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Mutex table howto

Posted on 2001-06-21
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Last Modified: 2008-03-10
Hi all,

How do i create a mutex table in a database and ensure consistency using standard SQL.

Scenario:

Multiple clients must be able to perform the following sequence:

set mutex
read value from table
process value
update value in table
release mutex

Unique client id's are not available.

Preferable only the statements select, update, insert and delete is used. The solution must work with at least oracle and mySQL.

Regards
/S?ren




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Question by:svanggaard
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Expert Comment

by:Brendt Hess
ID: 6215755
Try using the FOR UPDATE option on your SELECT statement, e.g.:

SELECT * From MyTable WHERE ID = 1 FOR UPDATE

This locks the rows, disallowing updates from other processes until they are released.

Both MySQL and Oracle support this syntax.
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Author Comment

by:svanggaard
ID: 6217922
The SELECT FOR UPDATE is not supported by mySQL.

mySQL only supports locking an entire table.

Regards

/S?ren
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LVL 32

Expert Comment

by:Brendt Hess
ID: 6218992
Hmmm... according to the documentation at MySQL.Com, this is supported...

"If you are using FOR UPDATE on a table handler with page/row locks, the examined rows will be write locked. "

Researching more, this means that you will need the InnoDB version of MySQL.  If you cannot use this for some reason, then you are right - you will need an external Mutex handler of some sort.

See:  http://www.mysql.com/doc/I/n/InnoDB.html
for more info on InnoDB tables and their use.

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by:nico5038
ID: 7257289

No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:
 - PAQ'd and pts removed
Please leave any comments here within the
next seven days.

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER !

Nic;o)
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Accepted Solution

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Jgould earned 0 total points
ID: 7282238
Question has been closed as per recommendation

JGould-EE Moderator
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