EXTENTS discussion proposal

Proposal for Group discussion Some One-Liners about EXTENTS... 1. An EXTENT is a physical unit of storage. 2. EXTENTS are defined in Kilobytes. 3. A TABLE has a FIRST EXTENT and a NEXT EXTENT size. 4. EXTENTS are contiguous PAGES contained in a CHUNK. 5. Define the FIRST SIZE and NEXT SIZE of EXTENTS when creating the TABLE. 6. You can ALTER the NEXT SIZE of a TABLEs NEXT EXTENT. 7. EXTENT interleaving or FRAGMENTATION degrades performance. 8. tbcheck -ce reports when this degradation starts to hurt. 9. Minumum EXTENT size is 4 PAGES. 10. Maximum EXTENT size big (16,777,217). 11. Default EXTENT size is 8 PAGES. 12. The NEXT EXTENT is allocated when the current EXTENT is full. 13. EXTENT SIZES kinda double (nearest 20K) every 16 EXTENTS. 14. You can get rid of EXTENT interleaving (Fragmentation) in many of ways. 15. tbunload/tbload the db to compress EXTENTS. 16. ALTER <index> to cluster to physically re-organise the TABLE(EXTENTS). 17. unload/save schema/drop table/create table/load table works too. 18. There is a limit to the number of EXTENTS a TABLE can safely have. This is by no means a complete or guaranteed accurate list. I throw it open to the group as a basis for discussion. Perhaps the good people can take some time to critically look at this list and qualify it as there seems to have been quite frequent questions pertaining to EXTENTS in this group recently. Best Regards, Tom Hogarty <Standard Disclaimers Apply> Siemens Nixdorf Informationsystems Paderborn, Germany e-mail : hogarty.pad@sni.de