On ReplicationOn Replication

July 2006July 2006Yin ChenYin Chen

• What is? Why need? Types?• Investigation of existing technologies

– IBM SQL replication– Sybase replication– Oracle replication– MySQL replication– Globus DRS– EGEE RMS– SRB

• Our project– Goals– Solutions– Features

OverviewOverview

• Copying of data & synchronization of updating

• Is not Cashing – Client phenomenon– Only for improving response time

• Is not a Backup (not automatically overwritten when the original data is modified )

• Is not a replicated system– deal with when/where to copy– Optimization (how much replica needed …)– Grow or shrink replication tree

What is replication?What is replication?

• Data consolidation (central audit & analyse)• Data distribution (for branch offices)• Performance

– Access efficiency (moving data near apps.)– Load balance (distributing access load)– Security (data protection)– Availability (off-line access)– Reliability (disaster recovery, avoiding single

point of failure)• Data Grid (to improve availability, response

time, fault tolerance)• Digital Library (copying digital doc, index … )

Why we need it?Why we need it?

• Synchronous Replication: What is: updating two storages at the same time; roll

back if one fails Benefits: High availability/auto fail-over/minimal data lossUsages: Disaster recoverDrawbacks: Network efficiency /scalability/cost/less

flexibility

• Asynchronous Replication: What is: changes are captured on the primary storage

and immediately / timely propagatedBenefits: low cost / scalability /flexibilityUsages: load balance/off-line access/access efficiencyDrawbacks: data lost / network bandwidth

Replication typesReplication types

Existing Existing technologiestechnologies

IBM Replication

WebSphere Information Integrator V8.2

Supports multivendors DB

Admin: create replication criteria control table

Capture: use log/trigger to capture the changes temp table

Apply: scheduled apply transactions accumulated target DB

Alert Monitor: monitor and notify users

Supports: after-image copy / before-image copy (can rollback)

Allows subset/simple view/ complex joins & unions copy

Asynchronous replication, allows specifying schedule

IBM Replication

Sybase Replication

Pioneer, Since 1993

“publish-and-subscribe” approach

Replication Agent: runs on each publisher, detects changes base on logs

Replication Server: apply changes to target DBs (use pre-configured intelligent routes)

Replication Server Manager: GUI-based, manage/monitor P2P env.

Stable Queues: temporary storage of data , ensure no data is lost

Is advanced in providing high performance

Sybase Replication

Oracle Replications

Multimaster Replication Materialized View Replication Multimaster Replication

P2P structure

Changes are pushed to every other site (synchronous/ asynchronous)

Conflicts may happen (Update conflict/Uniqueness conflict /Delete conflict )

Materialized View Replication

One master site manages several non-master sites (keep one/partial copy)

Updatable

Refresh (fast refresh/ complete refresh/ force refresh)

Hybrid Replication

Oracle Replications

MySQL Replications

1. simple master/slaver

3. dual masters

2. one slave two masters

4. dual master with slaves5. master ring 6. master ring with slaves

MySQL Replications

Basic replication services, using a light weight Master-Slave model

The master writes updates to logs; the slave reads and executes the queries from the master’s logs

the slave checks results on both sites, replication stops if query only succeeds on one site

This simple structure can be combined arbitrarily to build complex architectures

In a slow network, it is difficult for a slave to catch up with the master – improved in 4.0 by adding relay logs

Have to lock or restart the master for initial snapshot copy

Existing Existing technologiestechnologies

Globus DRS

Globus DRS

A client creates a request file (requested file name & target location) and sends to DRS

The Replicator checks user’s credential, and query RLI to find the LRC that contain mappings for the requested file

Also queries each remote LRC to get the physical file names, and selects a best one

Then starts RFT to transfer files.

Finally, registers the new replica to its LRC. The LRC will updates LRI to make replica visible

Existing Existing technologiestechnologies

EGEE RMS

Designed for large, read-only, file replicating among heterogeneous resources

Implement File Catalogues

Replica Location Service maps replica’s Grid Unique ID to physical location

Local Replica Catalogues provides information of replicas for a single VO

Replica Metadata Catalogue maps file’s logical name to Grid Unique ID

LCG File Catalogue is used for performance issues

EGEE RMS

Existing Existing technologiestechnologiesApplication

DISPATCHER: monitors input port and dispatches requests to handler

High Level Request Handler

MCAT

Remote SRB

Low Level Request Handler

File system driversUnitree HPSS UNIX

DBMS driversDB2 Oracle ObjectStore Illustra

SRB

Enables file searching by attributes

MCAT a database system storing metadata

one or more Master daemon processes having SRB Agent running on them

The dispatcher monitors incoming requests and pass to HLRH (can retrieve metadata from local/remote MCAT) or LLRH (can retrieve data from storage)

supports synch/asynch replication, MCAT replication

• Combining DB2 SQL Replication with OGSA-DAI technologies

• Grid-enabling DB2 Replication to provide a grid service interface for managing replication.

• Supporting more scalable, secure, high performance data access

• Extend OGSA-DAI to provide more powerful capabilities.

• Explore metadata technologies

Our GoalsOur Goals

System architectureSystem architecture

Metadata Catalogue

Relational Database Replication Mechanism

ReplicationControl Service

GridFTP Transfer

Data Resource

Data Replica

WorkflowsWorkflows

Request

Replication Control Service

MetadataSearchEngine

Metadata Register

Initiator

Selector

Starter

Metadata Catalogue

Relational Database Replication Mechanism

GridFTP Transfer

Data Resource

ReplicationTarget

FeaturesFeatures

• Keeping the features of relational database replication

• Adding Grid’s features

• Using Grid service discovery mechanism

• Supporting more replication scenarios

• Introduction of replication• Introduction of existing technologies

– Relational database replications are advanced in flexibility, offering solutions for frequent updating, update everywhere, data conflictions…

– Grid file replications are good at scalable, secure, and efficient file transferring

• We studied both model and combine the two structures to gain benefits from both

SummarySummary