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Diff between ALL_ROWS & CHOOSE [message #59178] Sun, 02 November 2003 22:22 Go to next message
Daljit Singh
Messages: 290
Registered: October 2003
Location: Texas
Senior Member
Hi,

Can anybody explain me the difference between these two optimizer modes : ALL_ROWS and CHOOSE.

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Re: Diff between ALL_ROWS & CHOOSE [message #59187 is a reply to message #59178] Mon, 03 November 2003 05:35 Go to previous message
Thiru
Messages: 1089
Registered: May 2002
Senior Member
Daljit,

CHOOSE will go for Cost based optimizer when atleast one of the tables involved in the sql statement is analyzed.And by default the Cost based optimizer will try to device an execution plan with the goal of best throughput(ie ALL_ROWS). In the absence of any statistics CHOOSE will choose RULE based optimizer.

By setting optimizer_mode=All_Rows , you are forcing the optimizer to go for CBO,with the goal of best throughput, with or without any statistics.

Also see the following demo :

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