Re: I think that the transaction tutorial document (3.4) should mention transaction isolation

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От David G. Johnston
Тема Re: I think that the transaction tutorial document (3.4) should mention transaction isolation
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Msg-id CAKFQuwZ2yZivzZBQZJrE4TtzSQb3Mqvec1WUrbgL2EHSEcfeDA@mail.gmail.com
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Ответ на Re: I think that the transaction tutorial document (3.4) should mention transaction isolation  (Bruce Momjian <bruce@momjian.us>)
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On Wed, Mar 29, 2023 at 12:56 PM Bruce Momjian <bruce@momjian.us> wrote:
On Thu, Mar  2, 2023 at 01:55:31PM +0000, PG Doc comments form wrote:

> I think that a notice saying that for absolute transaction isolation you
> should set the default transaction isolation to serializable, and be
> prepared to have transactions fail, and referring to the more details
> document, would help users prevent consistency bugs.

Well, the point is that the application is _not_ retrieving a value and
setting is +100, but rather having the SQL add 100, which is kind of the
point. 

I don't think a tutorial should get into more details than that.

I'm on the fence, but leaning toward agreeing in principle.  The following paragraph from that page does cover the dynamics reasonably well under the default configuration and the tutorial should assume the reader hasn't changed the default.

"""
So transactions must be all-or-nothing not only in terms of their permanent effect on the database, but also in terms of their visibility as they happen. The updates made so far by an open transaction are invisible to other transactions until the transaction completes, whereupon all the updates become visible simultaneously.
"""

That said, the tutorial lacks any forward reference to non-tutorial information for the reader that wants to expand their knowledge in this area.  A paragraph mentioning isolation levels, including stating the default that the tutorial was operating under, and where that and the other modes are defined/explained, should be added to the end of that page.

David J.

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