Quản trị cơ sở dữ liệu Oracle 09 oracle storage

• A datafile can be associated with only one tablespace and only one database • A datafile is physically made up of a number of operating system blocks... Segments, Extents, Blocks, and

Oracle storage

Tổng quan về tablespace và datafile

• Dữ liệu được lưu trữ luận lý trong segment (thông thường là table), và lưu trữ vật

lý trong datafile

• Một tablespace có thể chứa nhiều segment và được tạo thành từ nhiều datafile

Mô hình lưu trữ dữ liệu Oracle

Operating system block

• is the basic unit of I/O for file system

• is the minimum unit of data that the operating system can read or write

• A datafile can be associated with only one tablespace and only one database

• A datafile is physically made up of a number of operating system blocks.

Segments, Extents, Blocks, and Rows

• A segment is a set of extents that contains all the data for a specific logical storage structure within a tablespace

• Every segment is comprised of one or more extents

• An extent consists of a set of consecutively numbered blocks

• A data block is the smallest unit of data, Oracle Database stores data in data blocks

The relationships among segments, extents, and data blocks

Create and Manage Tablespaces

• Example: Using Tablespace

create tablespace tbs_user datafile ' userdata _01.dbf' size 10M

Create table T (a NUMBER)

tablespace tbs_user ;

Bigfile and smallfile tablespace

• bigfile tablespace:

– Constain a single large file

– can be 1024 times larger than a smallfile tablespace

• Smallfile tablespace (default):

– can contain up to 1024 files

- CREATE BIGFILE TABLESPACE user_tbs

DATAFILE ‘oradata/grid/user_tbs01.dbf’ SIZE 1024 M;

- ALTER TABLESPACE user_tbs RESIZE 10G;

Space Management in Tablespaces

• Extent Management

• Segment Space Management

Extent Management

• Locally managed tablespaces (default)

– uses bitmaps stored in each datafile

– Each bit in the bitmap covers a range of blocks

– Bit value indicates free or used (0-free, 1 used)

• Dictionary-managed tablespaces

– Free extents recorded in data dictionary tables (SYS.UET$ and FET$)

Extent Management

Locally Managed Tablespaces

• Every extent allocated in this tablespace will be 160MB, the bitmap needs only

64 bits

• Oracle will allocate extents of 64KB up to 16 extents, from which it will allocate progressively larger extents

create tablespace large_tabs datafile 'large_tabs_01.dbf' size 10g extent management local uniform size 160m;

create tablespace any_tabs datafile 'any_tabs_01.dbf' size 10g

extent management local autoallocate;

Segment Space Management

• is set per tablespace and applies to all segments in the tablespace

• There are two techniques: manual or automatic

• There are five bitmaps for each segment: for full blocks used, 75- 100 percent used; 50 - 75 percent used; 25 - 50 percent used; and 0 - 25 percent used

Segment Space Management

• For instance,

– if the block size is 4KB and the row to be inserted is 1500 bytes

– an appropriate block will be found by searching the 25 percent to 50 percent bitmap

– Every block on this bitmap is guaranteed to have at least 2KB of free space.

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

• cannot take the following tablespaces offline

– SYSTEM

– The undo tablespace

– Temporary tablespaces

Taking a Tablespace Online or Offline

• ALTER TABLESPACE tablespacename OFFLINE [NORMAL | IMMEDIATE |

TEMPORARY];

– ALTER TABLESPACE users OFFLINE

• To bring a tablespace online

– ALTER TABLESPACE users ONLINE;

Mark a Tablespace as Read Only

• makes the flights tablespace read-only:

– ALTER TABLESPACE flights READ ONLY;

• makes the flights tablespace writable:

– ALTER TABLESPACE flights READ WRITE;

Rename a Tablespace and Its Datafiles

Resize a Tablespace

• Add a data file

• Change the size of a data file

– Automatically

– Manually

Add datafile to a tablespace

• alter tablespace storedata add datafile ‘STOREDATA_03.DBF' size 50m;

Change size of datafile Manually

• alter database datafile '/oradata/users02.dbf' resize 10m;

enable automatic extension of datafile

• alter database datafile ‘ \STOREDATA_03.DBF‘ autoextend on next 50m maxsize 2g;

Dropping Tablespaces

• Tablespace removed from data dictionary

• Optionally, contents removed from data dictionary

• OS files can be deleted with the optional AND DATAFILES clause

– DROP TABLESPACE tbs_02 INCLUDING CONTENTS AND DATAFILES;

Obtain Tablespace Info