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

► Complexity of the fetch. The fixed overhead saved for not having to go between the
database engine and the application program has a lower percentage impact for complex
SQL that has longer path lengths.
If the multi-row fetch reads more rows per statement, it results in CPU time improvement, but
after 10 to 100 rows per multi-row fetch, the benefit is decreased. The benefit decreases
because, if the cost of one API overhead per row is 100% in a single row statement, it gets
divided by the number of rows processed in one SQL statement. So it becomes 10% with 10
rows, 1% with 100 rows, 0.1% for 1000 rows, and then the benefit becomes negligible.
It turns out that the percentage improvement is larger when class 2 accounting is turned on,
because the cost of class 2 accounting which was encountered for each row fetched now is
encountered only for each multi-row fetch SQL statement. So the cost of class 2 accounting
would be dramatically reduced, for example, 100 times if fetching 100 rows in one multi-row
fetch SQL statement.
Multi-row insert performance
Figure 3-5 shows the CPU time (class 1) measurements for single-row insert and multi-row
insert of 100,000 rows into a non-partitioned table space.
Class 1 CPU Time (Sec)
4
3
2
1
0
Figure 3-5 CPU time (class 1) for single-row and multi-row insert
The measurements, compared to V7, show:
► For single-row fetch there is a reduction in CPU time when we compare the
measurements in V7 and V8 and insert requests.
► 35% CPU time improvement with MR=10 rows
► 40% CPU time improvement with MR=100+ rows
36 DB2 UDB for z/OS Version 8 Performance Topics
2.92
Multi-row Insert Performance
(100,000 rows Inserted / test)
Single-row V8 multi-row
2.73
2.51
V7 V8 50kx2 10kx10 1kx100 100x1k 10x10k
1.94
1.8
1.79
V8 with explicit multi-row Insert
50kx2 - 50,000 insert loops, 2 rows per multi-row insert
10kx10 - 10,000 insert loops, 10 rows per multi-row insert
1kx100 - 1,000 insert loops, 100 rows per multi-row insert
100x1k - 100 insert loops, 1,000 rows per multi-row insert
10x10k - 10 insert loops, 10,000 rows per multi-row insert
1.79