Download 5_Database Back up

Database recovery contd…
10. 03 . 2011
• RECAP
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RECAP
Database Backup
• Causes of failure:
– Transaction failure
– System/processor failure
– Media failure
• When secondary media (disk) fails, data may become unreadable.
• We typically rely on backing up the database to cheaper magnetic
tape or other backup medium for a copy that can be restored.
• Challenge:
– When an DBMS is running, it is not possible to backup its files (data
files, system logs, redo logs, etc.) as the resulting backup copy on tape
may be inconsistent.
• “old practice”:
– Shut down the DBMS (and thus all applications), do a full backup, copy
everything on to tape. Then start up again.
• Types of back up
– Logical (Hot or Cold)
• Export facility
– Physical (with or without a Recovery manager)
• File system and SQL statements back up
– Incremental versus full back up
Other than data, Other parts of the database to be
backed up include the log files and any control
files that monitor the state of the database
• Incremental
– An Incremental backup will backup only those
data changed or added since the last full backup.
Sometimes called a delta backup.
• Follows something like:
– Weekend: Do a shutdown of the DBMS, and full
backup of the database onto a fresh tape(s).
– Nightly: Do an incremental backup onto different
tapes for each night of the week.
• Please see Database Backup Examples from
the notes
– MS Access
– Microsoft SQL Server
– Oracle
• Discussion slides
• Scenario:
– You are a new hiring at a company – you realize
that there isn’t a database back up strategy in
place. What do you do?
Advisory note to your superior / ICT director
may include/highlight:
– Objectives of DB backup
– Uses of a DB back up
– Information of how to develop a back up and
recovery strategy
Advisory note to your superior / ICT director
may include/highlight:
• Objectives of DB backup
– Protect the database from numerous types of
failures
– Increase Mean-Time-Between-Failures (MTBF)
– Decrease Mean-Time-To-Recover (MTTR)
– Minimize data loss
• A database backup will enable:
– Archive historical data
– Save table definitions (with or without data) to
protect from user error failure
– Move data between machines and databases or
versions of a server (e.g. Oracle server)
– Transport tablespaces between databases
Normally in
binary formats
Data
Base
Exp
Data
Base
Imp
File *.dmp
• Steps in developing a back up and recovery
strategy
– Identify the business requirements
• E.g. Evolutionary process
– Identify technical requirements
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Hardware, software, man power and time
Database configurations
Transaction volume
Frequency of backups
– Define operational requirements
• 7-day / 24-hour operations
• Testing and validating backups
• Back up and recovery strategy considerations
– Identify critical data from the rest
– Assess tolerance for data loss - Recovery Point
Objective (RPO)
– Assess tolerance for downtime - Recovery Time
Objective (RTO)
– Determine backup retention policy
– Assess data protection requirements
What are example questions that you can
raise for each consideration?
• Back up and recovery strategy considerations
– Identify critical data from rest
• Design recovery requirements around data criticality
– Assess tolerance for data loss - Recovery Point
Objective (RPO)
• How frequently should backups be taken?
• Point-in-time recovery required?
– Assess tolerance for downtime - Recovery Time
Objective (RTO)
• Downtime: Problem identification + recovery planning +
systems recovery
• Tiered RTO per level of granularity, e.g. database,
tablespace, table, row
• Backup and recovery strategy considerations
– Determine backup retention policy
• Onsite, offsite, long-term
– Assess data protection requirements
• Physical: Disasters, outages, failures, corruptions
• Logical: Human errors, application errors
Your homework!
• Home work / self research
– Form groups for research
– In your group, research and report in the next class what
the following DBMSs in the market address recovery
1.
2.
3.
4.
5.
MS Access
Oracle
MS SQL (Server)
MySQL
PostgreSQL
Due next week (a small write up + 5minutes presentation)
After the written CAT
• Thanks