MIME-Version: 1.0
References: <a58f1c38-10eb-7d7f-372c-cfb95007d54e@enterprisedb.com>
 <20211224.143725.1750248643492340056.horikyota.ntt@gmail.com>
 <ad83e515-44f6-4691-8fe0-503b94499ed5@enterprisedb.com>
 <20211224.170451.116141220257426861.horikyota.ntt@gmail.com>
 <27f005a6-63f7-2ca9-2ab3-92fe9110e224@enterprisedb.com>
 <b652ce45-8d85-fe78-2914-8993692c2ee0@oss.nttdata.com>
In-Reply-To: <b652ce45-8d85-fe78-2914-8993692c2ee0@oss.nttdata.com>
From: Sascha Kuhl <yogidabanli@gmail.com>
Date: Tue, 28 Dec 2021 09:28:30 +0100
Message-ID: 
 <CAPvVvKDjqozx5szNTRthNiFePBvPT+Td0e8rqjb23oF8Py4e6A@mail.gmail.com>
Subject: Re: sequences vs. synchronous replication
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Content-Type: multipart/alternative; boundary="000000000000e2228305d4309bf3"
Archived-At: 
 <https://www.postgresql.org/message-id/CAPvVvKDjqozx5szNTRthNiFePBvPT%2BTd0e8rqjb23oF8Py4e6A%40mail.gmail.com>
Precedence: bulk

--000000000000e2228305d4309bf3
Content-Type: text/plain; charset="UTF-8"

Sequence validation by step, in total is great. If the sequence is Familie
or professional, does it make sense to a have a total validation by an
expert. I can only say true by chi square Networks, but would a medical
opinion be an improvement?

Fujii Masao <masao.fujii@oss.nttdata.com> schrieb am Di., 28. Dez. 2021,
07:56:

>
>
> On 2021/12/24 19:40, Tomas Vondra wrote:
> > Maybe, but what would such workload look like? Based on the tests I did,
> such workload probably can't generate any WAL. The amount of WAL added by
> the change is tiny, the regression is caused by having to flush WAL.
> >
> > The only plausible workload I can think of is just calling nextval, and
> the cache pretty much fixes that.
>
> Some users don't want to increase cache setting, do they? Because
>
> - They may expect that setval() affects all subsequent nextval(). But if
> cache is set to greater than one, the value set by setval() doesn't affect
> other backends until they consumed all the cached sequence values.
> - They may expect that the value returned from nextval() is basically
> increased monotonically. If cache is set to greater than one, subsequent
> nextval() can easily return smaller value than one returned by previous
> nextval().
> - They may want to avoid "hole" of a sequence as much as possible, e.g.,
> as far as the server is running normally. If cache is set to greater than
> one, such "hole" can happen even thought the server doesn't crash yet.
>
>
> > FWIW I plan to explore the idea of looking at sequence page LSN, and
> flushing up to that position.
>
> Sounds great, thanks!
>
> Regards,
>
> --
> Fujii Masao
> Advanced Computing Technology Center
> Research and Development Headquarters
> NTT DATA CORPORATION
>
>
>

--000000000000e2228305d4309bf3
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir=3D"auto">Sequence validation by step, in total is great. If the se=
quence is Familie or professional, does it make sense to a have a total val=
idation by an expert. I can only say true by chi square Networks, but would=
 a medical opinion be an improvement?</div><br><div class=3D"gmail_quote"><=
div dir=3D"ltr" class=3D"gmail_attr">Fujii Masao &lt;<a href=3D"mailto:masa=
o.fujii@oss.nttdata.com">masao.fujii@oss.nttdata.com</a>&gt; schrieb am Di.=
, 28. Dez. 2021, 07:56:<br></div><blockquote class=3D"gmail_quote" style=3D=
"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
<br>
On 2021/12/24 19:40, Tomas Vondra wrote:<br>
&gt; Maybe, but what would such workload look like? Based on the tests I di=
d, such workload probably can&#39;t generate any WAL. The amount of WAL add=
ed by the change is tiny, the regression is caused by having to flush WAL.<=
br>
&gt; <br>
&gt; The only plausible workload I can think of is just calling nextval, an=
d the cache pretty much fixes that.<br>
<br>
Some users don&#39;t want to increase cache setting, do they? Because<br>
<br>
- They may expect that setval() affects all subsequent nextval(). But if ca=
che is set to greater than one, the value set by setval() doesn&#39;t affec=
t other backends until they consumed all the cached sequence values.<br>
- They may expect that the value returned from nextval() is basically incre=
ased monotonically. If cache is set to greater than one, subsequent nextval=
() can easily return smaller value than one returned by previous nextval().=
<br>
- They may want to avoid &quot;hole&quot; of a sequence as much as possible=
, e.g., as far as the server is running normally. If cache is set to greate=
r than one, such &quot;hole&quot; can happen even thought the server doesn&=
#39;t crash yet.<br>
<br>
<br>
&gt; FWIW I plan to explore the idea of looking at sequence page LSN, and f=
lushing up to that position.<br>
<br>
Sounds great, thanks!<br>
<br>
Regards,<br>
<br>
-- <br>
Fujii Masao<br>
Advanced Computing Technology Center<br>
Research and Development Headquarters<br>
NTT DATA CORPORATION<br>
<br>
<br>
</blockquote></div>

--000000000000e2228305d4309bf3--