Reading SQL Server's Transaction Log

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Reading SQL Server's Transaction Log

Kraig Kerr

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November 20, 2010 at 2:06 pm

#243073

Comments posted to this topic are about the item Reading SQL Server's Transaction Log

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TRACEY-320982 SSChampion Points: 13653 More actions · Answer 1

With this information would you be able to replicate the data to another database. Most of the software we use does not have primary keys so SQL Replication is not an option.

Mirroring, snapshots not an option as the reporting database needs to be up 24 /7 and not down whilst snapshots run or log transactions are built on the reporting database.

Just curious

Kraig Kerr SSC Enthusiast Points: 190 More actions · Answer 2

Do the tables in question have any clustered indexes? If not you'd be dealing with "Heaps" and your only recourse would be to run a whole lot of DBCC Page commands or explore using %%phyloc%%. [/url]

Also dealing with updates is a lot more complex than dealing with inserts.

faboudib SSC Veteran Points: 268 More actions · Answer 3

Nice article,

However, would you mind specifying on which versions of Sql Server this works? If this works only on Sql Server 2000, and that is your target platform, you might want to look into RedGate's free product SQL Log Rescue (http://www.red-gate.com/products/SQL_Log_Rescue/index.htm) for similar functioanlity. Otherwise great work...

Regards,

Lowell SSC Guru Points: 323504 More actions · Answer 4

I believe the target schema is 2008; it worked just fine for me...the object id of my table was actually exactly the same as the article.

in 2005 Express, i get a couple of minor syntax issues, but after i look deeper, i'm sure it'll be obvious what to tweak.

Thanks for the great article.

faboudib (11/22/2010)
Nice article,
However, would you mind specifying on which versions of Sql Server this works? If this works only on Sql Server 2000, and that is your target platform, you might want to look into RedGate's free product SQL Log Rescue (http://www.red-gate.com/products/SQL_Log_Rescue/index.htm) for similar functioanlity. Otherwise great work...
Regards,

Lowell

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Mike C SSC-Insane Points: 23224 More actions · Answer 5

I'd like to stress a point the author mentioned in passing: this function is UNDOCUMENTED. What does that really mean? Well, to summarize:

1) Microsoft does not support the function. If you run into issues in production with this function, the first solution you will probably get is to remove the dependency on this function. Apart from that you're probably pretty much on your own.

2) It could have undesirable side effects. Blocking comes immediately to mind for this function.

3) It may not be available/accessible in the next release. That is, it can be pulled at any time, including major release, minor release, or even service pack. Sp_makewebtask anyone?

You mentioned Paul Randall, Kimberly Tripp and Isaac Kunen in your article, but I've never seen a recommendation from them to use this in production. Every time I've seen them use this it has been to demo one-off troubleshooting. You may want to clarify this before people start asking how they can use this to do things like create their own transaction log monitoring or home-baked custom replication systems in production environments. Nobody wants to waste money on a CSS call only to find out the code they've written using undocumented functionality is not supported.

Francis Apel SSC Eights! Points: 918 More actions · Answer 6

Nice Article.

Thank you for taking the time to lay this out.

Francis
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SQLRanger.com

knoopix Valued Member Points: 67 More actions · Answer 7

knoopix

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Points: 67

November 22, 2010 at 7:40 am

#1253739

Very nice article ! Waiting the next one now 😉

Phil Brammer Ten Centuries Points: 1135 More actions · Answer 8

However, if our table had been a HEAP this method works nicely because the data remains with the [Page ID] and [Slot ID] for the life of the HEAP.

That's not quite correct. Data will move in heaps and hence change page numbers. Updates to rows that cause the row to no longer fit on the page will cause it to move. When this happens a forwarding pointer is left in the original page, pointing to the new page. ALTER TABLE ... REBUILD will also renumber your pages and allocation_unit_ids.

Phil Brammer Ten Centuries Points: 1135 More actions · Answer 9

The link to the MGM Mirage article does not work. I'm still trying to decifer what your reasons for reading the log are. Also, what version of SQL are you using for this demo?

Phil Brammer Ten Centuries Points: 1135 More actions · Answer 10

DBCC PAGE is undocumented as well. Use at your own risk.

dma-669038 SSCrazy Points: 2773 More actions · Answer 11

Yes that was my thought too, lot of very detailed research and very well written, but what practical use would you put this to?

rbaskett SSC Enthusiast Points: 168 More actions · Answer 12

rbaskett

SSC Enthusiast

Points: 168

November 22, 2010 at 11:03 am

#1253901

SRD?

Kraig Kerr SSC Enthusiast Points: 190 More actions · Answer 13

Looks like TDWI took down that link. Here is another that points to the same article. http://findarticles.com/p/articles/mi_m0EIN/is_2000_Nov_8/ai_66696495/

The current flavor of this works with SQL 2008, but with minor changes will work with SQL 2005. I also have a version for SQL 2000. I should have specified this in the article, thanks for the catch.

Kraig Kerr SSC Enthusiast Points: 190 More actions · Answer 14

Systems Research & Development (SRD) founded by Jeff Jonas.