Re: how to build a database from scratch
Date: 9 Dec 2006 01:21:10 -0800
Message-ID: <1165656070.480073.257140_at_f1g2000cwa.googlegroups.com>
NENASHI, Tegiri a écrit :
> "Cimode" <cimode_at_hotmail.com> wrote in
> > SQL and DB2 have been implementing ORACLE Read Consistency since the
> > SQL2005 and UDB 8.2.
>
> Is it that before 2005 SQLServer could not be used ? Or DB2 before 8.2 ?
> It was speculated that "you can't use it unless you know precisely what
> data is going to be touched".
More information to be more explicit...
B4 SQL2005 or DB2 8.2 by default, exclusive locks were put on objects
in the process of being updated until the change was commited. As a
consequence, during the transaction the object could not be selected
and user had to wait until the transaction was commited to get a
result.
> The deadlocks. SQL Server 2005 with Snapshot, that I think is the same
> like Read consistency of Oracle, can still have deadlocks because it uses
> locks when one upates rows.
Some caution here on terminology...Locks and deadlocks are not the
same...Locks are physical pointers indicating which part of data are
not candidate to be changed in a specific point in time...They are a
part of a *normal* mechanism to handle concurrency in SQL DBMS's.
Deadlocks, OTOH refer to an exceptional situation where two processes
are waiting for one another to release a lock on a specific object.
Received on Sat Dec 09 2006 - 10:21:10 CET