Re: Locks Oracle v SQL7

In article <1kP75.1291$xf5.9234_at_news2.atl>,   "Michael D. Long" <lead_dog_at_bellsouth.net> wrote:
>
> When posting a question such as yours it would be best
> to qualify whether local or distributed transactions are
> being employed. Locking behavior changes somewhat
> based on the isolation level. As distributed transactions
> run at 'READ SERIALIZABLE', the characteristics will be
> significantly different than 'READ COMMITTED'.
>

no they don't. the default isolation is read committed be it distributed or single site. In both cases you must set isolation_level=serializable if thats what you want, else its read committed.

The locking characteristics at serializable is the same actually as read committed so that wouldn't matter too much either.

o non-blocking reads (consistent reads). writes don't block reads,   reads don't block writes.

o no read locks taken out for selects.

o exclusive locks (that do not prevent reads) for modifications only.

> --
> Michael D. Long
> http://extremedna.homestead.com
>
> "Jack" <No_at_Mail.Please> wrote in message
> news:gCZ65.5733$uO1.42486_at_news1-hme0...
> > How does Oracle compare with Sql7 as regards Locking problems.
> >
> > For instance, does Oracle put locks on Select statements, what
 Locks does
 it
> > put on Update and Insert statements?
> >
> > Sql7 puts 'read only' Shared locks on all the above statements
 (default
> > Isolation mode) but converts the Update and Insert statements (after
> > satisfying the Insert and Update conditions) into Exclusive locks
 in order
> > to do the actual Insert and Update operations. This 'conversion'
 often
> > causes deadlocks.
> >
> > How about Oracle does it have 'Lock' problems?
> >
> > Thanks
> > J
> >
> >
>
>

--
Thomas Kyte (tkyte_at_us.oracle.com) Oracle Service Industries
Howtos and such: http://osi.oracle.com/~tkyte/index.html
Oracle Magazine: http://www.oracle.com/oramag
Opinions are mine and do not necessarily reflect those of Oracle Corp


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