IT Database Administration Section 03

Tablespaces and the DBA  Important for DBAs – logical units of database storage Made up of physical operating-system files (one or more) Made up of physical operating-system files (one or more)  Can be made READ ONLY (data warehouse) READ ONLY (data warehouse) PERMANENT or TEMPORARY (holds sort data) PERMANENT or TEMPORARY (holds sort data)  Can be put Online or Offline

Tablespaces: The Issues  Schemes for space allocation for users and applications Give users resource quotas on tablespaces Give users resource quotas on tablespaces Provide separate default storage parameters for each tablespace Provide separate default storage parameters for each tablespace  Design tablespaces for different styles of activity  Group tables belonging to one application  Put tables of high activity on certain physical devices

Tablespaces: The Issues  Positioning index and table data – spread the I/O Spread large active tables across disks (table striping) Spread large active tables across disks (table striping)  Tablespaces for rollback segments Have separately designed tablespaces for rollback segments Have separately designed tablespaces for rollback segments  Tablespaces for TEMPORARY segments  Used to temporarily store sort runs for many types of queries

Points to Consider  Tablespaces are transferable across databases with version 8i and up  May go offline when certain errors occur  Access to data is restricted if an index is in an offline tablespace  Recovery can be performed tablespace by tablespace

The SYSTEM tablespace – at least 60mb  Every database must have a tablespace called SYSTEM Automatically built by CREATE DATABASE with default storage characteristics as specified in the file sql.bsq Automatically built by CREATE DATABASE with default storage characteristics as specified in the file sql.bsq  The SYSTEM tablespace contains  The Data Dictionary  SYSTEM rollback segments  Bootstrap segment

The SYSTEM tablespace – cont’d  May be enlarged – with careful forethought Do not store any user data in SYSTEM Do not store any user data in SYSTEM Reserved only for Oracle Reserved only for Oracle  Must always be online for normal operations  Can be set to be locally managed with the  Extent Management Local statement in the Create Database clause

Creating Additional Tablespaces  The creator must have DBA role or be granted the CREATE TABLESPACE system privilege  Example CREATE TABLESPACE statement Create Tablespace user_data_01 Create Tablespace user_data_01 Datafile ‘e:\oraclass\database\user_data_01.dbf’ size 200M Datafile ‘e:\oraclass\database\user_data_01.dbf’ size 200M Autoextend on next maxsize unlimited Autoextend on next maxsize unlimited Default storage (Initial 1M Default storage (Initial 1M Next 2M Next 2M Pctincrease 0 Pctincrease 0 Maxextents 100) Maxextents 100) Permanent; Permanent;

The SYSTEM tablespace – Example cont’d  Uses a 200 MB file as storage for the tablespace This will automatically expand as it becomes full This will automatically expand as it becomes full  Objects without their own storage definition will be allocated an initial 1MB of space, and all other extents will be 2MB  Objects can expand to a maximum of 100 extents

Creating the first additional tablespace(s)  Non-SYSTEM tablespace data cannot make use of the system rollback segment, so…  Create the tablespace(s)  Create rollback segments as required (at least one) in the new tablespace(s)  Bring the rollback segments online so that transactions on non-SYSTEM tablespace data can use a rollback segment  This is not online by default  Edit the parameter file to include names of the new rollback segments in order to make them active when opening the database

Altering Tablespaces  Why alter tablespaces?  Add a file to satisfy additional space requirements  Rename files because they need to be moved to other devices  Make the tablespace available or unavailable to users  Perform an online backup of the tablespace  Change the way in which files behave when, and if, they expand  Change the maximum size of any auto-expandable files  Change to read-only or read/write  Force coalescence of free space  Change the default storage parameters  Change a tablespace from temporary to permanent  Change the extent management  Particularly important for temporary tablespaces

Altering Tablespaces: Adding Datafiles  Enlarging tablespaces (adding datafiles) Alter Tablespace tablespacename Alter Tablespace tablespacename Add Datafile ‘filename.dbf’ [Size interger [k|m] ] Add Datafile ‘filename.dbf’ [Size interger [k|m] ]  Tablespace may be online or offline, but the database must be open The extra file is automatically enabled and available The extra file is automatically enabled and available Default file size is 10MB Default file size is 10MB  If SIZE is specified the file must not exist and is created with the specified size

Altering Tablespaces: Relocating Files  Renaming files in a tablespace Alter Tablespace tablespacename Alter Tablespace tablespacename Rename Datafile ‘/usr1/data2.dbf’ To ‘/usr2/data3.dbf’; Rename Datafile ‘/usr1/data2.dbf’ To ‘/usr2/data3.dbf’;  Renaming (relocating) a datafile actually requires a number of operations  Take the tablespace offline  Use the OS to copy the old file to the new location  Use the RENAME DATAFILE statement  Make the tablespace ONLINE  Delete the old file using the OS  Backup the database and control files  This method requires the database to be OPEN

Altering Tablespaces: Relocating Files cont’d  Files can also be renamed when the database is in a MOUNT state and OPEN Alter Database Rename File ’/usr1/system_data2.dbs’ Alter Database Rename File ’/usr1/system_data2.dbs’ To ‘/usr2/system_data3.dbf’; To ‘/usr2/system_data3.dbf’;  This statement does not physically move the files

Altering Tablespaces: Changing the Default Storage Alter Tablespace usr1 Default Storage ( Initial 1M Next 2M Next 2M Minextents 1 Minextents 1 Maxextents 100 Maxextents 100 Pctincrease 50); Pctincrease 50); The new values have no retro-effect The new values have no retro-effect  They do not change any existing storage allocation

Altering Tablespaces: Online and Offline  Bring tablespaces online Alter Tablespace tablespacename Online; Alter Tablespace tablespacename Online;  Tablespace becomes available for use  Will be successful if there are no errors in the datafiles in the tablespace

Altering Tablespaces: Online and Offline  Bring tablespaces offline Alter Tablespace tablespacename Offline Alter Tablespace tablespacename Offline [ Normal | Immediate | Temporary | For Recover ]; [ Normal | Immediate | Temporary | For Recover ];  Taking a tablespace offline enables the following actions:  Make the data temporarily unavailable to users  Change disks  Handle disk failures

Altering Tablespaces: Offline Options  NORMAL No media recovery necessary No media recovery necessary The datafiles in the tablespace are checkpointed The datafiles in the tablespace are checkpointed NOARCHIVELOG mode NOARCHIVELOG mode  IMMEDIATE  Not available in NOARCHIVELOG mode because the tablespace will require media recovery before subsequent use  No checkpoint is performed and files do not need to exist  ARCIVELOG mode only

Altering Tablespaces: Offline Options cont’d  TEMPORARY Can be done if one of the datafiles is already offline Can be done if one of the datafiles is already offline All remaining datafiles within the tablespace are checkpointed All remaining datafiles within the tablespace are checkpointed Media recovery will be required for any of the files that are offline Media recovery will be required for any of the files that are offline ARCIVELOG mode only ARCIVELOG mode only  FOR RECOVER  Takes tablespaces offline for point in time tablespace recovery  ARCIVELOG mode only

Dropping Tablespaces Drop Tablespace tablespacename;  If data is present, the INCLUDING CONTENTS clause must be used Drop Tablespace tablespacename Including Contents;

Dropping Tablespaces cont’d  If foreign key constraints are acting on the data from tables in other tablespaces, use the CASCADE CONTENTS clause Drop Tablespace tablespacename Including Contents Cascade Contents;

Dropping Tablespaces cont’d  The DROP TABLESPACE command is a DDL statement; hence, no rollback is possible!  A Permanent Action  Recommended to take the tablespace offline before dropping it, and backup the database before and after the drop  Cannot be dropped if active rollback segments are present

Read-Only Tablespaces Alter Tablespace tablespacename Read Only; Alter Tablespace tablespacename Read Only;  Useful for  Static Data  Data Warehouse  Preventing Updates  Simplifying the backup strategy

Read-Only Tablespaces  Prerequisites  Tablespace must be online  No active transactions in the tablespace  No active rollback segments in the tablespace  No online backup currently running

Making a Tablespace Read-Only  Make sure the prerequisites are met  Set the tablespace to be read-only  Backup the tablespace  Amend the backup strategy and scripts  If could also be useful to scan all blocks in the tablespace to force block clean-out before making the tablespace read-only  To return a tablespace to read/write status Alter Tablespace tablespacename Read Write; Alter Tablespace tablespacename Read Write;

Temporary Tablespaces  Scratch areas used by Oracle  Tablespaces specially designed to hold data from intermediate sort runs  Large sorts may require too much space to be managed within memory  The creation of an index could require a temporary segment twice as large as the storage allocated for the actual index  The temporary sort data will be placed transiently on disk then  Beware: The default tablespace for temporary data is SYSTEM  The SYSTEM tablespace could become fragmented due to extents being continually allocated and deallocated to the sort runs  Each user should have a specified temporary tablespace for their sort data

Temporary Tablespaces cont’d  The temporary tablespace should have a default storage pattern so that each extent is exactly the same size (uniform extents)  Makes it easier for Oracle to find free space extents of the required size

Locally Managed Temporary Tablespaces  Preferred method Create Temporary Tablespace tablespacename Tempfile ‘tablespacename_fl.tmp’ Size 50M Extent Management Local Uniform Size 8M;  Extent management must be local when using this syntax  This tablespace cannot be renamed or made read-only  Media recovery does not recognize tempfiles because  There is no need to back them up  They are easy to re-create anytime needed

Coalescing Free Space in Tablespaces  Free-space fragmentation needs to be avoided  Caused by allocation and deallocation of storage to objects leaving small pieces of free space  Each piece may not be large enough for any future allocation of contiguous storage  Free space coalescion can be forced by Alter Tablespace tablespacename Coalesce; Alter Tablespace tablespacename Coalesce;

Retrieving Information about Fragmentation Select tablespace_name As tablespace, Select tablespace_name As tablespace, file_id As File_No, Count(*) As Pieces, file_id As File_No, Count(*) As Pieces, Max(blocks) As Max, Min(blocks) As Min, Max(blocks) As Max, Min(blocks) As Min, Avg(block) As Ave, Sum(blocks) As Tot Avg(block) As Ave, Sum(blocks) As Tot From dba_free_space From dba_free_space Where tablespace_name = ‘&tablespace’ Where tablespace_name = ‘&tablespace’ Group By tablespace_name, file_id; Group By tablespace_name, file_id;  The higher the pieces amount the greater the fragmentation

Oracle Files  Datafiles - operating-system files that are used to  Store Oracle Data  Position the physical separation of objects  Indexes from data  Enable the “Table Striping” technique  Support Table Partitioning  Redo Log Files store (all) changes to database data and contain  Before Images  After Images  Commit and Rollback Status  Checkpoint Information

Oracle Files cont’d  Control files store startup and backup/recovery information  Parameter files store initialization parameters  Password files  Trace, log, and networking files  Datafiles  Datafiles per Tablespace 1023  Datafiles per Database65533  Datafile Size4M Blocks  DB-BLOCK_SIZE32KB  Tablespaces per Database64000

Resizable Datafiles  To manually increase or decrease the size of a datafile: Alter Database Datafile filename Resize 100M;  To initiate automatic extension of a datafile: Alter Database Datafile filename Autoextend On Next nM Maxsize 80M; (Where n = the default number of blocks in one Oracle block)

Resizable Datafiles cont’d  To curtail automatic extension: Alter Database Datafile filename Autoextend Off;  To allow unlimited expansion: Alter Database Datafile filename Autoextend On Maxsize Unlimited;

General Database Storage Patterns  Oracle supports the use of:  Devices Partitions  RAID systems  Striping Techniques  Operating-System Driven  Database Driven  Device Partitions can give a 5-20% performance improvement  RAID configurations supported: RAID 1 RAID 1 RAID 5 RAID 5 RAID 0+1 RAID 0+1  Striping techniques are best done by the OS

Control Files  Created at database creation time and checked each time Oracle is started and the database is opened  Relatively small binary files  Size depends partly on the number of redo log files, database files, and information associated with backup and recovery  Contain information about: Database Files Database Files Redo Log Files (Name and Position) Redo Log Files (Name and Position) Timestamps of Creations Timestamps of Creations Checkpoint Information Checkpoint Information Backup and Recovery Information Backup and Recovery Information  Can become quite large in size

Control Files cont’d  Place a control file on each disk to guard against media failure  Copies are automatically written in synchronous fashion by Oracle with negligible performance overhead

Redo Log Files  Contain: Before Images Before Images After Images After Images Commit Information Commit Information Rollback Information Rollback Information Checkpoint Information Checkpoint Information  Safeguard changes to the database  Log files can be archived to enable full recovery  Incurs storage and management overhead  Can provide for total recovery

Redo Log Files cont’d  Should be entirely dualed (mirrored) on separate disks Log files can be volatile Log files can be volatile  Used to store redo log entries in a sequential manner Minimum of two log files required Minimum of two log files required Used in a circular fashion Used in a circular fashion  Contain roll forward data and backup of rollback segment data  Minimum size is 50KB (Never make them this small)  Default size is 500KB  Typically 10 – 100 MB

Questions?