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Structure of pages DBTT pages
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7.4 DBTT pages
For each record type, UDS/SQL requires a table - known as the DBTT (Database Key
Translation Table) - in which all the currently stored records are administered via a database
key. Basically, this is an index in the DBTT which points to the physical address of the record
in the database as recorded in the table. The structure of the DBTT anchor pages and the
actual DBTT pages are described below.
7.4.1 DBTT anchor page
Only for the SSIA-RECORD there is no DBTT anchor page. For all other record types, the
DBTT is administered via DBTT anchor pages. The first DBTT- anchor page is recorded in
the SIA and shown in the output of utilty routine BPSIA. In order to manage the largest
possible DBTT for a record type - in a 4-Kbyte database this means more than 2 billion DB
keys - multiple chained DBTT anchor pages may be required. DBTT anchor pages are
located in the realm containing the DBTT. They are only set up in the length that is required
at the time of creation. In the great majority of cases, no more than one DBTT anchor page
is required for each record type. The DBTT itself consists of the DBTT base with a variable
number of DBTT pages and possibly DBTT extents each of which consists of 128 consec-
utive PAM pages.