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> Serializable distributed transactions
curiousjoe
post Mar 27 2012, 03:16 PM
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Hello,

here http://www.dba-oracle.com/t_oracle_isolation_level.htm
you wrote that

"The serializable transaction isolation level is not supported with distributed transactions."

Can you please elaborate what is not supported (or example on what is not working properly)? I falied to find confirmation on this in Oracle documentation...

thanks
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burleson
post Mar 27 2012, 03:26 PM
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Hi Joe,


>> Can you please elaborate what is not supported

The idea is to prevent dirty reads. As I understand it, it's possible in a distributed transaction to get a non-repeatable read bnecause the read consistency does not work across databases.

In the serializable transaction isolation level non-repeatable and phantom reads are not possible.

From the docs, read about "in question" transactions:

http://docs.oracle.com/cd/B10501_01/server...521/ds_txns.htm


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Hope this helps. . .

Donald K. Burleson
Oracle Press author
Author of Oracle Tuning: The Definitive Reference
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aussie_dba
post Mar 28 2012, 02:39 AM
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http://docs.oracle.com/cd/B10501_01/server...txnman.htm#9511

QUOTE
An important restriction exists in Oracle's implementation of distributed read consistency. The problem arises because each system has its own SCN, which you can view as the database's internal timestamp. The Oracle database server uses the SCN to decide which version of data is returned from a query.
. . .
One consequence of the SCN gap is that two consecutive SELECT statements can retrieve different data even though no DML has been executed between the two statements.
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