Re: Locklevel

Hi Dirk,

Depending on what you're doing, Oracle has different default levels of locking that they can be summarised into two groups:

Row Level Locks
Table Level Locks

In your select for update example, Oracle locks all selected rows exclusively and locks the table in what is known as a Row Share Table Lock (RS or SS). The table lock prevents certain other table locks from being held.

Oracle has no concept of a page or block level locks so row level locks can never escalate up to block levels locks.

The golden rule with Oracle default locking behaviour is that readers never block writers and writers never block readers.

My big recommendation would be for you to read the Data Concurrency and Consistency section of the Concepts manual where all is explained.

Cheers

Richard

"Dirk Scheer" <dirk.scheer_at_stadt-mh.de> wrote in message news:akfq4b$svr$1_at_rzcom2.stadt-mh.de...
> Hello out there,
>
> can anybody tell me, what the default lock level of an Oracle database is?
> If I do a
>
> select ... from ... for update;
>
> Are there only the records found locked?
> Is it possible to lock a complete block?
>
> If it sounds a little bit strange to you: I'm coming from Informix. This
> database distinguishes between row level and page level locking. Are there
> comparable mechanism in Oracle?
>
> Thx in advance...
> Dirk
> --
> Stadt Mülheim an der Ruhr
> Amt 10-3
> Telefon: (0208) 455-1006 Fax: (0208) 455-58-1006
> http://www.muelheim-ruhr.de/
Received on Tue Aug 27 2002 - 07:50:29 CDT