Re: Tblspace Tblspace/Dbspace bit map page

Sadagopan, Sathish wrote: > > Hi, > > What is the difference between the Tablespace Tablespace bit-map page and > the Dbspace bit map page ? Why the hell are you interested in such a tender subject ? Don't you agree that this stuff is only necessary for incurable nerds ? > Is it that the Tblspc.Tblspc. bit map page is only for the pages containing > the Tblspc.Tblspc and the DBspc. bit map page for the free pages containing > data ? ( I have no idea of what I am talking about ) The well known Bitmap Pages manage the contents of the extents of tablespaces ( let's say tables ). You will find an initial Bitmap Page at the beginning of the first extent of a table. Since version 7.2 the server is only using so called 4-Bit Bitmap Pages - in earlier versions they used also 2-Bit Bitmap pages for tables without special columns ( text, byte, varchar ) and a row size less than a page. The 4-Bit Bitmap Page contains informations about the page type and the used space. Additional Bitmap Pages are also tracked in the Bitmap Page. A hex value of 0x8 indicates either an index page or a bitmap page. Depending on the position of the hex value you can determine whether this is a bitmap or an index page. The Tablespace Tablespace is a special table but it is also made up of extents. Initially Informix allocates 50 pages in each dbspace for the tablespace tablespace ( the 1st extent ). The first page of this extent is the Tblspace Tblspace Bitmap Page. Because you can drop and create tables, this table acts like an ordinary table and it makes sense to track free and full pages by Bitmap Pages. > When i look into the oncheck -pT output , which shows a certain number of > bit map pages for the tablespace.So if the usage of the tablespace (NOT > Tblspc.Tblspc) is described in the Tblspc.Tblspc. bit map page , then what > does the Dbspace bit map page contain. I guess a Tablespace Tablespace Bitmap Pages does not track remainder- and blob pages, but I'm not sure. Try to find out the contents of both Bitmap Pages by using oncheck -pp and the following overview of the bits: 4-Bit Description 0000 Unused Page 0100 Home Data Page (not filled) 1000 Index or Bitmap Page 1100 Home Data Page (filled) Remainder Pages and Blob Pages contain different values. > The manuals are not very clear on this.I know i am missing something here. > Could someone explain. > > TIA > Sathish Sadagopan Bye Stefan Weideneder PS: Next time we certainly should discuss "Partition Blob Pages" :-)