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Expert Topic: what locking do you use?

Posted on 2011-02-22
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Last Modified: 2012-05-11
Following the example of http:Q_26838925.html :

This discussion is intended for Experts working with SQL Server , and is focused on locking and cursors.

In your development, do you use anything other than client-based cursors?
Do you regularly use transactions?
If you do, how do you achieve it in the development tools?

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Question by:Vadim Rapp
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Expert Comment

by:Qlemo
ID: 34953800
We use (VS) C++ and ADO with server-based cursors (forward-only and static). It can be assumed forward-only runs as client-based cursor.

Transactions are opened by switching the transaction isolation level of the connection from "read uncommitted" or "read committed" to "repeatable read". Repeatable read prevents updates on read records.
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by:Vadim Rapp
ID: 34953933
What is user B wants to update a record locked by user A who just has left for lunch?
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Expert Comment

by:Qlemo
ID: 34953976
NEVER let a transaction open for longer than a few seconds. If you read records to present them in a GUI, or require any other user interaction, you do that without locking. As soon as you want to update, you either need to check yourself if the record (or specific value) has been changed meanwhile, or force-update, loosing all changes performed by other users.

BTW, sure you only want to spend 50 points here?
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by:Vadim Rapp
ID: 34954078
If I'm not mistaken, this is pretty much how client-based cursor works. When it uploads the data, it of course does place some locks anyways.

Re. 50 points - as I posted in the 1st post, it's an inter-expert discussion, for those who are interested. It's not that anybody needs an assistance in resolving a problem.
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Qlemo earned 200 total points
ID: 34954382
You are correct with the client-based cursor - at least in part. The cursor might still do (forward) paging, and hence locking the records of the page actually worked on.

And no - it does not work that way. A client-cursor needs to be considered as a read-snapshot. In a fully integrated GUI solution, like a datagrid, only the current record is locked (if at all). Changing the row will save.
Another approach used with ADO.Net is that you have the (paged) snapshot, and it is automatically managing locking and updating when you call another page. But that works only reliably with server-based cursors.
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