Re: read consistency

Michel Cadot wrote:
> "Prasath" <prasath.rao_at_gmail.com> a écrit dans le message de news: 1151596534.551557.236640_at_x69g2000cwx.googlegroups.com...
> | 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.

>From Ch 1.>>

Read consistency, as supported by Oracle, does the following:

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 -- Received on Thu Jun 29 2006 - 14:51:39 CDT