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QUESTIONS ON BACKUP AND RECOVERY

1. What is the value of cold backup?2. What's the difference between startup

and startup mount? When we do "alter database open“, what does it mean?

3. What's the archive log function?4. When I did 'alter database open', I still

get an error. But once I issued 'recover database' and then 'alter database open‘, everything works just fine. What happens between these steps?

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MODULE 4 DATABASE TUNINGSection 5 Optimization of Physical Design

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TECHNIQUES FOR OPTIMIZING DATABASE

Partitioning – breaking a single large table into sections (partitions) stored in multiple files

Raw versus file systems – OS-controlled file or not

Clustering – enforcing the physical sequence of data on disk

Free space and compression – storage management

File placement and allocation Page size (block size in Oracle) – using the

proper page size for efficient data storage and I/O

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PARTITIONING Partitioning supports very large tables and indexes by decomposing

them into smaller and more manageable pieces called partitions.

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SQL queries and DML statements do not need to be modified in order to access partitioned tables

After partitions are defined, DDL statement can access and manipulate individual partitions if they choose to, rather than entire tables or indexes

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RAW DEVICE VS. FILE SYSTEM

Raw device is a UNIX feature to bypass operating system cache mechanism.

File system is a common way to manage storage.

Raw device might provide a slight performance benefit, but the database storage management is a nightmare.

Unless it is required by DBMS features, you should avoid to implementing Raw Device.

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CLUSTERING

Clustering is used to store one or more tables physically together with the share common columns and are often used together.

Because related rows are physically stored together, disk access time improves.

Clustering usually is enforced by the DBMS with a cluster index.

Like indexes, clusters do not affect application design. Data stored in a clustered table is accessed by SQL in the same way as data stored in a non-clustered table.

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CLUSTERING EXAMPLE

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FREE SPACE AND COMPRESSION

Free space – pre-allocate storage of tablespace, tables and indexes to store newly added data In DDL statements, a parameter is PCTFREE Benefits and disadvantages are listed in the

textbook Compression – shrink the size of a

database Tables or indexes can be algorithmically

compressed. The DMBS will handle the reading and writing

automatically.

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FILE PLACEMENT AND ALLOCATION

A database is very I/O intensive, the location of the files can be critical to database performance and recovery.

Separate the indexes from the data – traditional approach Analyze the access patterns of your applications and

separate the files for tables/indexes that are frequently accessed together

Place transaction logs on a separate disk device from the actual data, and spread out log members (redo01.log, redo02.log, redo03.log) to different physical disk devices

Place control files (control01.ctl, control02.ctl, control03.ctl) like transaction logs to different physical disk devices. It’s common to have control01.ctl shares the same device with redo01.log, etc.

Place archive logs on a complete separate disk device from any database files

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BLOCK SIZE

The block or page size is the smallest unit of I/O, and used to store data records.

The size selection is depending on record lengths – small block size is good for small record length; large block size is good for long record length

Typical page size are 2K, 4K, 8K, 16K, and 32K.

Common used sizes are 2K and 4K Data Warehouse or Data Mart applications

use 8K, 16K or 32K. Oracle allows to specify block size on

tablespace level – tablespace for small row-size tables uses 2K, tablespace for large row-size tables uses 8K.

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MODULE 4 DATABASE TUNINGSection 6 Storage Management

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SPACE MANAGEMENT

As a DBA, you should track the following: Objects approaching an “out of space”

condition Free space available – physical and logical

perspective Segment or partition size – understand large

or small tables Number of extents – less than hundreds Fragment usage information – performance

concern Amount of reserved space that is currently

unused – any waste situation

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DATA PAGE LAYOUTS

Three basic components exist in a data page (block in Oracle term)

Page header – general page information, such as a page identifier, an identifier indicating to which table the page belongs, free space pointers

Offset table – pointers to each data row on the data page

Data rows – actual rows of user data (table or index) Row header – general row information, such as row length,

information on variable-length data Offset tables – pointers to manage and control for variable-

length fields Row data – actual data for the row

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RAID TECHNOLOGY (WEEK 6)

RAID is an acronym for Redundant Arrays of Inexpensive Disks. Please refer http://www.acnc.com/04_01_00.html

RAID-0 – data striping: striped disk array without fault tolerance.

RAID-1 – data mirroring: all data is written to two or more drives.

RAID-5 – data stripping with distributed parity blocks, and it requires a minimum of 3 drives to implement (commonly 5 drives)

RAID-10 – mirrored data stripping: very high reliability with high performance.

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MODERN STORAGE TECHNOLOGY Storage Area Networks (SAN) – interconnected

network of storage devices (dedicate connections between host and storage) Shared storage between multiple hosts High I/O performance Server and storage consolidation Used for database files, I/O intensive/high

performance Network-Attached Storage (NAS) – storage that can

be accessed directly from the network Shared storage between multiple hosts Simpler management due to reducing duplicate

storage Application based storage access at file level Good for shared folders, program files

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MODULE 4 DATABASE TUNINGSection 7 Data Movement and Distribution in Oracle

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THE LOAD UTILITY

Oracle has SQL*Loader utility to perform bulk inserts of data into database tables.

You can transform data before loading You can selectively load from the input file

based on conditions You can load all or part of a table You can perform simultaneous data loads Two main steps to use SQL*Loader

Prepare the data file – contains data in certain formats, field terminators

Create a control file – defines how to map the data fields to a table and specifies if the data needs to be transformed

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DATA PUMP EXPORT AND IMPORT

Oracle offers the Data Pump technology for fast data movement between Oracle databases.

Migrating databases from development to test or production

Copying data between dev/test and production databases

Transferring data between Oracle databases on different operating system platforms

Backing up important tables or databases Reorganizing fragmented table data Extracting the DDL for tables and other objects

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DATA PUMP EXPORT EXAMPLES

Create a directory in Operating System for the dump directory C:\app\Administrator\admin\orcl450\dpdir1

Within Oracle, define and verify the directory for Data PumpSQL> create directory dpdir1 as ‘C:\app\Administrator\admin\

orcl450\dpdir1’;SQL> select * from dba_directories where directory_name like 'DP%';

Export a table from command line (Run-> cmd)C:\> expdp system/password TABLES=hr.employees

DIRECTORY=dpdir1 dumpfile=output01.dmp

Export a schemaC:\> expdp system/password SCHEMAS=hr DIRECTORY=dpdir1

dumpfile=output02.dmp

You can also export a tablespace or full database

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DATA PUMP IMPORT EXAMPLES

You can import the information from the dump file generated from Export.

Import to extract the DDL from the export dump fileC:\> impdp system/password DIRECTORY=dpdir1

dumpfile=output01.dmp SQLFILE=emp01.sql

Import a table to another schemaC:\> impdp system/password DIRECTORY=dpdir1

dumpfile=output01.dmp REMAP_SCHEMA=hr:scott

You can also import a schema, tablespace or full database

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DATABASE REFRESHING OPTIONS

Backup and restore Backup the source database, and restore to the target

location Commonly used for full database refresh Bath databases have similar physical structures

Data pump Export the source database/schema/table, and then

import to the target database Can be used for full, schema, or table level database

refresh

SQL*Loader Dump the source database tables to files in certain

format, and then use SQL*Loader to upload the table data Often used for table refresh, different DMBS, or user ad-

hoc files

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LOCK CONFLICTS A share lock partially locks data where there

is still partial access allowed to data by other sessions

An exclusive lock completely prohibits changes to data, but still allows read access

Locking of transactions and tables (using transactional control commands or LOCK TABLE) create locking situations manually

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0HOW TO DETECT LOCK

CONFLICTS

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0HOW TO DETECT LOCK

CONFLICTS

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HOW TO DETECT LOCK CONFLICTS

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WHAT IS A DEADLOCK? Deadlock: one thing is waiting for another,

but that other thing is also waiting for something A pending lock request cannot be serviced,

because the lock required will never be released Can cause serious performance issues

Most common cause is manual locking of data using LOCK TABLE or the FOR UPDATE clause

Usually deadlocked sessions must be rolled back manually Ways of resolving a deadlock manually are:

Rollback one of the deadlocked transactions Kill one of the sessions executing one of the

deadlocked transactions

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