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Status Under review
Workspace Db2
Created by Guest
Created on Dec 12, 2023

Parameter 'PCTFREE FOR UPDATE' in Db2 LUW similar to Db2 z/OS

in Db2 z/OS there is a 'PCTFREE FOR UPDATE' parameter. We will need a similar parameter for Db2 LUW.

Background:

Our datawarehouse application 'IDH' uses many Bi-Temporal tables.  An update of any row in the source system will lead to the logical termination of the old row (lowering the upper interval limit of business-time to the current date => UPDATE) and INSERT of a new row with current values.

We assume, that the new inserted DATE,  when performing an UPDATE of the row, will make the new value  a bit longer (maybe because the new date cannot be compressed as well as before: usually = 9999-12-30, identical for many rows).

The defined PCTFREE will now be used up quickly, by the many INSERTS taking place, implicitly caused by the UPDATES causing overflows.

 With an additional option 'PCTFREE FOR UPDATE' there would be the possibility to reserve a part of free space, to avoid overflows.

 Reference:

The docu for 'CREATE TABLE' statement says: 

PCTFREE integer
Specifies the percentage of each page that is to be left as free space. The first row on each page is added without restriction. When additional rows are added to a page, at least integer percent of the page is left as free space. The value of integer can range from 0 to 99. A PCTFREE value of -1 in the system catalog (SYSCAT.TABLES) is interpreted as the default value. The default PCTFREE value for a table page is 0.

The docu for SYSCAT.TABLES states: 
PCTFREE SMALLINT Percentage of each page to be reserved for future inserts.

 

Needed By Quarter