Query tuning by waste minimization: a real-life example

Today I’d like to share another tuning example from a recent case at work, which in my opinion is good for illustrating typical steps involved in SQL optimization process.

I was handed a poorly performing query with a relatively verbose text, so I will only give the general structure here (it will also prevent me from accidentally disclosing some sensitive information from that application):

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Log buffer space


Log buffer space is a simple, yet frequently misunderstood wait event. The main reason for that is probably its name. It sounds as if it points immediately to the answer: if space in the log buffer is the issue, then increasing it surely should resolve it. Well, unfortunately even though log buffer space is simple, it’s not that simple.
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