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

3.1 Multi-row FETCH, INSERT, cursor UPDATE and DELETE
When using multi-row fetch operations, available in NFM, you normally fetch a set of rows, or
a rowset in a single fetch operation, as shown here in the case of 10 rows:
FETCH NEXT ROWSET FROM my-cursor FOR 10 ROWS INTO :hva1, :hva2, :hva3
Figure 3-1 shows the advantage of dealing with rowsets.
SQL
Declare
Cursor
Open
Cursor
Fetches
Close
Cursor
Commit
Single-row Fetch vs. Multi-row Fetch
APPL DBM1 MSTR IRLM
SQL
Declare
Cursor
Open
Cursor
Fetches
Close
Cursor
Commit
Figure 3-1 Multi-row fetch reduces the trips across the API
APPL DBM1 MSTR IRLM
Since DB2 now fetches 10 rows in a single Application Program Interface (API) crossing
(going from the application to DB2 and back), instead of 10 API crossings, one for each row
fetched without rowsets, multi-row fetch reduces the multiple trips between the application
and the database engine. This reduction produces even more benefits in distributed
applications, see 7.2, “Multi-row FETCH and INSERT in DRDA” on page 285.
Characteristics of multi-row fetch:
► Multi-row fetch eliminates multiple trips between the application and the database engine
► Multi-row fetch enhances the usability and power of SQL
► A single fetch statement using multi-row fetch can retrieve multiple rows of data from the
result table of a query as a rowset
► Rowset is the set of rows that is retrieved through a multi-row fetch
Characteristics of a rowset cursor:
► A rowset cursor is a cursor which returns one or more rows for a single fetch statement
► Each row in a rowset can be referenced in subsequent cursor-positioned UPDATE and
DELETE statements
Chapter 3. SQL performance 31