RE: Thoughts on implicit/auto COMMITs

Brent is a friend and an ex-coworker. He wanted to share the background of this customer’s scenario, in case it would help you with yours.

I let Brent know some folks were having...fun…with his take on autocommit.

Jeff

Heh heh heh, I can only imagine. The difference on optimistic vs pessimistic concurrency nailed it though - the default combo of optimistic & implicit transactions makes sense in Oracle, and the default of pessimistic and automatic transactions makes sense in SQL Server. It's when you change only one of those two settings that you're screwed.

The blog post stemmed from an app that had been written by SQL Server people, and then an Oracle guy came in and made a few changes. He switched to implicit transactions without understanding that everybody was doing single-line inserts/updates all over the place in code, not bothering to set transactions. He didn't understand the impact of what he was doing. (Not an Oracle jab by any means - the guy was well-meaning but just not prepared.)

We got called in because performance went straight into the toilet. Even worse, rollbacks were rolling back completely unrelated transactions, and nobody knew why, hahaha.

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com> Sent: Thursday, March 15, 2018 7:54 AM
To: andysayer_at_gmail.com; arian_at_stijf.com Cc: oracle-l_at_freelists.org
Subject: RE: Thoughts on implicit/auto COMMITs

The setting is called the read_committed_snapshot which is set to off by default. This means that readers are blocking writers. Some applications might even rely on this behavior.

After setting read_committed_snapshot to on SQL Server will start to behave like Oracle in this respect. Row versions will be stored in the tempdb in such case.

Nenad

HYPERLINK "https://urldefense.proofpoint.com/v2/url?u=http-3A__nenadnoveljic.com_blog_&d=DwMGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=N2hWu5HFsaIjmMkjQbnlokJ7uinNZMgPVk8rqPT9esM&m=N2jhkTXmnzLLf0vy6CeiJ1kcmV1PW1GK0w_vcN7wS4w&s=vVgM07ureLRUyGe1dgJVpTmqbIigwSzNrIypiwvOexw&e="http://nenadnoveljic.com/blog/

From: HYPERLINK "mailto:oracle-l-bounce_at_freelists.org"oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Andy Sayer Sent: Donnerstag, 15. März 2018 12:19
To: HYPERLINK "mailto:arian_at_stijf.com"arian_at_stijf.com Cc: HYPERLINK "mailto:oracle-l_at_freelists.org"oracle-l_at_freelists.org Subject: Re: Thoughts on implicit/auto COMMITs

In ye olde regions of SQL Server land, writers block readers. This has spawned many silly workarounds like

Commit constantly

If a transaction is open for more than a second it must be killed

I believe there is some setting in more recent versions to prevent this. The workarounds are so blindly followed as best practise that the greener grass is a mystery to some.

Obviously this just doesn’t apply in the sane land of Oracle, writers don’t block readers. 

Regards,

Andrew

On Thu, 15 Mar 2018 at 09:13, Arian Stijf <HYPERLINK "mailto:arian_at_stijf.com"arian_at_stijf.com> wrote:

Hi,

in my opinion this breaks the A(tomicity) of ACID. E.g. a transaction consisting of two dependent inserts (Parent/child), and the first insert is commited before the second, then the database crashes.

Regards,

Arian

On 14-Mar-18 16:57, Rich J wrote:
>
> Hey all,
>
> As a solo DBA responsible for a number of SQL Servers in addition to
> Oracle, I try to read up on both.  One of the (more respected) SQL
> Server team blogs had this entry:
>
> HYPERLINK "https://urldefense.proofpoint.com/v2/url?u=https-3A__www.brentozar.com_archive_2018_02_set-2Dimplicit-5Ftransactions-2Done-2Dhell-2Dbad-2Didea_&d=DwMGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=N2hWu5HFsaIjmMkjQbnlokJ7uinNZMgPVk8rqPT9esM&m=N2jhkTXmnzLLf0vy6CeiJ1kcmV1PW1GK0w_vcN7wS4w&s=PyZyN7Prv057c2HZgi0EyA2t1MeBzR9TL1RSIhYyAeo&e="https://www.brentozar.com/archive/2018/02/set-implicit_transactions-one-hell-bad-idea/
>
> ..where they advocate the default auto-commit because otherwise the
> row (or page, or table) is locked should someone forget to COMMIT.
>
> This seems like an extraordinarily bad idea for anything but ad-hoc or
> one-off DML (without getting into a sidebar on that particular
> practice), whether Oracle or SQL Server or whatever.
>
> Or is it just me and some old-fashioned narrow RDBMS thinking?
>
> Rich
>

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