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Date: Fri, 13 Nov 2020 11:32:23 +0800
From: "lchch1990@sina.cn" <lchch1990@sina.cn>
To: "Masahiro Ikeda" <ikedamsh@oss.nttdata.com>
Cc: "Amit Kapila" <amit.kapila16@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Add statistics to pg_stat_wal view for wal related parameter
 tuning
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charse=
t=3DISO-8859-1"><style>body { line-height: 1.5; }blockquote { margin-top: =
0px; margin-bottom: 0px; margin-left: 0.5em; }body { font-size: 10.5pt; fo=
nt-family: 'Microsoft YaHei UI'; color: rgb(0, 0, 0); line-height: 1.5; }<=
/style></head><body>=0A<div><span></span><br></div><div><div>&gt;Now, pg_s=
tat_wal supports reset all informantion in WalStats</div><div><span style=
=3D"font-size: 10.5pt; line-height: 1.5; background-color: transparent;">&=
gt;</span>using pg_stat_reset_shared('wal') function.</div><div><span styl=
e=3D"font-size: 10.5pt; line-height: 1.5; background-color: transparent;">=
&gt;</span>Isn't it enough?</div></div><div>Yes it ok, sorry I miss this i=
nfomation.</div><div><br></div><div><br></div><div><div>&gt;&gt; 3. I do n=
ot think it's a correct describe in document for</div><div>&gt;&gt; 'wal_b=
uffers_full'.</div><div>&nbsp;</div><div>&gt;Where should I rewrite the de=
scription? If my understanding is not</div><div>&gt;correct, please let me=
 know.</div></div><div>Sorry I have not described it clearly, because I ca=
n not understand the meaning of&nbsp;<span style=3D"font-size: 10.5pt; lin=
e-height: 1.5; background-color: transparent;">this</span></div><div><span=
 style=3D"font-size: 10.5pt; line-height: 1.5; background-color: transpare=
nt;">column after I read the describe in document.</span></div><div><span =
style=3D"font-size: 10.5pt; line-height: 1.5; background-color: transparen=
t;">And now I read the source code of walwrite and found the place where '=
</span><span style=3D"background-color: transparent;">wal_buffers_full</sp=
an><span style=3D"font-size: 10.5pt; line-height: 1.5; background-color: t=
ransparent;">'</span></div><div><span style=3D"font-size: 10.5pt; line-hei=
ght: 1.5; background-color: transparent;">added is for a&nbsp;</span><span=
 style=3D"font-size: 10.5pt; line-height: 1.5; background-color: transpare=
nt;">backend to wait a wal buffer which is&nbsp;</span><span style=3D"back=
ground-color: transparent;">occupied by other wal page, so the&nbsp;</span=
></div><div><span style=3D"font-size: 10.5pt; line-height: 1.5; background=
-color: transparent;">backend flush the old page in the wal buffer(after w=
ait it can).</span></div><div><span style=3D"font-size: 10.5pt; line-heigh=
t: 1.5; background-color: transparent;">So i think the origin decribe in d=
ocument is not so in point, we can describe it such as</span></div><div><s=
pan style=3D"font-size: 10.5pt; line-height: 1.5; background-color: transp=
arent;">'</span><span style=3D"background-color: transparent;">Total&nbsp;=
</span><span style=3D"font-size: 10.5pt; line-height: 1.5; background-colo=
r: transparent;">number of times WAL data written to the disk because a ba=
ckend&nbsp;</span><span style=3D"font-size: 10.5pt; line-height: 1.5; back=
ground-color: transparent;">yelled a wal buffer</span></div><div><span sty=
le=3D"background-color: transparent;">for an advanced wal page.</span></di=
v><div><span style=3D"background-color: transparent;"><br></span></div><di=
v><span style=3D"background-color: transparent;">Sorry if my understand is=
 wrong.</span></div><div><br></div><div><br></div>=0A<div><br></div><block=
quote style=3D"margin-Top: 0px; margin-Bottom: 0px; margin-Left: 0.5em; ma=
rgin-Right: inherit"><div>=0A</div></blockquote>=0A</body></html>
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