From: Andres Freund <andres@anarazel.de>
To: David Steele <david@pgmasters.net>
Cc: pgsql-committers@postgresql.org
Subject: Re: pgsql: Make WAL segment size configurable at initdb time.
Date: Fri, 9 Nov 2018 19:30:52 -0800
Message-ID: <20181110033052.xmmozibdapwvenkx@alap3.anarazel.de> (raw)
In-Reply-To: <f572c66f-1840-b789-04e2-b767f4765c3a@pgmasters.net>
References: <E1duXBW-0003QB-4d@gemulon.postgresql.org>
<68ea97d6-2ed9-f339-e57d-ab3a33caf3b1@pgmasters.net>
<20181005165447.zyzglieznybyi7wu@alap3.anarazel.de>
<fd0855d1-4bf5-65fc-9c0f-ff64af3061ab@pgmasters.net>
<f572c66f-1840-b789-04e2-b767f4765c3a@pgmasters.net>
On 2018-11-09 21:45:18 -0500, David Steele wrote:
> On 10/5/18 1:03 PM, David Steele wrote:
> > Hi Andres,
> >
> > On 10/5/18 5:54 PM, Andres Freund wrote:
> >> On 2018-09-20 11:48:08 -0400, David Steele wrote:
> >>
> >>> diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
> >>> index e1073ac6d3..3bfd172441 100644
> >>> --- a/doc/src/sgml/config.sgml
> >>> +++ b/doc/src/sgml/config.sgml
> >>> @@ -8440,10 +8440,8 @@ dynamic_library_path =
> >>> 'C:\tools\postgresql;H:\my_project\lib;$libdir'
> >>> </term>
> >>> <listitem>
> >>> <para>
> >>> - Reports the number of blocks (pages) in a WAL segment file.
> >>> - The total size of a WAL segment file in bytes is equal to
> >>> - <varname>wal_segment_size</varname> multiplied by
> >>> <varname>wal_block_size</varname>;
> >>> - by default this is 16MB. See <xref
> >>> linkend="wal-configuration"/> for
> >>> + Reports the size of write ahead log segments.
> >>> + The default value is 16MB. See <xref
> >>> linkend="wal-configuration"/> for
> >>> more information.
> >>> </para>
> >>> </listitem>
> >>
> >> Why is this actually more correct? You mean because we have a conversion
> >> that does the mb conversion at display time?
> >
> > In pre-11 versions of Postgres, you get this:
> >
> > postgres=# select setting, unit from pg_settings where name =
> > 'wal_segment_size';
> > setting | unit
> > ---------+------
> > 2048 | 8kB
> >
> > But in v11 you get this:
> >
> > select setting, unit from pg_settings where name = 'wal_segment_size';
> > setting | unit
> > ----------+------
> > 16777216 | B
> >
> > So, while the WAL segment size used to be expressed in terms of 8K pages
> > it is now expressed in terms of absolute bytes. This seemed to me to be
> > a very deliberate change in the original commit so I guessed it was done
> > for clarity, but that the docs didn't get the message.
>
> Thoughts on this?
>
> I know it's minor in the grand scheme of things but it caused me some
> confusion when I was updating pgBackRest for v11 and I imagine it might
> do the same for others.
Sorry for forgetting this, pushed.
I kinda wonder whether we should move a few GUCs out of the
<sect1 id="runtime-config-preset">
section. Or adapt its description. Because a significant portion of its
contents don't accurately seem to be described by
The following <quote>parameters</quote> are read-only, and are determined
when <productname>PostgreSQL</productname> is compiled or when it is
installed.
right?
Greetings,
Andres Freund
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To: pgsql-committers@postgresql.org
Cc: andres@anarazel.de, david@pgmasters.net
Subject: Re: pgsql: Make WAL segment size configurable at initdb time.
In-Reply-To: <20181110033052.xmmozibdapwvenkx@alap3.anarazel.de>
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