[Okta Webinar] Learn how to a build a cloud-first strategyRegister Now

x
?
Solved

MS SQL Server, multiple threads reading the same table

Posted on 2010-11-12
5
Medium Priority
?
686 Views
Last Modified: 2012-05-10
I want to have two threads reading from the same table with different queries. I use ADO with C++.

Will this work? Any special magic required?
0
Comment
Question by:Z-Nerd
  • 2
4 Comments
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 34123242
no magic required, this shall work.

of course, if you try to read (or update) the same records, you will get some "locks" (so your code will get into wait), but for the rest, nothing
0
 

Author Comment

by:Z-Nerd
ID: 34123288
Why would two reads on the same record cause a lock? I understand if updating.
0
 
LVL 1

Assisted Solution

by:bclevlnd
bclevlnd earned 800 total points
ID: 34123724
You should use hints in your queries if you want sql to not lock records when selecting data.  That is the default behavior of sql.
Use:

select yourselection from yourtable with(nolock)

if you want no data locked.  You will, however, also be returned any dirty records.  You can use

with(rowlock)

to only lock selected rows, or

with(readpast)

to not return any dirty rows.
0
 
LVL 143

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 1200 total points
ID: 34126566
>Why would two reads on the same record cause a lock?

it depends on which transactional level the 2 sessions are.
if the 2 are in serializable mode, everything they touch in common will make the other one to wait on that same resource... because further down the transaction, a update might occur etc...

for single queries, there is no issue, though, as you say, they just will issue a read shared lock, and can both continue without actually blocking each other
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Hi all, It is important and often overlooked to understand “Database properties”. Often we see questions about "log files" or "where is the database" and one of the easiest ways to get general information about your database is to use “Database p…
SQL Server engine let you use a Windows account or a SQL Server account to connect to a SQL Server instance. This can be configured immediatly during the SQL Server installation or after in the Server Authentication section in the Server properties …
Please read the paragraph below before following the instructions in the video — there are important caveats in the paragraph that I did not mention in the video. If your PaperPort 12 or PaperPort 14 is failing to start, or crashing, or hanging, …
Is your OST file inaccessible, Need to transfer OST file from one computer to another? Want to convert OST file to PST? If the answer to any of the above question is yes, then look no further. With the help of Stellar OST to PST Converter, you can e…

834 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question