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From:Anupam Karmarkar Date:January 17 2014 1:15pm
Subject:Index locking Query
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Hi All,

I have situation here about Innodb locking.
In  transaction, We select from XYZ transaction table values and then updates it
like below

SESSION 1:

START TRANSACTION;
SELECT ID INTO vID FROM XYZ WHERE FLAG = 1 ORDER BY TIME LIMIT 1 FOR UPDATE;
UPDATE XYZ SET FLAG=0 WHERE ID = vID;
COMMIT;

SESSION 2:

UPDATE XYZ SET FLAG=1 WHERE ID = 2;


We are keep on getting deadlock due to index locking, there is index on FLAG, we can
allow phantom read in session 1, we tried with READ COMMITTED but still same, I think
issue with next-key locking.

If i do following in SESSION 1 would that help in locking or still it would lock index.
Any suggestion.

SESSION 1:

START TRANSACTION;
UPDATE XYZ SET FLAG=0,ID=(@oID:=ID) ORDER BY TIME LIMIT 1;

SELECT @oID AS ID;
COMMIT;
Thread
Index locking QueryAnupam Karmarkar17 Jan 2014