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From: Laurenz Albe <[email protected]>
To: Bruce Momjian <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: correction
Date: Fri, 13 May 2022 23:49:09 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>

On Fri, 2022-05-13 at 16:36 -0400, Bruce Momjian wrote:
> On Wed, May 11, 2022 at 12:36:11PM +0200, Laurenz Albe wrote:
> > On Wed, 2022-05-11 at 00:33 +0000, PG Doc comments form wrote:
> > > The following documentation comment has been logged on the website:
> > > 
> > > Page: https://www.postgresql.org/docs/14/transaction-iso.html
> > > Description:
> > > 
> > > in this page: https://www.postgresql.org/docs/14/transaction-iso.html
> > > 
> > > under the Table 13.1 section, if we search for "phantom reads. Stricter
> > > behavior is permitted by the SQL standard", do we mean "Looser behaviour"?
> > 
> > What is meant is "The SQL standard allows an implementation to implement
> > stricter behavior than required by the standard; it only defines the things
> > that are *not* allowed to happen at a certain isolation level.  So it is for
> > example fine for PostgreSQL not to allow dirty reads in READ UNCOMMITTED
> > isolation level."
> > 
> > Perhaps this could be rewritten to be clearer; it is indeed easy to
> > misunderstand that sentence.
> 
> How is this attached patch's wording?
> 
> diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
> index 341fea524a..244694b07f 100644
> --- a/doc/src/sgml/mvcc.sgml
> +++ b/doc/src/sgml/mvcc.sgml
> @@ -277,8 +277,8 @@
> 
>     <para>
>      The table also shows that PostgreSQL's Repeatable Read implementation
> -    does not allow phantom reads.  Stricter behavior is permitted by the
> -    SQL standard: the four isolation levels only define which phenomena
> +    does not allow phantom reads.  The SQL standard allows more restrictive
> +    behavior:  the four isolation levels only define which phenomena
>      must not happen, not which phenomena <emphasis>must</emphasis> happen.
>      The behavior of the available isolation levels is detailed in the
>      following subsections.

I think that suffers from the same problem: izt sounds like the standard allows
stricter behavior than PostgreSQL.

How about:

  The table also shows that PostgreSQL's Repeatable Read implementation
  does not allow phantom reads.  That is fine, because the SQL standard only
  specifies which anomalies must <emphasis>not</enphasis> occur at a certain
  isolation level.  It is no problem if an implementation provides higher
  guarantees than required.
  The behavior of the available isolation levels is detailed in the
  following subsections.

Yours,
Laurenz Albe

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