Locally Managed Tablespaces in Oracle8i Raghav Vinjamuri

2 Questions Extents – –Size of Individual Extent in a Segment Matters/Does Not Matter? – –Number of Extents Matters/Does Not Matter?

3 Questions ( AND Answers) Extents – –Size of Individual Extent in a Segment Matters /Does Not Matter? – –if small, can lead to numerous extents. – –Number of Extents Matters /does not matter? – –Due to overheads of dictionary maintenance, May not be for full table scan performance.

4 Questions ( AND Answers) Extent Management – –Extents must therefore be Fixed Size - Appropriately Large, Fixed in Number How to implement/manage Fixed Size Extents in an Oracle database?

5 Overview Extent Management – –Dictionary Managed Tablespaces - “DMT” – –Locally Managed Tablespaces - “LMT” Features/“Bugs”/“Usage Quirks” of LMTs in Oracle8 i Rel Benefits of LMTs over DMTs Summary & References Q&A

6 Extent Management How to implement Fixed Size Extents in an Oracle database? – –Pre-Oracle8 – –Oracle8 – –Oracle8 i

7 Extent Management Pre-Oracle8 – –DEFAULT STORAGE INITIAL and NEXT are set equal, and PCTINCREASE=0 Caveats – –Extent Sizes Rounded Up. Nearest Multiple of 5. MAYBE more (up to 4 additional blocks) if there are fewer than 5 blocks remaining in the unallocated portion. – –Coalescing of Free Extents by SMON. – –Extent Trimming After Parallel Operations.

8 Extent Management Oracle8 – –DEFAULT STORAGE INITIAL and NEXT are set equal, and PCTINCREASE=0 – –MINIMUM EXTENT integer the minimum size of an extent in a tablespace. controls free space fragmentation in tablespaces – –ensures every used/free extent size in a tablespace is at least as large as, and is a multiple of integer – –eliminates unwarranted extent size rounding/trimming

9 Extent Management D ictionary M anaged T ablespaces “DMT” – –Free/Used Extent information of tablespaces tracked via Data Dictionary Tables (FET$ and UET$) differentiates from L ocally M anaged T ablespaces in Oracle8 i

10 Locally Managed Tablespaces New in Oracle8 i EXTENT MANAGEMENT LOCAL clause of CREATE TABLESPACE statement – –EXTENT MANAGEMENT DICTIONARY still is Default. Allows Fixed Extent Size(s) – –AUTOALLOCATE or “System Determined” Sizes – –UNIFORM Size

11 Locally Managed Tablespaces Create Tablespace TESTLMT datafile ‘lmt01.dbf’ size 1000M reuse EXTENT MANAGEMENT LOCAL AUTOALLOCATE; Create Tablespace TESTLMT datafile ‘lmt01.dbf’ size 1000M reuse EXTENT MANAGEMENT LOCAL UNIFORM Size 10M;

12 Locally Managed Tablespaces AUTOALLOCATE – –is default – –can specify initial extent and Oracle determines the size of the rest, with a minimum of 64k UNIFORM – –default is 1MB

13 Locally Managed Tablespaces Summary Notes for DBA’s 1. LMTs and DMTs can co-exist in same DB. 2. EXTENT MANAGEMENT DICTIONARY is default. 3. Currently, a locally managed SYSTEM tablespace ( ?? For ROLLBACK SEGMENT usage ) cannot be created ( True in ) 4. EXTENT MANAGEMENT LOCAL CREATE TABLESPACE statement - for permanent tablespaces   CREATE TEMPORARY TABLESPACE statement - for temporary tablespaces

14 Locally Managed Tablespaces Summary Notes for DBA’s … 2   CREATE TEMPORARY TABLESPACE statement - for temporary tablespaces CREATE TEMPORARY TABLESPACE TEMP TEMPFILE 'temp.dbf' SIZE 256M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K; 5. When creating an LMT, AUTOALLOCATE is default. 6. Temporary LMT’s can only use UNIFORM SIZE, and not AUTOALLOCATE.

15 Locally Managed Tablespaces Summary Notes for DBA’s … 3 7. Parameters   TEMPORARY,   MINIMUM EXTENT, or   DEFAULT storage_clause,   NEXT,   PCTINCREASE,   MINEXTENTS,   MAXEXTENTS are not valid for locally managed tablespaces. Could get an error or be silently ignored!!

16 Locally Managed Tablespaces Summary Notes for DBA’s … 4 8. DBMS_SPACE_ADMIN package provides Defect Diagnosis and Repair Functionality for LMT Migration of DMT to LMT or vice-versa 9. LMTs can be altered for many of the same reasons as a dictionary-managed tablespace. However, altering storage parameters is not an option and coalescing free extents is unnecessary an LMT cannot be altered to a locally managed temporary tablespace.

17 Locally Managed Tablespaces Summary Notes for DBA’s … To find out which tablespaces are LMTs SELECTtablespace_name, extent_management FROM dba_tablespaces WHERE extent_management = 'LOCAL';

18 These slides (and, a white paper!) will be posted on the NOCOUG web site, at

19 Questions ?

20 Good Luck!