Clustering

1
Clustering

• Types of Clustering

2
Objectives

• At the end of this module the student will
  understand the following tasks and concepts.
• What clustering is and why you would want it
• Clustering options
• Differences between various types of clustering
  advantages and disadvantages
• Factors to consider when choosing a cluster type

3
What is a cluster?

• My definition
• Multiple systems performing a single function
• Black box

4
Why Cluster?

• Performance
• Availability
• Recoverability

5
Features

• Speedup
• Faster response times
• Transactions finish faster
• Scaleup
• More work done
• More capacity, more concurrent transactions
• Scalability

6
Single Node Scaling

• Scales to multiple CPUs
• Doesnt scale beyond one node
• Multiple single points of failure

Users
Database
Database
7
Cluster Definitions

• Shared Nothing (Federated)
• Replicated Site
• Shared Disk
• Failover
• Active/Passive
• Active/Active
• Shared Everything

8
Shared Nothing Cluster

• Only one CPU is connected to a disk
• May have shared memory
• MPP Systems are Shared Nothing
• Other vendors have Shared Nothing clusters

9
Federated (Shared Nothing) Cluster

• Distributed database (separate database on each
  machine)
• Data is spread across nodes each machine has
  part of the data
• Function is spread across nodes
• Two-Phase Commit

Got it?
1.
Good!
3.
Got it!
2.
Database
Database
10
Replicated System

• Data replicated at the server (network) level or
  at the storage (SAN) level
• Multiple copies of the same database
• Most common implementation is Active/Passive
• Failover between nodes

Passive Node
Active Node
Server level Replication
or
Storage level Replication
Database
Database
11
Shared Disk Cluster

• Shared file system
• Multiple systems attached to the same disk
• All nodes must have access to data
• Only one database instance only one node has
  ownership of the shared disk
• Synchronization between systems If one node
  fails, then the other takes over

12
Cluster Interconnect

• Most Shared Disk clusters require some form of
  Cluster Interconnect
• Network i.e. Gigabit Ethernet
• Specialized i.e. Infiniband, Myrinet
• Most clusters implement a heartbeat between
  cluster nodes to monitor node health
• Multiple nodes require a switch
• Usually separated from the LAN
• Some shared disk clusters implement a heartbeat
  mechanism to a quorum disk via the SAN in
  addition to/instead of network heartbeat
• Oracle RAC implements Cache Fusion across the
  interconnect
• Extra network traffic increases the throughput
  requirements
• UDP implementation requires a separate network

13
Failover Cluster

• One system is a standby system for another
• Only one system doing work at a time
• Pseudo-Shared Disk
• Limited scalability in active/passive mode

14
Failover Clustering
Users

• Fault tolerant systems highly available
• Basic failover clusters dont scale beyond two
  nodes

Database
Database
15
Active/Passive vs. Active/Active

• Both are failover only
• Active/Passive
• One node is active
• The other is passive until failover
• Active/Active
• Still uses active/passive technology
• 2 separate databases
• One is active on node A and passive on node B
• The second database is active on node B and
  passive on node A.
• Separate applications and user connections to
  each of the different databases

16
Active/Passive
Node A
Node B

• Node A is active
• Node B is passive until/unless Node A fails
• Only one Oracle license is required

17
Active/Passive
X
Node A
Node B
If Node A fails
18
Active/Passive
X
Node A
Node B

• Node B becomes active
• Node A is dead (definitely passive!) until
  repaired and then failed back if necessary.

19
Active/Active

• Application Group A and User Group A are active
  on Node A
• Application Group B and User Group B are active
  on Node B
• Each node serves as failover for the other.
• 2 separate databases. Both nodes are not
  accessing the same data at the same time.
• Oracle license required on each node

Node A
Node B


Application A User Group A
Application B User Group B
Passive Fail-over for B
Passive Fail-over for A
20
Switchover vs. Failover

• Many cluster systems utilize the concept of
  Service Groups
• Service Groups allow granular control of
  individual software packages (i.e. individual
  Oracle instances)
• An individual group can be manually moved to
  another server without affecting other service
  groups a switchover versus a failover
• Adds greater management flexibility

21
N-to-1 Failover Configuration

• Node D is a dedicated failover node for failures
  on Node A, B, and C
• Extends number of active nodes
• A problem is that once the failed node is
  available, the Service Groups on Node D (failover
  node) must failback to original server to restore
  High Availability

22
N 1 Failover Configuration
Node A
Node B
Node C
Node D

• Node D is a dedicated failover node for failures
  on Node A, B, and C
• Extends number of active nodes
• Once Node C is restored, it becomes the failover
  node, leaving Node D in production.

Failover




Application A User Group A
Application D User Group D
Application G User Group G
Failover G
X




Application B User Group B
Application E User Group E
Application H User Group H
Failover H
Application C User Group C
Application F User Group F
Application I User Group I
Failover I
23
N-to-N Failover Configuration
Node A
Node B
Node C
Node D

• Node C fails, and its Service Groups are
  re-distributed across surviving nodes
• Optimal solution for gt 2 nodes
• Implemented on third party failover clusters and
  Oracle RAC

Failover G
Failover H
Failover I




Application A User Group A
Application D User Group D
Application G User Group G
Application J User Group J
X




Application B User Group B
Application E User Group E
Application H User Group H
Application K User Group K
Application C User Group C
Application F User Group F
Application I User Group I
Application L User Group L
24
Third Party Clusters

• Support for extended cluster nodes up to 32
  nodes for vendor Clustering
• Supports N 1 and N - N failover clustering
• Integrated with hardware and/or software
  replication for long distance clusters

25
Clustering Solutions from Oracle

• Oracle Failsafe
• Oracle Data Guard
• Advanced Replication
• Shared Nothing Cluster
• Oracle Parallel Server
• Real Application Clustering (RAC)

26
Failsafe

• MS Clustering Enabled
• Two servers one disk subsystem
• Switches in the event of a hardware failure
• Requires recovery

27
Standby Database

• Copy of Database (usually remote)
• Kept up to date with Archive Logs
• Oracle 8i feature
• Oracle 9i-10g version of a standby database is
  Data Guard

28
Oracle Data Guard

• Mirrored Server
• Physical Standby
• Archive Logs are applied to the remote database
• Switchover occurs in the event of a failure
• Logical Standby
• Log Miner technology is used to generate SQL
• Standby Database can also be used for read-only
  reporting
• Advantages
• Safe from user failure
• Can be in different location
• No recovery required

29
Advanced Replication

• Uses Updatable-Snapshots
• Replicates to another system
• Systems stay in sync

30
Oracle Parallel Server

• Shared disk cluster product
• Loosely Coupled
• Scalable performance
• No downtime in the event of a system failure
• Replaced by RAC in 9i

31
True Shared Disk Server (RAC)

• ONE database
• Separate multiple instances (processes memory)
• All nodes can access data simultaneously
• Shared Everything Cluster
• Transparent Application Failover
• Oracle license required on each node
• Highest level of cluster functionality

Node A
Node B
32
Factors to Consider for Clustering

• Which do you need most?
• High Availability Failover Clusters,
  Synchronous Replication, Data Guard
• Performance scalability Active/Active failover
  clusters, N-to-N failover clusters
• Both Oracle RAC
• Administration complexity
• Failover clusters relatively low
• Oracle RAC relatively high
• Substantially less complex for 10g RAC than 9i
  RAC
• Local or long distance?
• Local Failover, RAC
• Remote Federated database, Replication, Standby
  database/Data Guard
• Oracle license costs
• Active/Passive failover clusters active nodes
  only
• Active/Active failover clusters, RAC per node

33
Review

• What type of commit is required for a Federated
  (shared nothing) cluster?
• What is the difference in how the database is
  kept up-to-date in Oracle Data Guard vs. Advanced
  Replication?
• What is the difference between N-to-1 failover
  clusters and N 1 failover clusters?
• How many databases are there in an 8 node Oracle
  RAC cluster?

34
Summary

• Types of clusters
• Shared Nothing Clusters
• Federated databases
• Replication
• Shared Disk Clusters
• Failover
• Oracle RAC
• Failover Clusters
• Active/Passive
• Active/Active
• N-to-1
• N 1
• N-to-N
• Shared Everything Clusters
• Oracle RAC
• Choosing a cluster type involves trade-offs in
  functionality, costs, and administration
  complexity