Tag Archives: Oracle SQL tuning

Parallel query performance consistency

A collegue just asked me “didn’t you have a query to see what SQL has ran in parallel?” I’ve used this months ago and completely forgot, but this might come in handy again some day, so I’ll put this here. col … Continue reading

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Function based indexes sans the NULLs

A collegue asked my help with a performance issue. He was trying to tune a query that ran on a 6 TB table. The query had to return rows for a couple of specific statusses and for that it should … Continue reading

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Oracle performance mystery: wildly varying query response time

At this moment I’m working on a very weird performance issue on our Oracle Universal Content Management database. This is the query (actually with binds of course. Values for dReleaseState and dStatus are the same as far as I could … Continue reading

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Statistics history, revisited

Tuesday last week I did a presentation on the Planboard DBA Symposium in De Meern, the Netherlands, about SQL performance issues. The scope of my presentation was what to do when a SQL statement suddenly does not perform adequately. Often … Continue reading

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Planboard DBA Symposium: 17 juni 2014

Dutch-speaking readers of my blog might be interested to know I’ll be speaking at the 9th Planboard DBA Symposium at Oracle Nederland in De Meern. There will be (Dutch) sessions for DBAs and middleware specialists. I will do a session about first … Continue reading

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Useful stuff from event 10053 traces – part 2

I would like to reflect once more on the “dynamic sampling used for this statement” message. Suppose dynamic sampling really happened with reason, because statistics were old, missing or otherwise insufficient. Now what?   Dynamic sampling because of missing or old statistics … Continue reading

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Useful stuff from event 10053 traces – part 1

In theory you can use event 10053 traces to see what choices the optimizer has made, which is very interesting if your query didn’t perform as it was supposed to do. In practice event 10053 traces contain an overwhelming amount … Continue reading

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Dynamic sampling NOT used for this statement?

So I’m still working on this data warehousing project and performance is not quite optimal. There are all kinds of things to be investigated. One thing I want to find, is the reason why a lot of execution plans show … Continue reading

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Real World Performance Tour

Today I was in Breda, the Netherlands for the Real World Performance Tour, organized bij the Oracle Benelux Users Group. It is a day-long session by Andrew Holdsworth (Senior Director of Oracle’s Real World Performance team), Tom Kyte (who doesn’t … Continue reading

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A walkthrough through sqlperf 1.6 output (video)

I’ve made a video to walk you through the output of the sqlperf script version 1.6.

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