AW: number of extents

Bill Hamilton asked: > Should I try to get the number of extents down on system tables? > Also, on automatic indexes, when should you worry about how many extents > they are in? Art S. Kagel responded: > Not to worry. All system catalog tables are cached in the data dictionary > cache so extent fragmentation in the catalog is not a problem since about > IDS 7.1. Christopher Coleman replied: > I hate to disagree, but I have seen secondary effects of too many extents. One is > that it can become impossible to drop a chunk because it has system catalogue > extents in it. There may also occasionally be a problem when the number of extents > causes other tables to become interleaved because they cannot get a sufficiently > large extent. > > These are not necessarily a huge performance impact, but they can be an administrative > problem. > The reason I want to bring this up is that there is not a good, safe way to compact > the system catalogue tables other than to drop and recreate the database, which is > not necessarily an option. There is another unpleasant side efect of many extents in system catalog tables. In IDS 7.31, a move from 32 to 64 may fail or an upgrade to 9.x or 10.x may fail. The reason is that during migration to 64 bit or upgrade to 9.x some structures on the partition page are changed (get larger) (where the extents are tracked). If the partition page is full of extents the enla In 7.31.[UTF]D1 and higher there is an unsupported feature in oncheck that allows the save extent reorg of system tables (not TBLSpace TBLSpace extents unfortunately) Unfortunatley this has never been documented and also never been forwarded to IDS 9.4 or 10. I have opened Feature request 156860 'ONCHECK -ME (MERGE EXTENTS) FEATURE IS MISSING IN 9.X SERVERS' but until now it has not been implemented . I heard rumours that is is going to be in IDS vnext . I hope it can be backported to IDS 10 or even 9.4 Regards Tilman Model-Bosch ------------------------------------------------------------------- <This information is provided AS IS etc, etc ... shall not be liable etc, etc....standard disclaimer :-)> sending to informix-list