Re: read consistency
- From: "Mark D Powell" <Mark.Powell@xxxxxxx>
- Date: 29 Jun 2006 12:51:39 -0700
Michel Cadot wrote:
"Prasath" <prasath.rao@xxxxxxxxx> a écrit dans le message de news: 1151596534.551557.236640@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| Session 1:
| --------------------
| select * from my_table; ->takes 5 minutes
|
| Session 2:
| -------------------
| delete from my_table where my_col = 1; -> takes less than 1 second
|
| commit;
|
|
| Question
| ---------------------
| Do the records deleted in session 2 appear in session 1?
|
Yes, if session 1 query starts before session 2 commit.
Regards
Michel Cadot
Definitely as Michel said. By default all SQL statements are read
consistent at the point in time of when the statement starts execution.
The Oracle read consistency model is discussed in the Concepts Manual
for your version. For 9.2 the chapter is 20 Data Concurrency and
Consistency.
Read consistency, as supported by Oracle, does the following:From Ch 1.>>
Guarantees that the set of data seen by a statement is consistent with
respect to a single point in time and does not change during statement
execution (statement-level read consistency)
Ensures that readers of database data do not wait for writers or other
readers of the same data
Ensures that writers of database data do not wait for readers of the
same data
Ensures that writers only wait for other writers if they attempt to
update identical rows in concurrent transactions
<<
HTH -- Mark D Powell --
.
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- From: Michel Cadot
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