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On Replication Yin Chen July 2006 Overview • 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 What is replication? • 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 Why we need it? • 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 … ) Replication types • Synchronous Replication: What is: updating two storages at the same time; roll back if one fails Benefits: High availability/auto fail-over/minimal data loss Usages: Disaster recover Drawbacks: Network efficiency /scalability/cost/less flexibility • Asynchronous Replication: What is: changes are captured on the primary storage and immediately / timely propagated Benefits: low cost / scalability /flexibility Usages: load balance/off-line access/access efficiency Drawbacks: data lost / network bandwidth Existing technologies WebSphere Information Integrator V8.2 Supports multivendors DB IBM Replication Admin: create replication criteria control table Capture: use log/trigger to capture the changes temp table IBM Replication 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 Pioneer, Since 1993 “publish-and-subscribe” approach Sybase Replication Replication Agent: runs on each publisher, detects changes base on logs Sybase Replication 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 Multimaster Replication Multimaster Replication P2P structure Materialized View Replication Oracle Replications Oracle Replications 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 3. dual masters Basic replication services, using a light weight Master-Slave model 1. simple master/slaver 2. one slave two masters 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 relayring logs 5. master 6. master ring with slaves 4. dual master with slaves Have to lock or restart the master for initial snapshot copy MySQL Replications MySQL Replications Globus DRS Existing technologies 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 Globus DRS Existing technologies 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 EGEE RMS LCG File Catalogue is used for performance issues EGEE RMS Existing technologies Application DISPATCHER: monitors input port and dispatches requests to handler Enables file searching by attributes MCAT High Level MCAT a database system storing metadata Request Handler one or more Master daemon processes having SRB Remote SRB Agent running on them The dispatcher monitors incoming requests and pass to HLRH (can retrieve metadata from Low Level Request Handler MCAT) or LLRH (can retrieve data from local/remote DBMS drivers File system drivers storage) DB2 Oracle Unitree HPSS ObjectStore Illustra supports synch/asynch replication, MCAT UNIX replication SRB Our Goals • Combining DB2 SQL Replication with OGSADAI 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 System architecture GridFTP Transfer Metadata Catalogue Data Resource Replication Control Service Relational Database Replication Mechanism Data Replica Workflows Request Replication Control Service Metadata Search Engine Initiator GridFTP Transfer Starter Relational Database Replication Mechanism Data Resource Metadata Catalogue Selector Metadata Register Replication Target Features • Keeping the features of relational database replication • Adding Grid’s features • Using Grid service discovery mechanism • Supporting more replication scenarios Summary • 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