PERMANENT TABLESPACE MANAGEMENT:

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1 PERMANENT TABLESPACE MANAGEMENT: A Tablespace is a logical storage which contains one or more datafiles. A database has mul8ple tablespaces to Separate user data from data dic8onary data to reduce I/O conten8on. Separate data of one applica8on from the data of another to prevent mul8ple applica8ons from being affected if a tablespace must be taken offline. Store different the datafiles of different tablespaces on different disk drives to reduce I/O conten8on. Take individual tablespaces offline while others remain online, providing beder overall availability. Op8mizing tablespace use by reserving a tablespace for a par8cular type of database use, such as high update ac8vity, read-only ac8vity, or temporary segment storage. Back up individual tablespaces. By default a tablespace will be a small file tablespace in which the maximum datafile size can be 32G(2^22-1*8KB). A BIGFILE tablespace will only have 1 datafile with maximum size of 32TB(s^22-1*8KB) which reduce the total number of files in the database there by reduce the control file size. DICTIONARY Managed Tablespace will store the extent alloca8on informa8on in the system tablespace in UET and FET tables whever space is required to these tablespaces ST enqueue must be aquired by a process which leads to conten8on. Locally Managed Tablespace: Locally managed tablespaces track all extent informa8on in the tablespace itself by using bitmaps, resul8ng in the following benefits: ast, concurrent space opera8ons. Space alloca8ons and dealloca8ons modify locally managed resources (bitmaps stored in header files). Enhanced performance Readable standby databases are allowed, because locally managed temporary tablespaces do not generate any undo or redo. Space alloca8on is simplified, because when the AUTOALLOCATE clause is specified, the database automa8cally selects the appropriate extent size. User reliance on the data dic8onary is reduced, because the necessary informa8on is stored in file headers and bitmap blocks. Coalescing free extents is unnecessary for locally managed tablespaces. A system tablespace can be locally managed and if it is locally managed then all the tablespaces in the database will be locally managed tablespace.

2 EXTENT ALLOCATION: AUTOALLOCATE specifies that extent sizes are system managed. Oracle will choose "op8mal" next extent sizes star8ng with 64KB. As the segment grows larger extent sizes will increase to 1MB, 8MB, and eventually to 64MB. This is the recommended op8on for a low or unmanaged environment. UNIFORM specifies that the tablespace is managed with uniform extents of SIZE bytes (use K or M to specify the extent size in kilobytes or megabytes). The default size is 1M. The uniform extent size of a locally managed tablespace cannot be overridden when a schema object, such as a table or an index, is created. SEGMENT SPACE MANAGEMENT: AUTO: In Automa8c segment space managed bitmap is used to manage free blocks of a segment contrast to manual segment space management it is self tuning and we can just specifiy INITRANS,PCT FREE. MANUAL: where we specify all the segment space configura8on proper8es PCT USED,PCT FREE,INITRANS,FREELISTS Crea8ng Tablespace: Below is the syntax to create a tablespace. Create [BIGFILE] tablespace <Tablespace-name> Datafile '<dfile locanon>' <size>,.. [datafile-n <dfile-locanon>] extent management < local/dicnonary> [uniform <extent-size>/auto] segment space <Auto/manual> [auto extend on next <size> maxsize <max-size>] [Blocksize <size>];àto create non standard block size tablespace. Dba_data_files/v$datafile will provide the informa8on about datafiles present in the tablespace. Dba_free_Space will provide the space available in the tablespace. Dba_Tablespaces will provide informa8on about tablespaces.

3 To manage space in the tablespace: To add space to tablespace we use 1. If datafile size is not the maxsize then we alter the file-size as SQL>alter database datafile '<datafile-loca8on> resize <new-size>; 2. If the datafile size reached maxsize then we add another datafile to the tablespace. SQL>alter tablespace <TS-NAME> add datafile '<datafile-loca8on> size <size>; To shrink the tablespace: We can shrink the tablespace provided the datafile HWM is below the size to be shrinked. SQL>alter database datafile '<datafile-loca8on' resize <shrinked_size>; We cannot drop a datafile from a tablespace prior to 10g and in later version we can drop it if it is an empty and not first datafile in the tablespace. SQL>alter tablespace <TS-NAME> drop datafile '<datafile-loca8on>';-àto dro a datafile which is empty. To make the tablespace read-only, we cannot put a datafile in read only. SQL>alter tablespace <TS-NAME> read only; and read write to make it writable again. To make tablespace or datafile offline-ànot availabe for i/o opera8ons. SQL>alter tablespace <TS-NAME> offline; SQL>alter datatabase '<datafile-loca8on>' offline; and online to bring it back to online again. To Drop a tablespace: SQL>DROP TABLESPACE <TS-NAME> [<including contents and datafiles>]; To rename a tablespace: SQL>ALTER TABLESPACE <TS-NAME> rename to <new-ts-name>;

4 To rename a datafile: SQL>alter database datafile '<datafile-loca8on>' offline. $]copy the file to new-name SQL>alter database rename file '<datafile-loca8on' to <new-datafile name with loca8on'>; SQL>recover datafile <datafile-loca8on>; SQL>alter database '<new-datafile-name> online; To find the HWM of a datafile: SQL>select (max((block_id+blocks-1)*8192))/1024/1024 "HWM (MB)" from dba_extents where file_id=5; If the space is fragmented in the datafile and you need to shrink it. We have to take the export of objects from the database. Create a new tablespace and import it to database. Datafile S1 S2 S3 dropped S4 S5 S6 HWM S7 S8 dropped S9 last segment

5 TEMPORARY TABLESPACE MANAGEMENT: A Temporary tablespace contains transient data that persists only for the dura8on of the session. Temporary tablespaces can improve the concurrency of mul8ple sort opera8ons, reduce their overhead, and avoid Oracle Database space management opera8ons. A temporary tablespace can be assigned to users with the CREATE USER or ALTER USER statement and can be shared by mul8ple users. A temporary tablespace will have one or more tempfiles. Informa8on about tempfiles is present in dba_temp_files. To create temporary tablespace: SQL>Create temporary tablespace <Tablespa tempfile '<dfile locanon>' <size>,.. [datafile-n <dfile-locanon>] extent management < local/dicnonary> uniform <extent-size> [auto extend on next <size> maxsize <max-size>]; Auto allocate is not allowed in temporary tablespace. We cannot explicitly create objects in temporary tablespace. To verify the temp tablespace usagewe use below query: SQL>--query to check the temporary tablespaces uasge by the users SELECT b.tablespace, ROUND(((b.blocks*p.value)/1024/1024/1024),2) 'G' "SIZE,a.sid ',' a.serial# SID_SERIAL, a.username,a.program FROM sys.v_$session a,sys.v_$sort_usage b,sys.v_$parameter p WHERE p.name = 'db_block_size' AND a.saddr = b.session_addr ORDER BY b.tablespace, b.blocks;

6 Undo tablespace management: Undo tablespace is used to Roll back transac8ons when a ROLLBACK statement is issued Recover the database Provide read consistency Analyze data as of an earlier point in 8me by using Oracle Flashback Query Recover from logical corrup8ons using Oracle Flashback features Undo_retension: undo retension specifies the mimimum 8me un8l which undo segments to be retained in undo tablespace. This parameter is autotuned by oracle to more than the length of long running statement provided autoextend is turned on for the undo tablespace. For fixed undo tablespace oracle dynamically tunes the reten8on period. Each block in undo tablespace can be ac8ve,unxpired and expired. Ac8ve:Blocks related the ongoing transac8on and required for rollback. Oracle Will never overwrite the undo blocks. Expired:blocks related to commited transac8on and undo_reten8on has passed. Blocks no longer required for read consistency and the first choice to overwrite the blocks for new transac8ons if there is no available space in undo. Unexpired:Blocks related to commided transac8on but undo_reten8ons has not passed yet. You s8ll need this for read consistency but if there are no expired blocks and there is no free space then oracle overwrite unexpired blocks and that causes ORA snapshot too old error for the session which are reading from undo tablespace. To avoid ORA error either we need to reduce frequent commits or we need to create undo tablespace with ren8on guarantee which will guarantee that unexpired blocks will never be overwriden. We can create more than 1 undo tablespace but only 1 undo tablespace can be ac8ve for an instance. Undo_tablespace parameter specifies the ac8ve undo tablespace.

7 Below is the syntax to create undo tablespace: SQL>CREATE UNDO TABLESPACE <tablespace-name> DATAFILE '<datafile-loca8on' SIZE <size> AUTOEXTEND ON; Below command provides the undo usage. Select s.sid,s.serial#, s.schemaname,s.program,t.status,t.start_date, (t.used_ublk*8192/1024/1024) Mbytes from v$transac8on t,v$session s where s.taddr=t.addr; Dba_undo_extents will provide the info about the undo blocks status. select status, round(sum_bytes / (1024*1024), 0) as MB, round((sum_bytes / undo_size) * 100, 0) as PERC from ( select status, sum(bytes) sum_bytes from dba_undo_extents group by status ), ( select sum(a.bytes) undo_size from dba_tablespaces c join v$tablespace b on b.name = c.tablespace_name join v$datafile a on a.ts# = b.ts# where c.contents = 'UNDO' and c.status = 'ONLINE' );