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How IDS Finds Data

The database tablespace is the table that tracks information about all the databases in the IDS instance. There is one row per database in this table, and each row contains columns which include the partnum for the systable for that database. Because partnum indicates the page in the tblspace tblspace that tracks information about that table. Part of that tracked data is the extent information for the table.

So how does IDS use this information? Consider SELECT * FROM mytab (in the eric database)

Database tblspace (partnum 0x00100002 is alway known)

dbs_namesystables partnumother cols

Use the partnum to find the page tblspace tblspace and go there to find the extents for systables

logical pagephysical page

Go to page 0x0010005D to find the beginning of the data for systables data Data page for systables table


Calculate the physical addres bassed on the partnum i.e. 20A of the tblspace tblspace for dbspace 1 Extent information on part.partn page for mytab

logical pagephysical page

42My Stuff 42
666My Stuff 666

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