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Table locking with nested sets?

Posted on 2008-10-09
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Last Modified: 2012-08-14
I'm attempting to use nested sets to represent a data hierarchy (see: http://dev.mysql.com/tech-resources/articles/hierarchical-data.html, except I'm doing it in SQL 2000, not MySQL).

I've written a stored procedure that handles an insert, it looks something like this the simplified code snippet I've attached.  It works fine, but my concern is about concurrent users (i.e. someone else updating/inserting and affecting the hierarchy at the same time).  The MySQL example uses a lock on the what I can only assume is the whole table before doing anything, but this seems like it might be
dangerous and/or overkill, especially if this data is ultimately being viewed a lot on a public web site.  I thought about just creating a seperate table with one field and one row to act as a lock in this stored procedure (and potentially a couple other related SPs), but that doesn't seem like a best practice.

Any thoughts?

CREATE PROCEDURE [dbo].[INSERT_NESTED_SET_WEBPAGE]
	@varTitle varchar(256),
	@parent int
AS
 
-- get the parent's rgt value
DECLARE @parentRight int;
SELECT @parentRight = rgt FROM my_data WHERE ID = @parent
 
-- make room for the new child (at the end of the nested set)
UPDATE my_data SET lft = lft + 2 WHERE lft >= @parentRight
UPDATE my_data SET rgt = rgt + 2 WHERE rgt >= @parentRight
 
-- insert the new child (at the end of the nested set)
INSERT INTO my_date (title, lft, rgt) VALUES (
	@varTitle,
	@parentRight,
	@parentRight + 1)
 
GO

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Question by:saitwebdev
2 Comments
 
LVL 14

Accepted Solution

by:
puranik_p earned 250 total points
ID: 23054534
Just put the whole thing in a transaction. That's it!
The transactions are the simplest way to take care of the concurrency.
CREATE PROCEDURE [dbo].[INSERT_NESTED_SET_WEBPAGE]
        @varTitle varchar(256),
        @parent int
AS
 
-- get the parent's rgt value
DECLARE @parentRight int;
BEGIN TRANSACTION
SELECT @parentRight = rgt FROM my_data WHERE ID = @parent
 
-- make room for the new child (at the end of the nested set)
UPDATE my_data SET lft = lft + 2 WHERE lft >= @parentRight
UPDATE my_data SET rgt = rgt + 2 WHERE rgt >= @parentRight
 
-- insert the new child (at the end of the nested set)
INSERT INTO my_date (title, lft, rgt) VALUES (
        @varTitle,
        @parentRight,
        @parentRight + 1)
 
COMMIT TRANSACTION
GO

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Author Closing Comment

by:saitwebdev
ID: 31504784
Thank you.  I came to that conclusion some time ago, but it's good to have confirmation.
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