The optimizer HINT that rules them all!

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There are many optimizer hints that can be used to change the performance of a query. But there is an optimizer hint that does NOTHING to the performance yet is easily the most important hint you'll ever use in a SQL statement.
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Опубликовано:

5 фев 2023

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Комментарии : 9

@nagarajuneeriganti8101 Год назад

Thank you. Very informative and useful...

@iyadahmed3773 Год назад

Very great analogy!!

@DatabaseDude Год назад

thank you!

@berndeckenfels Год назад

Does it do more than tally the numbers (I.e. refreshes statistics or caches the results)? Can statistics_level=all on the session do the same without hints?

@DatabaseDude Год назад

stats_level all will do the same job, but of course, now you're getting the measurement on *every* query in that session

@vikram4755 Год назад

Nice and useful, doesn't this add an overhead to the query execution on the very first run? As the consecutive runs will be quick as optimisor now has all the statistics

@DatabaseDude Год назад

there will be a parse overhead. I'm not recommending you have this hint in your apps, just for diagnosis

@davidmoore4567 Год назад

Does running 19c on Exadata with autonomous database add this hint automatically to the first execution of every DML statement unless statistics were already gathered recently.

@DatabaseDude Год назад

no. but if you set statistics_level = all, we collect the same data