SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


Ghost Records


Ghost Records

Author
Message
Steve Jones
Steve Jones
SSC Guru
SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)SSC Guru (250K reputation)

Group: Administrators
Points: 250738 Visits: 19814
Comments posted to this topic are about the item Ghost Records

Follow me on Twitter: @way0utwest
Forum Etiquette: How to post data/code on a forum to get the best help
My Blog: www.voiceofthedba.com
Peter Trast
Peter Trast
UDP Broadcaster
UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)UDP Broadcaster (1.5K reputation)

Group: General Forum Members
Points: 1466 Visits: 655
First to answer and got it right! Never heard of it but the right answer was perfectly logical.

Great question!

Peter Trast
Microsoft Certified ...(insert many literal strings here)
Microsoft Design Architect with Alexander Open Systems
M&M
M&M
SSCrazy Eights
SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)SSCrazy Eights (9.7K reputation)

Group: General Forum Members
Points: 9748 Visits: 3916
I remember reading about this in an article.

M&M
khullargirish02
khullargirish02
SSC-Addicted
SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)SSC-Addicted (439 reputation)

Group: General Forum Members
Points: 439 Visits: 126
When rows are marked as deleted after a DML operation and the transaction is committed, the rows become Ghost records.

I got it right Smile
Kwex
Kwex
Say Hey Kid
Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)Say Hey Kid (683 reputation)

Group: General Forum Members
Points: 683 Visits: 240
Nice to know! DB2 behaves quite differently, because it just re-uses the page after records have been marked as deleted. It doesn't need an extra background process (ghost exorciser) to make a physical delete.

Not sure why SQL Server adopted this approach :-)

Kwex.
dave.clark
dave.clark
SSC-Enthusiastic
SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)SSC-Enthusiastic (123 reputation)

Group: General Forum Members
Points: 123 Visits: 567
I believe it is done for performance reasons. Deleting data can occur faster and rollbacks would be faster. Then a process can later update clear up the ghost records.
chrisfradenburg
chrisfradenburg
SSCarpal Tunnel
SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)

Group: General Forum Members
Points: 4384 Visits: 2084
As to why something goes through and cleans up the ghost records instead of just allowing the space get reused, that way the data doesn't remain on disk so it doesn't accidentally read by something. Or purposefully read by someone for that matter.
GilaMonster
GilaMonster
SSC Guru
SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)SSC Guru (417K reputation)

Group: General Forum Members
Points: 417176 Visits: 47141
cfradenburg (6/2/2011)
As to why something goes through and cleans up the ghost records instead of just allowing the space get reused, that way the data doesn't remain on disk so it doesn't accidentally read by something. Or purposefully read by someone for that matter.


Ghost cleanup doesn't overwrite the ghosted rows. A direct read of the data file can see deleted data well after the ghosted rows are removed.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass


chrisfradenburg
chrisfradenburg
SSCarpal Tunnel
SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)SSCarpal Tunnel (4.4K reputation)

Group: General Forum Members
Points: 4384 Visits: 2084
Interesting. What does the ghost cleanup process do then?
SQLRNNR
SQLRNNR
SSC Guru
SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)SSC Guru (111K reputation)

Group: General Forum Members
Points: 111840 Visits: 18624
GilaMonster (6/2/2011)
cfradenburg (6/2/2011)
As to why something goes through and cleans up the ghost records instead of just allowing the space get reused, that way the data doesn't remain on disk so it doesn't accidentally read by something. Or purposefully read by someone for that matter.


Ghost cleanup doesn't overwrite the ghosted rows. A direct read of the data file can see deleted data well after the ghosted rows are removed.


Sounds like a fun experiment...



Jason AKA CirqueDeSQLeil
I have given a name to my pain...
MCM SQL Server, MVP


SQL RNNR

Posting Performance Based Questions - Gail Shaw

Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum







































































































































































SQLServerCentral


Search