what's the effect of NOHOLDLOCK in a SELECT query

I think NOHOLDLOCK isn't equal to NOLOCK.
So,will NOHOLDLOCK lead to dirty read?
if NOHOLDLOCK lead to dirty read,then how to distinguish
between NOHOLDLOCK and at isolation READ UNCOMMITTED?
1
gaoogle
7/6/2006 8:48:38 AM
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NOHOLDLOCK - NOLOCK = HOLD

The difference between these is the NOHOLDLOCK is typically used on SELECT
statements involved in "isolation level 3" transactions where the shared lock on
the data is released immediately after reading the data (ie, simulate isolation
level 1, while using isolation level 3).  It has nothing to do with dirty reads.

There is no such thing as NOLOCK in ASE.  Dirty reads are implemented using "at
isolation read uncommitted", or "set transaction isolation level 0".

Note:

select *
from mytable NOLOCK
where col1 = "xxxx" ....

simply assigns the alias "NOLOCK" to the table.  Doesn't change the locking
mechanism at all.

<gaoogle@gmail.com> wrote in message news:44acce66.3313.1681692777@sybase.com...
> I think NOHOLDLOCK isn't equal to NOLOCK.
> So,will NOHOLDLOCK lead to dirty read?
> if NOHOLDLOCK lead to dirty read,then how to distinguish
> between NOHOLDLOCK and at isolation READ UNCOMMITTED?


0
Sherlock
7/6/2006 3:53:04 PM
Thanks!
But...,that is to say NOHOLDLOCK has no effect at isolation
level below 3?

> NOHOLDLOCK - NOLOCK = HOLD
>
> The difference between these is the NOHOLDLOCK is
> typically used on SELECT statements involved in "isolation
> level 3" transactions where the shared lock on the data is
> released immediately after reading the data (ie, simulate
> isolation level 1, while using isolation level 3).  It has
> nothing to do with dirty reads.
>
> There is no such thing as NOLOCK in ASE.  Dirty reads are
> implemented using "at isolation read uncommitted", or "set
> transaction isolation level 0".
>
> Note:
>
> select *
> from mytable NOLOCK
> where col1 = "xxxx" ....
>
> simply assigns the alias "NOLOCK" to the table.  Doesn't
> change the locking mechanism at all.
>
> <gaoogle@gmail.com> wrote in message
> > news:44acce66.3313.1681692777@sybase.com... I think
> > NOHOLDLOCK isn't equal to NOLOCK. So,will NOHOLDLOCK
> > lead to dirty read? if NOHOLDLOCK lead to dirty read
> > ,then how to distinguish between NOHOLDLOCK and at
> isolation READ UNCOMMITTED?
>
>
0
Gaogle
7/7/2006 1:05:59 AM
It also has this effect for isolation level 2 on APL tables, since this is
handled as level 3 ('real' level 2 is supported only for DOL tables).

Rob V.

<Gaogle> wrote in message news:44adb377.3dab.1681692777@sybase.com...
> Thanks!
> But...,that is to say NOHOLDLOCK has no effect at isolation
> level below 3?
>
> > NOHOLDLOCK - NOLOCK = HOLD
> >
> > The difference between these is the NOHOLDLOCK is
> > typically used on SELECT statements involved in "isolation
> > level 3" transactions where the shared lock on the data is
> > released immediately after reading the data (ie, simulate
> > isolation level 1, while using isolation level 3).  It has
> > nothing to do with dirty reads.
> >
> > There is no such thing as NOLOCK in ASE.  Dirty reads are
> > implemented using "at isolation read uncommitted", or "set
> > transaction isolation level 0".
> >
> > Note:
> >
> > select *
> > from mytable NOLOCK
> > where col1 = "xxxx" ....
> >
> > simply assigns the alias "NOLOCK" to the table.  Doesn't
> > change the locking mechanism at all.
> >
> > <gaoogle@gmail.com> wrote in message
> > > news:44acce66.3313.1681692777@sybase.com... I think
> > > NOHOLDLOCK isn't equal to NOLOCK. So,will NOHOLDLOCK
> > > lead to dirty read? if NOHOLDLOCK lead to dirty read
> > > ,then how to distinguish between NOHOLDLOCK and at
> > isolation READ UNCOMMITTED?
> >
> >


0
Rob
7/7/2006 8:27:38 AM
Reply:

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