Re: oracle - mysql comparison

From: Daniel Morgan <damorgan_at_x.washington.edu>
Date: Fri, 16 Jul 2004 18:20:27 -0700
Message-ID: <1090027247.885352@yasure>

VC wrote:

> Hello Daniel,
>
> "Daniel Morgan" <damorgan_at_x.washington.edu> wrote in message
> news:1089945278.134355_at_yasure...
>

>>VC wrote:
>>
>>
>>>A correct concurrency control/model ensures that all the permitted
>>>transactions are serializable.  In this sense, databases like DB2 or

>
> MSSQL
>

>>>implement a correct concurrency model albeit at the expense of lower
>>>concurrency in some circumstances.  Funnily enough,  none of  the Oracle
>>>isolation levels can make the same promise, i.e. ensure serializable
>>>transaction histories, in any of its isolation levels.  Usually,  it's

>
> quite
>

>>>easy to obtain correct results by augmenting an isolation level with
>>>something like 'select for update',  though..
>>
>>And if this is true why, exactly, would anyone care at the expense of
>>being able to extract an accurate answer from a database without
>>performing table locks on all resources?
>>

>
>
> I am not sure what specific part of my message the word *this* ('if this is
> true') refers to, but assuming it's the last sentence then you surely know
> that 'select for update' takes write (TX) lock on all the rows involed A
> locking scheduler would take *read* row level locks in similar circumstances
> automatically. If my interpretaion is incorrect, please elaborate.
>
> VC

My point is that in all of the other databases to which you have referred it is impossible to get a result set consistent to a point-in-time without locking the resources (not at the row level but at the table level).

Something I would think far more important than anything you brought up.

In Oracle this can be achieved without any locking.

Daniel Morgan Received on Fri Jul 16 2004 - 20:20:27 CDT