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Message Posted: Wed, 22 Jul 2009 @ 20:34:15 GMT

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"The diagnostic noprodjoin" is used to: disallow product joins for a particular session. This diagnostic, when set at the beginning of a session, will prevent the optimizer from using product joins in a particular query.

To turn on: (i.e. disallow product joins)

     diagnostic noprodjoin on for session;

To turn off: (i.e allow product joins)

     diagnostic noprodjoin not on for session;

Disabling product joins globally could be seriously detrimental to queries performance."

"It is NOT RECOMMENDED TO DISABLE PRODUCT JOINS globally unless it is for investigation purposes. If a query experiences performance problems due to some product join, that query needs to be investigated.

Regarding the pros and cons of disabling product joins on your Teradata system: Product joins are there for a reason, the Optimizer sometimes decides that they are more efficient than any other type of join. If that is not true in some cases, that can be due to either incorrect estimates, skewed data or possibly Optimizer bug. Each query needs investigated individually.

Best regards,

Wale

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