Re: ADO.NET 2.0 - Question for Microsoft Employees

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Fantastic answer Pablo and this clarifies a lot.

I have another quick question.

If I want to use read-commited-snapshot in SQL2k5, through ADO.NET, do I use

ReadCommitted
or do I use
ReadCommited | Snapshot

Strange the binary values are such that they can be or'ed. So I was curious
:)

- Sahil Malik [MVP]
http://codebetter.com/blogs/sahil.malik/



"Pablo Castro [MS]" <pablocas@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:uWC5h6fOFHA.2604@xxxxxxxxxxxxxxxxxxxxxxx
> Most of the information is this thread is right, let me just try to
organize
> it a little bit.
>
> IsolationLevel.Snapshot was introduced to be used in databases that
> distinguish multiversioning-based serializable isolation from
locking-based
> serializable isolation (ok, that's SQL Server :)
>
> Both protect applications from the same phenomena, but in different ways
and
> there are some semantic implications to it (e.g. contention versus
> optimistic locking)
>
> In SQL Server you can also enable "read-committed-snapshot" to get
> snapshot-based read committed isolation level. Since that's a
database-level
> option, you can just use IsolationLevel.ReadCommitted.
>
> In Oracle, isolation is implemented through versioning so existing
> isolation-levels already implied versioning-like semantics, through
> different phenomena would show up or not depending on which of the two
> supported isolation levels is picked.
>
> As for snapshot isolations being for reads, that's not strictly accurate.
> Snapshot isolation helps reduce contention, and as a trade-off you have
more
> overhead on reads and writes (this can vary *a lot* depending on the
> workload, so don't take this as a general guidance). Contention reduction
> means, for example, that even if you have long-running read operations
(e.g.
> long-running SELECTs for reporting) you can still do updates without
> waiting. Same the other way around: if you have long-running operations
that
> changed rows, your SELECTs don't need to wait until that operation
finishes
> before reading values.
>
> --
> Pablo Castro
> Program Manager - ADO.NET Team
> Microsoft Corp.
>
> This posting is provided "AS IS" with no warranties, and confers no
rights.
>
>
> "Sahil Malik" <contactmethrumyblog@xxxxxxxxxx> wrote in message
> news:O3caPnSOFHA.2132@xxxxxxxxxxxxxxxxxxxxxxx
> > Hey atleast that is what OracleClient MSDN says. I decompiled ODP.NET
(10)
> > using reflector and suspicions confirmed there too.
> >
> > As I am writing the book, I am giving attention to Oracle wherever it
> > warrants it. In besides updation and transactions - there isn't much
else.
> >
> > - Sahil Malik
> > http://codebetter.com/blogs/sahil.malik/
> >
> >
> >
> >
> > "Frans Bouma [C# MVP]" <perseus.usenetNOSPAM@xxxxxxxxx> wrote in message
> > news:#fIq9VSOFHA.3808@xxxxxxxxxxxxxxxxxxxxxxx
> >> Sahil Malik [MVP] wrote:
> >> > Frans,
> >> >
> >> > Yeah thats true, but snapshot is more for reads .. isn't it? I mean,
> >> > how
> >> > does it apply to writes? Writes in oracle are either Readcommitted or
> >> > Serializable.
> >>
> >> As I understand it, normally, a writer in Oracle writes to its own
> >> version, so a reader won't see the change until the transaction is
> >> committed.
> >>
> >> > I believe IsolationLevel.Snapshot is not supported in .NET 2.0
> >> > OracleClient - which seemed hella odd, so I thought I'd post a
message
> > here
> >> > and find out for sure if it is going to be supported at all.
> >>
> >> In that case it's pretty odd indeed, as it should be the normal
> >> behavior. But I have to look up the details as well, and Oracle docs
are
> >> erm... massive :)
> >>
> >> FB
> >>
> >> >
> >> > The default IMO is ReadCommitted for both SQL Server & Oracle.
> >> >
> >> > - Sahil Malik [MVP]
> >> > http://codebetter.com/blogs/sahil.malik/
> >> >
> >> >
> >> >
> >> >
> >> > "Frans Bouma [C# MVP]" <perseus.usenetNOSPAM@xxxxxxxxx> wrote in
> >> > message
> >> > news:eOZQ4BPOFHA.604@xxxxxxxxxxxxxxxxxxxxxxx
> >> >
> >> >>Sahil Malik wrote:
> >> >>
> >> >>>Okay, so we have a new Isolationlevel for transactions in ADO.NET -
> >> >>>the
> >> >>>snapshot isolation.
> >> >>>
> >> >>>That exists at System.Data - which leads me to believe that nothing
> >> >>>really stops me from setting that isolation level on Oracle.
> >> >>>
> >> >>>So my question is - by setting that on Oracle, does it mean the same
> >> >>>as
> >> >>>
> >> >>>SET TRANSACTION READ ONLY
> >> >>>
> >> >>>Or does Isolationlevel.Snapshot not work on Oracle?
> >> >>>
> >> >>>(Frankly my opinion, IsolationLevel.Snapshot not working on Oracle
is
> > not
> >> >>>a good answer, but if that is what it does, then that is what it
does
> > ..)
> >> >>>
> >> >>>Can anyone advise? :)
> >> >>
> >> >>Snapshot IS oracle :D. Databases, during transactions, use various
> >> >>kinds
> >> >>of locking mechanisms to ensure consistency. They all work more or
less
> >> >>the same: depending on the transaction isolation level, other
> > transactions
> >> >>can read the data changed or have to wait till the exclusive lock is
> >> >>lifted from the row or table.
> >> >>
> >> >>Oracle uses a different strategy in that it uses a Snapshot isolation
> >> >>level, in which writers don't block readers in any way and readers
> > simply
> >> >>get an older version of the modified data, till the transaction has
> >> >>been
> >> >>completed. This locking mechanism was unique for oracle but is now
also
> >> >>implemented in Sqlserver. It works together with MVCC, which ensures
> >> >>multiple copies of the same data during different transactions.
> >> >>
> >> >>If I'm not mistaken snapshot is what oracle does by default, for
> >> >>example
> >> >>when you don't start a transaction explicitly, but I have to look
that
> > up.
> >> >>Basicly, snapshot is the isolation level which avoids deadlocks and
> >> >>also
> >> >>avoids dirty reads.
> >> >>
> >> >>FB
> >> >>
> >> >>--
> >>
>>------------------------------------------------------------------------
> >> >>Get LLBLGen Pro, productive O/R mapping for .NET:
> >> >>http://www.llblgen.com
> >> >>My .NET blog: http://weblogs.asp.net/fbouma
> >> >>Microsoft MVP (C#)
> >>
>>------------------------------------------------------------------------
> >> >
> >> >
> >> >
> >>
> >>
> >> --
>
>> ------------------------------------------------------------------------
> >> Get LLBLGen Pro, productive O/R mapping for .NET:
http://www.llblgen.com
> >> My .NET blog: http://weblogs.asp.net/fbouma
> >> Microsoft MVP (C#)
>
>> ------------------------------------------------------------------------
> >
> >
>
>


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