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HOW IS TRANSACTION ISOLATION LEVEL SET  VS SESSION.tx_isolation?

Posted on 2014-02-25
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Last Modified: 2014-11-03
This is a basic question or so I believe!

Where and how do you set a current transaction isolation setting
I checked @@session.tx_isoation an @@tx_isolation are the same

so what variable or sql command sequence  sets things such that it is either transaction specific to a specific transaction or the default for just begin end transactions???

there is supposed to be three different setting but I found only 2 so far: session and global
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Question by:Robert Silver
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11 Comments
 
LVL 23

Expert Comment

by:Steve Wales
ID: 39886313
(oops, ignore me, I gave you MSSQL advice, removing my comment, sorry about that)

However, in case you hadn't found it, since I've got a comment stuck here anyway, here's the link to the docs on isolation level for MySQL.

http://dev.mysql.com/doc/refman/5.0/en/set-transaction.html
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LVL 2

Author Comment

by:Robert Silver
ID: 39887079
I know not much help I need specifics not given at your link
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LVL 23

Expert Comment

by:Steve Wales
ID: 39887119
Sorry can't help you ... I don't know much about MySQL, mis-read it as MSSQL and replied based on that :-/
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LVL 2

Author Comment

by:Robert Silver
ID: 39931707
This question may not have an easy answer or even be so relevant.
I had heard  of this setting and wish to know how it is set that is all
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LVL 2

Author Comment

by:Robert Silver
ID: 39931711
Perhaps the real answer here is the session becomes specific to a given Transaction given
it is within the same session but then why make the distinction?
Was that just a mistake that was made and there is no such setting at all?
That would be my current  thoughts on this?
With Multi-threading it just occurred to me that maybe I could set off one transaction or multiple transactions within the same session but I guess that is not possible given the response here

Anyone like to comment on that?
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LVL 51

Expert Comment

by:Mark Wills
ID: 40365773
If I understand your question properly... You are correct, there are three.

The basic syntax is :
mysql> SET <extent> TRANSACTION ISOLATION LEVEL <level>;

You must specify the extent as being GLOBAL or SESSION and if neither keyword is mentioned, then it is for the next (unstarted) transaction only.

There are 4 levels (in sequence of increasing guaranteed integrity) :
READ UNCOMMITTED
READ COMMITTED
REPEATABLE READ
SERIALIZABLE

The  REPEATABLE READ level is the default...
0
 
LVL 51

Accepted Solution

by:
Mark Wills earned 2000 total points
ID: 40365823
Found an example for you at the transaction level and the results / outcomes between two sessions...

http://dba.fyicenter.com/faq/mysql/Change-Transaction-Isolation-Level.html
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LVL 2

Author Comment

by:Robert Silver
ID: 40417809
I've requested that this question be deleted for the following reason:

No interest
0
 
LVL 51

Expert Comment

by:Mark Wills
ID: 40417810
Interesting to say "no interest"

There was an example given of how to set and test for current transaction, and previously, the three different methods used to set the isolation level... being Global or Session and if neither of those two keywords are mentioned, then it is Transaction.
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LVL 2

Author Comment

by:Robert Silver
ID: 40419543
I've requested that this question be deleted for the following reason:

No decent answer or interest
0

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