Re: Transactions ISOLATIONS level

> > 2) When I issue a SELECT FOR UPDATE the transaction level switches
> > automatically to TRANSACTIONS_SERIALIZABLE ?
Hi Fumi,
well this looks surprising a bit, (though I'm not a big expert of Oracle !) but I imagined that if you issue a SELECT for UPDATE on the WHOLE table then you lock enterely the table, so nobody else can for example insert or modify other records on the table 'til you issue a commit...so the isolation
level should be higher...I expect it to be TRANSACTION_SERIALIZABLE... please correct me if I'm wrong (as I said I have just a basic Oracle knowledge!)
Regards
Francesco

"fumi" <fumi_at_tpts5.seed.net.tw> ha scritto nel messaggio news:9hfkhm$f68$8_at_news.seed.net.tw...
>
> "Francesco Marchioni" <fmarchioni_at_libero.it> ¼¶¼g©ó¶l¥ó
> news:jSl_6.5944$363.259102_at_news.infostrada.it...
> > Hi all,
> > I'm studying transactions isolation levels.
> > I have some questions, hope somebody will help me:
> >
> > 1) How can I change the transaction isolation level via SQL - PL/SQL ?
> > ( I mean without administrator's tools)
>
>
> Oracle supports only SERIALIZABLE and READ COMMITTED.
> Use the SQL command:
>
> ALTER SESSION SET ISOLATION_LEVEL= {SERIALIZABLE | READ COMMITTED}
>
> By the way, I think no tools support this rare used statement.
>
> > 2) When I issue a SELECT FOR UPDATE the transaction level switches
> > automatically to TRANSACTIONS_SERIALIZABLE ?
>
>
> No, after you issue a SELECT FOR UPDATE command,
> you still in (default) READ COMMITTED level.
>
> > 3) I understand row locking and table locking but what does it mean
 "page"
> > locking ??
>
>
> Oracle doesn't use page lock.
> Page lock means that if you locks one or more rows in a page (block),
> then all rows in the page (block) are locked.
>
>
>
Received on Fri Jun 29 2001 - 16:30:34 CDT