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Null Quiz
Here’s an example I saw a few months ago of the confusion caused by NULL. As the owner of the problem put it: the first query, run from SQL*Plus for testing purposes, takes no time to complete; but...
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Random slowdown
One of the old, old questions came up on OTN a few days ago: “What reasons are there for a piece of (batch) SQL to run very slowly occasionally when it usually runs very quickly ?” Then a similar one...
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Troubleshooting
If it’s a long night, and you’ve got nothing better to do waiting for the new year, then here’s some reading to keep you entertained. A collation of Tanel Poder’s trouble-shooting blog postings, dating...
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LOB changes
It’s always useful to collect baseline information – especially when it helps you notice that the baseline has moved in a way that might explain the next performance problem you see. Here’s an example...
View ArticleMaster Note: Database Performance Overview (Doc ID 402983.1)
Purpose Questions and Answers Pro-Active Problem Avoidance and Diagnostic Collection Performance Information Centres Troubleshooting Guides Common Problem Topics Slow Database Performance Concurrency...
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Pagination
I was involved in a thread on Oracle-L recently started with the question: “How many LIOs is too many LIOs”. Rather than rewrite the whole story, I’ve supplied a list of links to the contributions I...
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Clustaghhh!
It doesn’t matter which bit of Oracle technology you want to use, eventually someone, somewhere, runs into the special case where something nasty happens. Here’s an edge case for people using (index)...
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Minus
Here’s a little script to demonstrate an interesting observation that appeared in my email this morning (that’s morning Denver time): Clearly the first query block in the test query will return no...
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RAC Plans
Recently appeared on Mos – “Bug 18219084 : DIFFERENT EXECUTION PLAN ACROSS RAC INSTANCES” Now, I’m not going to claim that the following applies to this particular case – but it’s perfectly reasonable...
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Row Migration
At one of the presentations I attended at RMOUG this year the presenter claimed that if a row kept increasing in size and had to migrate from block to block as a consequence then each migration of that...
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