DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

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Figure 5-12 FETCH CPU time - Alter index not padded and rebind
The FETCH CPU time after rebind shows no difference compared to an originally created
NOT PADDED index. Also an index-only access path is used after rebind.
A second test was run with a set of 15 queries doing joins on two VARCHAR(10) columns.
The join columns are accessed via matching index scan. We measured the query
performance for this set of queries using padded keys. Then we altered the indexes to NOT
padded, ran rebuild index and RUNSTATS and measured the query performance for 15
queries using not padded keys. We repeated this test with VARCHAR(20) and VARCHAR(30)
columns. In Figure 5-13 we show the CPU overhead using NOT PADDED indexes vs.
PADDED indexes.
238 DB2 UDB for z/OS Version 8 Performance Topics
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CPU time (microseconds) Fetch CPU time …Alter Index Padding
padded padded => rebind not padded not padded
ix not padded program => padded ix
Fetch CPU time reduced after application program rebind
- access path changed to index-only access