db2exfmt - Earlyout, Fetchmax, Iscan Operator

[Sam Durai]

Hello, When I use db2exfmt to generate the explain plan, under the
Operator section I can see the following arguments listed
[1] EARLYOUT
[2] FETCHMAX
[3] ISCANMAX
but I'm not sure what it means. Can someone share their experience
with these operators ?

[Serge Rielau]

Sam Durai wrote:

Hello, When I use db2exfmt to generate the explain plan, under the
Operator section I can see the following arguments listed
[1] EARLYOUT

Specifies that the operation doesn't have to be completed.
The most common example is EXISTS processing. No need to collect all the
rows in teh query. It's sufficient to find any.

[2] FETCHMAX
[3] ISCANMAX

Both related to prefetching. It limits how many rows are prefetched.
Usages include OPTIMIZE FOR n ROWS or FETCH FIRST n ROWS

Cheers
Serge
--
Serge Rielau
DB2 Solutions Development
IBM Toronto Lab