- Processor scheduling
- Memory management
- Network
- Disk I/O
Friday, September 29, 2017
Transitioning of SQLOS to SQLPAL
Monday, June 19, 2017
How to fix cardinality estimation anomalies [Video]
Tuesday, May 23, 2017
Understanding Skewed Data in SQL Server
My latest article. http://bit.ly/2qd4rtl
bit.ly Introduction I recently did some research to analyze skewed data distribution in SQL Server. This article is the outcome of my analysis to share with SQL Server community. SQL Server understands its data distribution using statistics. The SQL Server query optimizer then uses the statistics to calculate estimated row counts when executing the queries submitted … |
Monday, April 24, 2017
How to get all SQL Server internal tasks
Wednesday, April 19, 2017
SQL Server 2017 becomes the first commercial RDMS with built-in AI support
Wednesday, April 12, 2017
How To Generate In-Memory OLTP Migration Checklist
- Connect to the server in SSMS.
- Right-click on the database and select Generate In-Memory OLTP Migration Checklist option. (See below screenshot)
- Click Next on the first page of the wizard.
- In Choose Objects screen, you can select the tables, stored procedures or both. You also can specify a location for the checklist to be saved. Then click on Next. (See below screenshot)
- In Summary page, you can generate the PowerShell script for this task. This is optional. Click on Finish.
- It takes some time depending on the number of objects (tables, triggers, foreign keys, indexes, stored procedures, etc) in the database. Because it checks all the dependent objects against the In-Memory OLTP rules.
Monday, April 10, 2017
Sharding implementation in SQL Server
Sunday, April 9, 2017
Incredibly large memory support in Windows Server 2016
Thursday, March 30, 2017
Developer Friendly T-SQL Enhancements in SQL Server 2016 and vNext
- CREATE OR ALTER
- DROP IF EXISTS
Tuesday, March 28, 2017
Why use SELECT * With DMVs?
Monday, March 27, 2017
SQLSaturday584 - Colorado Springs
Another great SQLSaturday conference ended on 25th March, 2017 at Colorado Springs. I presented SQL Server Statistics and New CE model. You can visit the below link to download the presentations and demos which you’re interested. There are many valuable topics.
Thanks everyone who participated for the event!
Tuesday, March 7, 2017
SQL Server errors are too generic
Below is an actual error captured in SQL Server Error log during an incident.
This error is not quite accurate because it says SQL Server must shut down in order to recover a database which is database id 1. In SQL Server, database id 1 means "master" database. The next statement says the database is either a user database or system database. In this particular case, it can not be a user database.
The error message is quite generic. It appears that SQL Server does not change the error messages depending on the database id in this case, maybe it could be due to a performance impact.
Monday, February 27, 2017
Understanding SQL Server backups
One of my friends and colleagues (Jayaruwan alias JB) recently asked me a question regarding SQL Server backup. The question was, during the backup operation, what will happen to the data changes? Are those data recorded in the backup? If so till what point?
I knew for a fact that the data changes during the backup operation will get written to the backup. To demo this, I did the following test.
You need to open two query windows in SSMS. In this demo, I used SQL Server 2016 and bit large sample database named, AdventureWorksDW2016CTP3.
To run the demo yourself, you can follow the below steps.
Open two query windows in SSMS and copy and paste the below code in each query window.
--Window 1
--part 1
USE AdventureworksDW2016CTP3;
GO
DROP TABLE IF EXISTS backuptest
GO
CREATE TABLE backuptest
(
Id int identity(1,1) primary key,
Test_Desc varchar(1000)
)
GO
--part 2
DECLARE @msg3 binary(128);
SET @msg3=CAST('Kick off the full backup of AdventureworksDW2016CTP3' AS binary(128));
WHILE 1=1
INSERT INTO backuptest (Test_Desc)
SELECT command + ' ' + CAST(percent_complete AS varchar) + ' ' + CONVERT(varchar, GETDATE() ,121) FROM sys.dm_exec_requests
WHERE context_info=@msg3;
GO
--part 3
USE AdventureworksDW2016CTP3
GO
SELECT * FROM backuptest
--part 4
USE master;
Copy and paste the below code snippet in the 2nd Window.
--Window 2
--part 1
USE master;
GO
DECLARE @msg3 binary(128);
SET @msg3=CAST('Kick off the full backup of AdventureworksDW2016CTP3' AS binary(128));
SET CONTEXT_INFO @msg3;
PRINT 'Backup Database Started at : ' + CONVERT(varchar, GETDATE() ,121);
BACKUP DATABASE AdventureworksDW2016CTP3 TO DISK='C:\temp\AdventureWorksDW2016CTP3_full.bak'
WITH INIT;
PRINT 'Backup Database finished at : ' + CONVERT(varchar, GETDATE() ,121);
GO
--part 2
RESTORE DATABASE AdventureworksDW2016CTP3 FROM DISK='C:\temp\AdventureWorksDW2016CTP3_full.bak'
Execute the Part 1 and part 2 queries in Window 1.
Immediately move to the window 2 and execute the part 1. Watch the execution of the second Window, which is BACKUP DATABASE statement and once it's completed, you need to stop the execution of Query Window 1.
You need to copy and paste the result of the backup operation which is similar to the following.
Backup Database Started at : 2017-02-27 22:21:58.270
Processed 186680 pages for database 'AdventureworksDW2016CTP3', file 'AdventureWorksDW2014_Data' on file 1.
Processed 39 pages for database 'AdventureworksDW2016CTP3', file 'AdventureWorksDW2014_Log' on file 1.
BACKUP DATABASE successfully processed 186719 pages in 14.817 seconds (98.450 MB/sec).
Backup Database finished at : 2017-02-27 22:22:13.200
It has the information of what time the backup started and what time it finished.
Now, you can check the data in backuptest table by executing the part 3 of the query in Window 1. See below figure for sample data set;
You can notice there are many rows inserted along with the percent completed of the backup statement which executed in parallel to the BACKUP DATABASE statement in Query Window 2. For later reference, copy and paste the result set to an Excel sheet. After carefully observing the data set, you need to change the database to master in Query Window 1 (part 4)
At this point, you've a full backup file in the local directory and we know that while the backup operation in progress we inserted the data to a table in Query Window 1.
Now switch back to the Query Window 2 and restore the database using the part 2. Upon completion of the restore, observe the data in backuptest table using part 3 of the Query in Window 1.
You can notice, most of the data changes happened during the backup process is still there. See the below figure;
The last entry recorded in the table is “BACKUP DATABASE 99.9967 2017-02-27 22:22:13.060”. At that point, database backup statement is completed 99% and the time is 22:22:13:060. We also have the backup statement completed time which is, “2017-02-27 22:22:13.200”. So actually it has missed 140 milliseconds worth of data.
You can do this demo yourself and get more understanding.
Cheers!
Monday, February 20, 2017
SQLSaturday582 - Melbourne
How to interpret Disk Latency
I was analyzing IO stats in one of our SQL Servers and noticed that IO latency (Read / Write) are very high. As a rule of thumb, we know tha...
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Sharding is a data partitioning technique which is popular in NoSQL databases like MongoDB and Cassandra. You can scale out the data set h...
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This post is for SQL Server Database Administrators who have find difficulty in some situations when identifying slow running queries. The D...
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This can happen due to many factors like lack of indexes, out of dates statistics, if it returns a large number of records, etc. I observed...