Isolation Level 비교

@ipajama 2011. 6. 12. 21:37

2011. 6. 12. 21:37

Oracle Database Isolation Levels

Isolation Level Description

Isolation Level	Description
Read committed (default)	This is the default transaction isolation level. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. An Oracle Database query never reads dirty (uncommitted) data. Because Oracle Database does not prevent other transactions from modifying the data read by a query, that data can be changed by other transactions between two executions of the query. Thus, a transaction that runs a given query twice can experience both nonrepeatable read and phantoms.
Serializable	Serializable transactions see only those changes that were committed at the time the transaction began, plus those changes made by the transaction itself through `INSERT`, `UPDATE`, and `DELETE` statements. Serializable transactions do not experience nonrepeatable reads or phantoms.
Read-only	Read-only transactions see only those changes that were committed at the time the transaction began and do not allow `INSERT`, `UPDATE`, and `DELETE` statements.

Read committed (default)

This is the default transaction isolation level. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. An Oracle Database query never reads dirty (uncommitted) data.

Because Oracle Database does not prevent other transactions from modifying the data read by a query, that data can be changed by other transactions between two executions of the query. Thus, a transaction that runs a given query twice can experience both nonrepeatable read and phantoms.

Serializable

Serializable transactions see only those changes that were committed at the time the transaction began, plus those changes made by the transaction itself through INSERT, UPDATE, and DELETE statements. Serializable transactions do not experience nonrepeatable reads or phantoms.

Read-only

Read-only transactions see only those changes that were committed at the time the transaction began and do not allow INSERT, UPDATE, and DELETE statements.

DB2 Isolation Levels

ANSI SQL Isolation Level	DB2 UDB equivalent
SERIALIZABLE	Repeatable read (RR)
REPEATABLE READ	Read stability (RS)
READ COMMITTED (default)	Cursor stability (CS) Currently Committed (CC)
READ UNCOMMITTED	Uncommitted read (UR)



Informix Isolation Levels
SET TRANSACTION correlates with SET ISOLATION Read Uncommitted (nologging default) Dirty Read Read Committed (logging default) Committed Read Not Supported Cursor Stability (ANSI) Repeatable Read Serializable (IBM Informix) Repeatable Read (IBM Informix) Repeatable Read Oracle http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/consist.htm#BABIJEJI http://blog.naver.com/PostView.nhn?blogId=joonaha&logNo=70105748469&viewDate=¤tPage=1&listtype=0 http://e-jooyoung.net/tc/76?TSSESSIONejooyoungnettc=17b13c012d47fb0d3f66e5d4755bdbc4 DB2 http://publib.boulder.ibm.com/infocenter/iwedhelp/v6r0/index.jsp?topic=%2Fcom.ibm.db2e.doc%2Fdb2e_iso_levels.html http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/index.jsp?topic=/com.ibm.db2.luw.wn.doc/doc/i0056249.html Informix http://www.database.sarang.net/?inc=read&aid=571&criteria=informix&subcrit=&id=947&limit=20&keyword=&page=70 http://publib.boulder.ibm.com/infocenter/idshelp/v10/index.jsp?topic=/com.ibm.sqlt.doc/sqltmst239.htm http://publib.boulder.ibm.com/infocenter/idshelp/v115/index.jsp?topic=/com.ibm.sqlt.doc/ids_sqt_389.htm

SET TRANSACTION correlates with	SET ISOLATION
Read Uncommitted (nologging default)	Dirty Read
Read Committed (logging default)	Committed Read
Not Supported	Cursor Stability
(ANSI) Repeatable Read Serializable	(IBM Informix) Repeatable Read (IBM Informix) Repeatable Read

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