RE: lock collisions

Fri, 19 Mar 2004 06:32:06 -0800

Thanks by your help.

Jos� R�mulo El�as Contreras
Ingeniero en Sistemas Computacionales
Guadalajara, Jalisco
Tel: (33) 3126-47-81 y 3126-48-13
Cel: (311) 910-50-59




From: "Zabach, Elke" <[EMAIL PROTECTED]>
To: 'Jos� R�mulo El�as Contreras' <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
Subject: RE: lock collisions
Date: Fri, 19 Mar 2004 11:49:22 +0100

Jos� R�mulo El�as Contreras wrote:

>
> Hi:
>
>       In a connection with isolation level 0, I put an
> exclusive lock to a
> row. Another connection with the same isolation level can
> read this row if
> the transacion of the first connection is not finished?

It is the definition of isolation level 0 (read uncommitted) to be able
to READ data no matter if it is committed/rollbacked/locked/not locked.
--> yes, reader with isolevel 0 can read it.

>
>       What are the posibles collisions that can happen in
> connections with
> isolation level 0, if in the update staments I put an
> exclusive lock for
> each row that will be update?

The others with isolevel 0 will not be able to update/delete
this row, to SELECT..FOR UPDATE when this row would be selected,
will not be able to lock (no matter if share or exclusive) the specific
row or the whole table and will not be able to change the table definition
for the specific table with some DDL (ALTER TABLE for example, CREATE INDEX).

Elke
SAP Labs Berlin

>
> Thanks
>
> Jos� R�mulo El�as Contreras
> Ingeniero en Sistemas Computacionales
> Guadalajara, Jalisco
> Tel: (33) 3126-47-81 y 3126-48-13
> Cel: (311) 910-50-59
>
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