NOLOCK is a SQL Server table hint, equivalent to READUNCOMMITTED. It applies READ UNCOMMITTED isolation level semantics to the hinted table.

learn more… | top users | synonyms

3
votes
2answers
396 views

Why is WITH NOLOCK running as Serializable

I ran the following query: SELECT session_id,CASE transaction_isolation_level WHEN 0 THEN 'Unspecified' WHEN 1 THEN 'ReadUncommitted' WHEN 2 THEN 'ReadCommitted' WHEN 3 THEN 'Repeatable' WHEN 4 ...
1
vote
1answer
79 views

SELECT Causes Performance Issue [closed]

I have a SQL SELECT statement that has joins on 27 of our warehouse tables. Original statement was taking more than an hour everyday so I decided to optimize it. I created some indexes but still it ...
9
votes
1answer
130 views

How to reproduce “Could not continue scan with NOLOCK due to data movement”

I occasionally get "Could not continue scan with NOLOCK due to data movement" with some large jobs, which do have WITH (NOLOCK) on the select queries. I understand this has something to do with ...
2
votes
0answers
142 views

Table queries locked during long insert SQL server

Everyday runs a sql job that loads data from bulk files and load them in auxiliary tables, to adapt and then copy to the destination table where applications read (and only read) the data. I am ...
4
votes
1answer
3k views

Use NOLOCK hint when calling table valued function

Suppose the following function: CREATE FUNCTION [dbo].[ufnTest]() RETURNS TABLE AS RETURN SELECT 1 AS Nr My actual function will select actual data from many different tables. I (mostly) understand ...
0
votes
0answers
100 views

NOLOCK hint on a table that is 100% reads?

I have tables that during production hours are not wrote to, and yet during the night they can have records written. The few nights data is being wrote to the tables, users are not running queries ...
2
votes
3answers
982 views

SQL Server data extract with limited performance impact

Background: I have a SQL Server 2008 Enterprise Edition database containing three tables. The tables contain ~3 million, ~14 million, ~14.5 million rows respectively. Problem: I need to do a data ...
0
votes
1answer
635 views

Deadlock : Behaviour of NOLOCK

We are running into deadlocks when we run concurrent instances of following query : BEGIN TRAN IF NOT EXISTS (SELECT TOP 1 * FROM Table1 WITH (NOLOCK) WHERE Col1 = Val1 AND Col2 = Val2) BEGIN ...
3
votes
1answer
1k views

Execution of sequential delete and uncommitted read

We are running the following queries using dynamic SQL, which is erroring out for few cases when we run concurrent instances. The error is: Could not continue scan with NOLOCK due to data ...
4
votes
1answer
170 views

repeatable read and nolock

Does anyone know what the net effect of having a block of t-sql with a transaction isolation level of repeatble read and then inside having a select with nolock. Does the nolock become invalid ...
3
votes
2answers
4k views

Can someone explain why select with nolock will query a potion of updated data?

I was reading the answer from here (from stackoverflow, I think should ask in here) NOLOCK means placing no locks at all. Your query may returns portions of data as of before UPDATE and ...
27
votes
4answers
3k views

Is NOLOCK always bad?

I am a Report Developer who wants to make my queries as efficient as possible. I used to work with a DBA who told me - I believe because I was always dealing with reports on a Production Server - to ...
8
votes
2answers
19k views

Could not continue scan with NOLOCK due to data movement

We run SQL Server 2000 and we get a few of these errors every night. Could not continue scan with NOLOCK due to data movement The query that throws this error is a large complex query that joins ...
18
votes
3answers
4k views

Justify NOT using (nolock) hint in every query

Have you ever had to justify NOT using a query hint? I am seeing WITH (NOLOCK) in every single query that hits a very busy server. It is to the point that the developers think it should just be on ...