Cost Based Optimizer Settings

Siebel uses Cost Base Optimizer and will set the following DB Parameters while executing any query.

For Oracle 9i
alter session set optimizer_mode = first_rows_10
alter session set hash_join_enabled = false
alter session set “_optimizer_sortmerge_join_enabled” = false
alter session set “_optimizer_join_sel_sanity_check” = true

For Oracle 10g
alter session set optimizer_mode = first_rows_10
alter session set “_optimizer_sortmerge_join_enabled” = false
alter session set “_optimizer_join_sel_sanity_check” = true
 
Setting these parameters is required to get consistent results.
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