statistics (data)

External Article

Statistics on Ascending Columns

  • Article

It comes as rather a shock to find out that one of the commonest circumstances in an OLTP database, an ascending primary key with most querying on the latest records, can throw the judgement of the Query Optimiser to the extent that perfomance nose-dives. Fabiano Amorim once again dons snorkel and goggles to explore the murky depths of execution plans to find out why.

2011-09-16

2,528 reads

External Article

13 Things You Should Know About Statistics and the Query Optimizer

  • Article

Fabiano launches into a sound technical explanation of the way that the query optimiser works in SQL Server with a mention of Brazilian Soccer stars and young ladies on Copacabana beach. You'll never quite think of statistics, execution plans, and the query optimiser the same way again after reading this, but we think you'll understand them better.

2010-02-02

5,853 reads

Blogs

Advice I Like: Art

By

Superheroes and saints never make art. Only imperfect beings can make art because art...

Why Optimize CPU for RDS SQL Server is a game changer

By

One feature that I have been waiting for years! The new announcement around optimize...

Performance tuning KubeVirt for SQL Server

By

Following on from my last post about Getting Started With KubeVirt & SQL Server,...

Read the latest Blogs

Forums

The AI Bubble and the Weak Foundation Beam

By dbakevlar

Comments posted to this topic are about the item The AI Bubble and the...

data type gets lost in data flow

By stan

Hi, in a simple oledb source->derived column->oledb destination    data flow, 2 of my...

i noticed the sqlhealth extende event is on by default , so can i reduce

By rajemessage 14195

hi, i noticed the sqlhealth extended event is on by default , and it...

Visit the forum

Question of the Day

The Read Committed Snapshot Isolation behaviour

I am currently working with Sql Server 2022 and AdventureWorks database. First of all, let's set the "Read Committed Snapshot" to ON:

use master;
go

alter database AdventureWorks set read_committed_snapshot on with no_wait;
go
Then, from Session 1, I execute the following code:
--Session 1
use AdventureWorks;
go

create table ##t1 (id int, f1 varchar(10));
go

insert into ##t1 values (1, 'A');
From another session, called Session 2, I open a transaction and execute the following update:
--Session 2
use AdventureWorks;
go

begin tran;
update ##t1 
set f1 = 'B'
where id = 1;
Now, going back to Session 1, what happens if I execute this statement?
--Session 1
select f1
from ##t1
where id = 1;
 

See possible answers