Can custom/manually built projections degrade Query performance

Rajashekar_Dasa

We have created new Projections for some of the tables. Just wanted to check, If our projections can degrade the query performance ?

knicely87

Sure they can! But are your queries using the created projections? Check with the EXPLAIN command. There is also a PROJECTION_USAGE system table that you can query to see what projections are being used.

Rajashekar_Dasa

Thanks for your reply ...we are building it test environment. Projections were built assuming some of the customer use csses . These newly built projectuons are used .but not sure on production environment, if they will be picked . Therfore wanted to check ; can we say wrongly designed peojectiin can cause degrade in performance. Can wrongly designed projection cause hash joins over merge joins ? What is check list or criTeria to state if The projection is good or bad? ..if its just case of noT be used , we are ok ..if it causes Performances degrade that is what i want to avioD