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May 202013
May 162013
Both system functions, Len() and DataLength(), in SQL Server are used to measure the length of the data. The main difference of those 2 is that Len() gets the string length of the data in which DataLength measures the storage length of the data.
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May 142013
I blogged DBCC WritePage a year ago here http://www.sqlnotes.info/2011/11/23/dbcc-writepage/. It’s an extremely dangerous command especially with the last parameter “directORbufferpool” of this command turned on. I also showed you how to fix the page checksum here http://www.sqlnotes.info/2013/05/02/fix-page-checksum/. To protect yourself, please ensure you are operating on the database that you want, not system databases. Taking a full backup before playing this command is important. Never run it in your production. Beside that, there is a simple way to rollback changes made by DBCC WritePage…
May 092013
In my last post, I demonstrated how to mount a database with missing NDF files. In the end, we still have issues removing tables created over missing files, the files are taken offline. Be cautious of taking files offline since there is no (official) way to bring it back online. In either situation, you will need to modify/correct SQL Server metadata. This is allowed in SQL Server 2000 with “Allow ad hoc update” option turned on. However, it’s deprecated in SQL Server 2005 and removed in SQL Server 2008 and upper versions.
May 072013
I wonder if you’ve had the situation that I had before where you have to attach a database with one or few missing .ndf files. It seems pretty common since I’ve just seen the same scenario at one of my clients. The reasons behind it are quite similar – They created a new file group with files to host some temporary data for data fixing or testing. New files were not created under the folder as usual and they thought they would remove them right after tasks complete. But the latter part got forgotten afterwards.
May 022013
A checksum value is tagged with every data page in SQL Server. This is used to detect issues on the storage system to ensure what has been read from the disk is what has been written to the disk. When the checksum is detected which is not the one it’s supposed to be, the page will not be read into the buffer pool. SQL Server will return error. If you are sure the data on the page are all correct or the checksum is broken purposely, you do have the option to fix it even you don’t know how to calculate it.
Apr 302013
This is a very interesting error happened in one of my clients’ databases. Their database has been running for at least 12 years without a single problem. They run DBCC CheckDB regularly to ensure the database is in healthy state until few days ago their DBA ran DBCC CHECKTABLE with data_purity and get
Msg 2570, Level 16, State 3, Line 1 Page (1:118), slot 0 in object ID 245575913, index ID 0, partition ID 72057594039042048, alloc unit ID 72057594043432960 (type "In-row data"). Column "Value" value is out of range for data type "numeric". Update column to a legal value.
Finally, they found this article, , http://support.microsoft.com/kb/923247. — Many things can cause this kind of error. In this blog post, I am going to demo how I repeat and fix this error — for fun.
Jan 252013
What’s a SQL Saturday
FREE, all-day, educational event focused on Data related Topics
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Jan 092013
SQL Saturday 198, http://www.sqlsaturday.com/198/ ; is coming to Vancouver Feb 16 this year. As of now, 56 sessions are collected from 30 speakers, http://www.sqlsaturday.com/198/schedule.aspx?sat=198. Curiously last night, I pulled all speakers from the list and concluded that it will be a great event this time.
- 19 SQL MVPs
- 7 author/co-authors
- 4 MCMs
- 4 PASS User Group Leaders
- 3 MS Employees (One of them is program manager of SQL Cloud infrastructure team)
- 2 former MS employees (one of them was former MCM program manager)
- One from NetApp
- One PhD
Join us and enjoy the sessions.
Dec 262012
We know that we need to take special attention about NULL values while writing queries because they may lead us into writing incorrect query logics. NULLs may also affect the performance of aggregation function MAX() and MIN(). I have submitted this issue to Microsoft Connect. There are number of ways to get around it. I think the improvement can also be done at query engine level. Hope this can be fixed in next or future version of SQL Server. But for now, we need to know it and know how to get around it.