Ghost Cleanup

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Ghost Cleanup

WayneS

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January 14, 2013 at 9:41 pm

#266983

Comments posted to this topic are about the item Ghost Cleanup
Wayne
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January 15, 2013 at 5:21 am

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Lokesh Vij SSChampion Points: 10836 More actions · Answer 1

Thanks Wayne. Got to learn something new today 🙂

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demonfox SSCertifiable Points: 6289 More actions · Answer 2

I got it right for wrong reasons ;

Learned something.. thanks for the question..

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SQLRNNR SSC Guru Points: 281334 More actions · Answer 3

Thanks Wayne

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okbangas SSChampion Points: 11773 More actions · Answer 4

As far as I understand it, there is something missing from the explanation. If we assume that only what's written in the scenario has happened, the scenario is as follows:

* Table is created

* Records are inserted

* Records are deleted -> Marked as ghost

* Ghost Cleanup Task is running (every 5 seconds).

But, there has not been any scan between the marking of ghost records and Ghost Cleanup Task, hence it has nothing to do.

The ghost cleanup task doesn't just start up when it's told to – it starts up in the background every 5 seconds and looks for ghost records to cleanup. Remember that it won't be told to go cleanup a specific page by a delete operation – it's a subsequent scan that does it, if a scan happens.

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Koen Verbeeck SSC Guru Points: 259085 More actions · Answer 5

Great question Wayne, thanks. Definately learned something.

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Stuart Davies SSCoach Points: 19505 More actions · Answer 6

Good question Wayne - thanks

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Carlo Romagnano SSC-Insane Points: 22597 More actions · Answer 7

Carlo Romagnano

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January 15, 2013 at 1:33 am

#1577174

Interesting!

Thanks!

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sqlnaive SSCoach Points: 17437 More actions · Answer 8

Great question. I needed to know. Lost a point but worth the knowledge.

Gazareth One Orange Chip Points: 27737 More actions · Answer 9

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January 15, 2013 at 2:55 am

#1577212

Nice question, thanks.

paul.knibbs SSCoach Points: 15320 More actions · Answer 10

okbangas (1/15/2013)
But, there has not been any scan between the marking of ghost records and Ghost Cleanup Task, hence it has nothing to do.

I think that's a scan that's carried out by the ghost cleanup task itself, not a random scan that's done as part of a SELECT statement. May be wrong on that, but that's how I read it!

mtassin SSC-Insane Points: 23099 More actions · Answer 11

Good question Wayne. Thanks!

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DugyC Hall of Fame Points: 3804 More actions · Answer 12

paul.knibbs (1/15/2013)
okbangas (1/15/2013)
But, there has not been any scan between the marking of ghost records and Ghost Cleanup Task, hence it has nothing to do.
I think that's a scan that's carried out by the ghost cleanup task itself, not a random scan that's done as part of a SELECT statement. May be wrong on that, but that's how I read it!

+1

Great question Wayne, thanks.

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Mighty SSCrazy Eights Points: 9063 More actions · Answer 13

okbangas (1/15/2013)
As far as I understand it, there is something missing from the explanation. If we assume that only what's written in the scenario has happened, the scenario is as follows:
* Table is created
* Records are inserted
* Records are deleted -> Marked as ghost
* Ghost Cleanup Task is running (every 5 seconds).
But, there has not been any scan between the marking of ghost records and Ghost Cleanup Task, hence it has nothing to do.

I agree with you that in this scenario the scan was not done, so nothing was done, but that is not relevant for the explanation: the page will never be completely deleted by the Ghost Cleanup Task, even if it would have been scanned before. As far as I can see that was the important lesson to be learned here.