Assumption : Critical Systems require zero or very low downtime
Object: To migrate the databases to higher versions or from one Database to different with zero or low downtime
Introduction : database migrations means migrating/moving/porting databases from one OS to other OS, for instance,
from Windows Based Systems to UNIX Systems or vice versa or from One Unix flavour to another.
For Instance there is requirement to move Databases from Solaris or AIX to LINUX or from LINUX based systems to AIX or HP Unix.
Database migrations may also mean to migrate the databases from legacy Systems to Oracle Database or from MYSQL to DB2.
It all depends on typical customer requirements or Businees needs.
We are focussing on techniques to migrate the database on critical systems which require zero or minimal downtime.
Often the customer, having 24X7X365 Business or trasaction support cannot afford to down its systems for even a very short duration.
Examples:
It goes without saying that, the client wants minimal downtime.
As in a quintessential example in cross platform Database Migrations:
it will be clear with minimal analysis that most time-consuming operation would be the restore and recovery into the new instance.
Usually We are basically doing a restore and recovery from production backups and archived redo logs.
However, as an innovation, it can be seen that that we could start this operation well before the scheduled cutover time and downtime window, reducing by atleast a few hours (may be 5 - 8) from the downtime window.
The client requirement is just to keep the new instance in mount mode after the initial restore/recovery is finished. Periodically re-catalog the source instance’s Flash Recovery Area, and then re-run the recover database command i n RMAN. Once the time comes to cutover, simply archivelog current the original instance and shutdown immediate.
Then open the new instance with the RESETLOGS option, and the database migration completes with a very low downtime.
Database Migrations Mean, one or more of :
Migrating/moving/porting databases from one OS to other OS
Physical Movement/Relocating of Database Files from Source to Target Location
Porting to a new DB, say, frim INGRES to ORACLE
Mere transporting to a different Hardware, Software versions being the same.
Why DB Migration?
Typical customer requirements or Businees needs entail DB migration
Exponential growth of DB has out-grown the Hardware capacity
Replacement of Legacy or old systems
Reduciotn in cost of operations
New Application Functionality/characteristics works on Different DBMS
Whatis Critical DB Migration?
Often the customer, having 24X7X365 Business or trasaction support cannot afford to down its systems for even a very short duration
Often such companies may be having a business of $$$...s per hour. They cannot afford downtime.
Reputaional Risks invlovled for a downtime on a reputed Business
Operational Risks on some Mission Critical Applications
Acheiving Critical Database Migrations
The primary goal of this work is to increase awareness about solutions that eliminate/bring-to-near-zero Application
downtime during database migrations
Oracle Goldengate Solution is one solution that helps to achieve this goal
Oracle GoldenGate provides guaranteed data capture, routing, transformation, and delivery across heterogeneous business systems
Oracle-to-Oracle Migrations can also achieve this goal using streams technology
Using Standby Database
Scenario:
Migrate DB having 2K Blocksize to 8K Blocksze
Creating a temp logical standby
Re-create DB with Changed Block-size
EXP/IMP While Production is up and running on Primary site
Switchover from Primary to Standby
Critical Migrations using Goldengate
Oracle GoldenGate is a real-time change data capture application that provides guaranteed :
data capture
routing
transformation
delivery across heterogeneous business systems.
Data Capture & delivery
Oracle GoldenGate captures and delivers real-time change data to :
data warehouses
operational data stores
reporting systems
other online transaction processing (OLTP) databases
with minimal performance impact.
This access to real-time information enables improved business insight.
Goldengate Transactional Data Management (TDM) offers:
Minimal impact and Hi availability to Mission Critical Applications
Technology solution for eliminating database downtime
Improved capabilities for data integrity, accuracy & Precision
Fallback solution in the event of unexpected issues/errors
Proven – with Production Databases
GoldenGate Major Customer Examples -- This data Adapted from an Oracle site for reference
Database and/or Platform Migrations in all-Oracle environments:
Overstock.com: Oracle 9i on Linux -> Oracle 10g on AIX
HP internal testing: Oracle 9i on HP Tru64 -> Oracle 9i on HP UX
Cerner’s Millennium Application: Oracle 9i on OpenVMS -> Oracle 10g on HP UX or AIX
Migrations from non-Oracle to Oracle database environments:
Sabre Holdings: HP Nonstop -> Oracle
Siebel on Demand: IBM DB2 -> Oracle
Integrating non-Oracle data into Oracle BI systems:
Dell: OLTP on HP NonStop -> Oracle Data Warehouse
AMD: IBM DB2 -> Oracle reporting database
Seting customer Expectaions
Understand the Customer Requirement and Develop an Extensive Technical Project Plan
Explain the Project Plan to Customer
The Project work starts well before the Production cut-over
Expectations about the downtime
Risks and Fallback
Yet Another Example with Near Zero Downtime
Another approach where Application requires extensive testing on a new environement
Build Standby Databases
Import the data utilizing RMAN Convert if required
Using Streams/Goldengate to enable Replication
Start Application Testing
Flashback Database to the point Immediately Prior to Testing
Check Whether Target is in Sync
Cutover to Target Database
More on Flashback, Streams and Rman Convert
Flashback Teachnology is required when extensive testing is essential for mission critical Applications
Different Testing needs to be conducted at all levels -- Unit, System & Integration
Extensive testing of datacenter infrastructure & database LPAR performance before go-live
Streams Replication can be installed to propogate all transaction to reduce downtime
