OCA 06 - Managing Database Storage Structures

7/29/2019 OCA 06 - Managing Database Storage Structures

1/49

06 - Managing Database Storage

Structures

By Muhammad Asghar Khan

Reference: OCA Oracle Database 11g - Admin I Exam Guide by John Watson


2/49

Agenda

http://asghars.blogspot.com2

Understand Tablespaces and Datafiles

Tablespaces Segment Oracle Block Extents Data Files OS Block Exersice 6-1: Segments, Extents, Blocks

Oracle-Managed Files (OMF)

Automatic Storage Management (ASM) Local File System Clustered File System

1/3


3/49

Agenda


Raw Devices

ASM Devices

EXERCISE 6-2 Document a Databases Physical Structure

Create and Manage Tablespaces

Types of tablespaces

Tablespace extent management Tablespace segment management

Create Tablespace

Taking a Tablespace Online or Offline

Rename a Tablespace and Its Datafiles

Mark a Tablespace as Read Only

Resizing a Tablespace

Changing Alert Thresholds

Dropping Tablespaces

2/3


4/49

Agenda


EXERCISE 6-3: Create, Alter, and Drop Tablespaces Manage Space in Tablespaces

Extent Management

Segment Management

Manual Management

EXERCISE 6-4: Change Tablespace Characteristics

3/3


5/49



Data is stored logically in

segments and physically in

datafiles

The separation of logical

from physical storage is anecessary part of the

relational database

paradigm

Figure shows the Oracle

storage model sketched as

ERD

1/6


6/49



Tablespaces There is a many-to-many relationship b/w segment &

datafile

The tablespace resolves the many-to-many

relationship b/w segments and datafiles One tablespace can contain many segments and be

made up of many datafiles

This means that any one segment may be spread

across multiple datafiles, and any one datafile maycontain all of or parts of many segments

Tablespaces are identified by name, unique in thedatabase

2/6


7/49



Segment Represents any database object that stores data and

therefore requires space in a tablespace

Typical segment is a table, but there are other

segment types, notably index segments and undosegments

Any one segment can exist in only one tablespace,but the tablespace can spread it across all the files

making up the tablespace Segments are schema objects, identified by the

segment name qualified with the owning schemaname

3/6


8/49



Oracle Block Datafiles are formatted into Oracle blocks,

consecutively numbered

The size of the Oracle blocks is fixed for a tablespace;

the default (with release 11g) is 8 KB The size of an Oracle block can range from 2 KB to 16

KB on Linux or Windows, to 32 KB on some otheroperating systems

It is the unit of I/O for the database The block size is controlled by the parameter

DB_BLOCK_SIZE

4/6


9/49



Extents An extent is a set of consecutively numbered Oracle

blocks within one datafile

Managing space one block at a time would be a

crippling task, so blocks are grouped into extents

Every segment will consist of one or more extents,

consecutively numbered

Data File Datafile is, physically, made up of a number of

operating system blocks

5/6


10/49



Datafiles and the operating system blocks are entirely

dependent on the operating systems file system The alternatives to file systems for datafile storage are raw

devices or ASM

Raw devices are now very rarely used for datafile storagebecause of manageability issues

OS Block An operating system block is the unit of I/O for your file system

The operating system block size is configurable for some filesystems (for example, when formatting an NTFS file system youcan choose from 512 B to 64 KB), but typically system

administrators leave it on default (512 B for NTFS, 1 KB forext3)

The configuration that should always be avoided would bewhere the operating system blocks were bigger than theOracle blocks

6/6


11/49

Exersice 6-1: Segments, Extents, Blocks


1. Identify the segment types

2. Identify precisely where a segment is

i. First creates the table HR.NEWTAB

1/3


12/49



ii. Query DBA_EXTENTS to find the segment and

extent

Two extent is in file number 4 and each is 8 blocks

longiii. Force Oracle to allocate another extent to the

segment

2/3


13/49



iv. Query shows that this new extent

v. Determine the name of the file in which the extents

were allocated, and the name of the tablespace to

which the datafile belongs

3/3


14/49

Oracle-Managed Files (OMF)


Use of OMF is intended to remove the necessity for theDBA to have any knowledge of the file systems

To enable OMF, set some or all of these instanceparameters:

DB_CREATE_FILE_DEST DB_CREATE_ONLINE_LOG_DEST_1

DB_CREATE_ONLINE_LOG_DEST_2



DB_CREATE_ONLINE_LOG_DEST_5 DB_RECOVERY_FILE_DEST

OMF will generate filenames and (by default) set thefile sizes

1/1


15/49

Automatic Storage Management (ASM)


Datafiles can exist on four types of device: local filesystems, clustered file systems, ASM disk groups,

and raw devices

Local File System

Files exist as normal operating system files in a

directory structure on disks directly attached to the

computer running the instance

These could be internal IDE or SATA drives or moresophisticated SCSI disks, or external drives

1/6


16/49



Clustered File System

A clustered file system is external disks, mountedconcurrently on more than one computer

Clustered file systems can be bought from operatingsystem vendors, or Oracle Corporations OCFS (Oracle

Clustered File System) is an excellent alternative

Raw Devices

It is possible to create datafiles on disks with no filesystem at all

In old days before clustered file systems or ASM), rawdevices were the only way to implement a Parallel Serverdatabase

Parallel Server itself was replaced with RAC in database

release 9i

2/6


17/49



ASM Devices

ASM is a facility introduced with database release 10 g

ASM is a logical volume manager designed for Oracledatabase files

It cannot be used for the Oracle Home, or for the alert logand trace files

To set up ASM, the system administrators must providethe physical volumes. These can be actual disks, partitionsof disks, or devices provided by a SAN (storage area

network) or some form of network-attached storage(NAS)

ASM is covered in detail in the second OCP examination

3/6


18/49



The DBA then groups these physical volumes (known as

ASM disks) into logical volumes (known as ASM disk

groups)

The disk groups are formatted into allocation units,

which are contiguous blocks of space on a physical

volume

The default allocation unit size is 1 MB, but this can be

increased up to 64 MB if the nature of the application is

such (typically, a data warehouse) that it would benefit

from this

Every file created on an ASM disk group will always be

striped across all the ASM disks that make up the group

4/6


19/49



Mirroring is also enabled by default

If a volume group consists of just two disks and athird is added, ASM will automatically launch arebalance operation to bring it into use by restripingthe ASM files

Similarly, if a disk leaves the group, the disk group willimmediately rebalance itself to reinstantiate lostmirrors

A key feature of ASM is that it can work as a clustered

file system Figure on next slide sketches the ASM structures as

an entity-relationship diagram

5/6


20/49



6/6


21/49

EXERCISE 6-2 Document a Databases Physical

Structure


1. Determine the name and size of the controlfile(s)

2. Determine the name

and size of the online

redo log file members

1/2


22/49

EXERCISE 6-2 Document a Databases Physical

Structure


3. Determine the name andsize of the datafiles and the

tempfiles

2/2


23/49



All databases must have a SYSTEM tablespace and aSYSA UX tablespace, and (for practical purposes) atemporary tablespace and an undo tablespace

Subsequently, the DBA may create many moretablespaces for user data, and possible additionaltablespaces for undo and temporary data

Types of tablespaces

Permanent

A permanent tablespace stores regular schema objects, suchas tables and indexes

We can also enable the encryption for permanenttablespace

1/12


24/49



Temporary

Temporary tablespaces are used to store the temporarytables, temporary indexes and intermediate sort results

Undo

Undo tablespace stores only system-managed undo

segments Tablespace extent management

Dictionary Managed

Dictionary managed tablespaces are managed by the data

dictionary This is for backward compatibility; it is recommended that

you use locally managed tablespaces

2/12


25/49



Locally Managed

Locally managed tablespaces are managed via bitmaps

Extent allocation be automatic or uniform by

specifying the size

Tablespace segment management

Segement management for a tablespace can be

automatic or manual

Automatic segment management offers highperformance for free space managemen

3/12


26/49



Create Tablespace To create a tablespace with EM Database Control,

navigate Home PageServer Tab Storage Section

Tablespaces linkCreate Button

The Create Tablespace window prompts for a tablespacename, and the values for Extent Management, Type, and

Status

4/12


27/49



The Add button lets you specify one or more datafiles

for the new tablespace. Each file must have a name

and a size, and can optionally be set to autoextend up

to a maximum file size

5/12


28/49



The Storage tab gives access to options for extent

management and compression

6/12


29/49



Taking a Tablespace Online or Offline An online tablespace or datafile is available for use;

an offline tablespace or datafile exists as a definition

in the data dictionary and the controlfile but cannot

be used In EM on tablespaces page select newtab and clicke

Edit button

Select Offline from

Status section and

click Apply

7/12


30/49



Rename a Tablespace and Its Datafiles A tablespace can be renamed while it is in use, but to

rename a datafile, the datafiles must be offline

In edit mode on General tab you can change the

name for tablespace and click Apply

To rename datafile

8/12


31/49



Mark a Tablespace as Read Only

Making a tablespace read only, none of the objectswithin it can be changed with DML statements

Making a tablespace read only can have advantages

for backup and restore operations

Resizing a Tablespace A tablespace can be resized either by adding datafiles

to it or by adjusting the size of the existing datafiles

9/12


32/49



Changing Alert Thresholds

The MMON process of the instance monitors, how full everytablespace is

If a tablespace fills up beyond a certain point, MMON will raisean alert

The easiest way to see alerts, is to look at the database home

page of Database Control, where they are displayed in theAlerts section

To view or change the alert levels, select the tablespace andclick the Edit button, then in the Edit Tablespace window takethe Thresholds tab

The alert system uses the maximum possible size of thetablespace as the basis for its calculations, which ismeaningless if the tablespaces datafiles were created with thesyntax AUTOEXTEND ON MAXSIZE UMLIMITED, or if a MAXSIZEwas not specified

10/12


33/49



When using automatic extension, it is goo d practice

to set a maximum limit

11/12


34/49



Dropping Tablespaces To drop a tablespace, use the DROP TABLESPACE

command

12/12


35/49

EXERCISE 6-3: Create, Alter, and Drop Tablespaces


1.

Create a tablespace

2. Create a table in the new tablespace, anddetermine the size of the first extent

1/6


36/49



3.

Add extents manually, and observe the size ofeach new extent

2/6


37/49



4. Take the tablespace offline, observe the effect,

and bring it back online

3/6


38/49



5. Make the tablespace read only, observe the effect,

and make it read-write again

4/6


39/49



6. Enable OMF for datafile creation and create a

tablespace, using the minimum syntax now

possible

7. Determine the characteristics of the OMF file

5/6


40/49



8. Adjust the OMF file to have more sensible

characteristics

9. Drop the tablespace, and use an operating system

command to confirm that the file has indeed gone

6/6


41/49

Manage Space in Tablespaces


Space management in tablespace occuers at thefollowing levels

Tablespace, done by sizing data files (already discussed)

Segment, done by allocating extents

Row, done by maintaing bitmaps

Extent Management

There are two techniques for managing extent usage:dictionary management or local management

Dictionary Management It uses two tables in the data dictionary

SYS.UET$ has rows describing used extents, and SYS.FET$has rows describing free extents

Dictionary management should never be used

1/5


42/49



Local Management

It uses bitmaps stored in each datafile

Each bit in the bitmap covers a range of blocks, and

when space is allocated, the appropriate bits are

changed from zero to one When creating a locally managed tablespace, an

important option is uniform size

If you know how big segments are likely to be,

UNIFORM SIZE may well be the best option, otherwise

Oracle Corporation recommends AUTOALLOCATE

2/5


43/49



If a database has been upgraded from previous

versions, it will include dictionary-managed tablespaces

Any dictionary-managed tablespaces should beconverted to local management with this PL/SQL

procedure call

Segment Management

There are two techniques for managing segment

space usage: manual or automatic Automatic Management

Automatic Management should always be used

3/5


44/49



In an automatic management every segment created in

a tablespace has a set of bitmaps that describe how full

each block is

There are five bitmaps for each segment, and each

block will appear on exactly one bitmap

The bitmaps track the space used in bands:

Blocks that are 75% to 100% used

Blocks that are 50% to to 75% used



If the block size is 4 KB and the row to be inserted is

1500 bytes, an appropriate block will be found by

searching the 25% to 50% bitmap

4/5


45/49



As rows are inserted, are deleted, or change size

through updates, the bitmaps get updated accordingly

Manual Management

The old manual space management method used a free

list, which stated which blocks were available for insertbut without any information on how full they were

To see if any tablespaces are using manual

management

It is not possible to convert tablespace from manual to

automatic segment space management

5/5


46/49



1. Create a tablespace using manual segment space

management

2. Confirm that the new tablespace is indeed using

the manual technique

1/4

2/4


47/49



3. Create a table and an index in the tablespace.

These segments will be created with freelists, not

bitmaps

4. Create a new tablespace that will (by default) use

automatic segment space management

2/4

3/4


48/49



5. Move the objects into the new tablespace:

6. Confirm that the objects are in the correcttablespace

3/4

4/4


49/49


7. Drop the original tablespace

8. Rename the new tablespace to the original name.

This is often necessary, because some application

software checks tablespaces names

9. Tidy up by dropping the tablespace, first with this

command

4/4

Date post:	04-Apr-2018
Category:	Documents
Upload:	muhammad-asghar-khan
View:	220 times
Download:	0 times

OCA 06 - Managing Database Storage Structures

Documents