( AccessMode.WRITE ) ) { try ( Transaction tx = session.beginTransaction() ) { tx.run( "CREATE (user:User {userId: {userId}, passwordHash: {passwordHash})", parameters( "userId", userId, "passwordHash", passwordHash ) ); tx.success(); } String bookmark = session.lastBookmark(); }

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CREATE (:User)

Create Account

MATCH (:User)

Login

App Server A App Server B Driver Driver

11

Obtain bookmark

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Use a bookmark

try ( Session session = driver.session( AccessMode.READ ) ) { try ( Transaction tx = session.beginTransaction( bookmark ) ) { tx.run( "MATCH (user:User {userId: {userId}}) RETURN *", parameters( "userId", userId ) ); tx.success(); } }

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1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10

CREATE (:User)

Create Account

MATCH (:User)

Login

App Server A App Server B Driver Driver

11

Use bookmark

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Read Replicas Core

Updating the graph Queries, analysis, reporting

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Thank you for listening

@jimwebber