1. Week 7 : Chapter 7 Agenda SQL 710 Maintenance Plan:
Why do maintenance?
Overview
Maintenance Plan wizard
DBCC maintenance commands
SQL 710

2. Why do Maintenance?
Routinely want to make a backup copy of database in case of hardware problems or data corruption
Data in a database becomes fragmented over time as data is added, modified and deleted
Should verify integrity of data occasionally
Normally want to perform these tasks when you choose – not as the result of a crisis (just like car maintenance; don’t want to be stuck on the side of a highway with no oil in engine)!
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3. Maintenance Overview SQL 710 Day-to-day operation
Very important responsibility of a DBA
If you do maintenance nobody notices but if you don’t do it everyone knows
2 types of maintenance:
- to keep database running  most important
- to improve performance
Database maintenance can be fully automated – there is a wizard for almost every task
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4. Database Maintenance Wizard
Primary tool for database maintenance
Graphical tool
Can create a scheduled maintenance plan for each database that performs:
Backups (most important!)
Optimization
Integrity Check
Reporting
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5. Maintenance Planning SQL 710
Normally use wizard to create a maintenance plan for each database
Best to have one plan per database but can choose more than 1 database per plan
Plans are scheduled separately as required by application
Very important to create a separate maintenance plan for critical system databases: master, msdb
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6. Maintenance Plan
A Maintenance Plan consists of a group of jobs and schedules called a plan
A plan can be edited after you create it
Very simple tool to use - no excuse not to use it
Within a job you can perform:
Backups
Optimization
Integrity Check
Reporting
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7. Database Backups
Most important part of maintenance plan: permits recovery of data from backup copy
Backs up database files or logs to a tape or hard drive
Hard drive location can be broken into several directories for each database
Can automatically delete older backups after a certain time
Wizard records all activities and sends notification
Report can be sent to disk, a central server, a history table or to an operator
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8. Optimization SQL 710 Improves database performance
Database gets fragmented when data is inserted and deleted (same as files on a hard drive, see last slides for illustration)
Optimization causes the following to be performed that can improve database performance:
Examine and minimize fragmentation of data
Update database statistics
Remove excess free space from database
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9. Data Fragmentation SQL 710
Database get fragmented when data is inserted or deleted
You can select how much free space for new data will be left when defragmenting is done
If database is primarily for data entry (OLTP) then it is best to leave significant free space at the end of each page so that related data stays together
If database is composed of data that is read more often than being written (OLAP) such as a report server then leave lower percentage of page space free.
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10. Update database statistics
Statistics are samples of data used to assist SQL Server search engine in locating data
As data is added and deleted these statistics become outdated
Can keep statistics updated 2 ways:
Use wizard to schedule update of statistics periodically (this may slow performance if statistics are out of date because data would not be retrieved efficiently)
Set database option that automatically updates statistics (this slows performance because statistics are continually updated)
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11. Remove excess free space
This setting in the wizard permits shrinking the database at a specific recurring time.
Automatic shrink of database can be set as an option
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12. Database Integrity Check
SQL Server is a very stable RDBMS
However should check integrity of a database periodically
Integrity checks validity of defined database constraints (NN, PK, FK, CK, UN)
Integrity check can correct minor errors automatically
May have to restore data from backup if major integrity error is found (very rare!)
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13. T-SQL Maintenance Commands
T-SQL maintenance commands are the Database Consistency Check commands (DBCC)
Command line utility
Maintenance wizard actually uses these commands
Perform maintenance on Database Index and file groups
Commands include:
DBCC CHECKDB
DBCC CHECKTABLE
DBCC DBREINDEX
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14. SQL 710 DBCC CHECKDB Command
CHECKDB command examines an entire database for corruption (checks all tables and indexes in database)
Command can be run in diagnostic mode
To correct any problem it has to be run in single user mode
Can use REPAIR_FAST or
REPAIR_ALLOW_DATA_LOSS switch
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15. CHECKDB Switches SQL 710 REPAIR_FAST Switch:
Least amount of damage to database
Quickly fixes any inconsistency
Don’t lose any data
REPAIR_ALLOW_DATA_LOSS Switch:
Most harmful switch but could save overall database
You can use this command on a database that you plan to recover from tape backup
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16. DBCC CHECKTABLE Command
Checks for database corruption against a table.
You can use this command while people are using the table except while performing repair
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17. DBCC DBREINDEX Command
Command updates the indexes on a server
Indexes are used for faster data access
Indexes are stored like data pages and become fragmented over time
DBCC DBREINDEX command defragments indexes
Time required depends on:
Number of indexes
Size of indexes
Load on server when running command
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18. SQL 710 Physical structure of database Order 1 Item 1 Quantity Item 2
Insert Order 1 orderlines on Page 1:
Order 1
Item 1
Quantity
Item 2
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19. SQL 710 Physical structure of database (ctd) Order 1 Item 1 Client 1
Insert Order 2’s orderlines on Page 1(blue) and
page 2 (white)
Order 1
Item 1
Client 1
Item 2
Order 2
Client 2
Item 3
Item 4
Item 5
Item 6
Item 7
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20. SQL 710 Physical structure of database (ctd)
Add order 1 orderlines – no room on page 1 so place
on page 2 – data for order 1 is fragmented
Order 1
Item 1
Quantity
Item 2
Order 2
Item 3
Item 4
Item 5
Item 6
Item 7
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21. SQL 710 Physical structure of database (ctd)
Order 2 cancelled- delete Order 2’s orderlines –
leaves Order 1’s orderlines fragmented
Order 1
Item 1
Quantity
Item 2
Item 3
Item 4
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