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Date: Fri, 8 Feb 2013 01:38:09 -0800
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 <CABBDWwfVg275EjUd0daBN7Vd9yaCZewSgbzd3_8ciEXY5XK0tQ@mail.gmail.com>
Subject: The relation between "checkpoint_timeout" and
	"checkpoint_warning" is missing
From: Tianyin Xu <tixu@cs.ucsd.edu>
To: pgsql-docs@postgresql.org
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Hi, PG,

In "18.5.2. Checkpoints" (
http://www.postgresql.org/docs/9.2/static/runtime-config-wal.html#RUNTIME-CONFIG-WAL-CHECKPOINTS),
the relation between "checkpoint_timeout" and "checkpoint_warning" is
missing.

According to the code, "checkpoint_timeout" should be set larger than
"checkpoint_warning", otherwise the warnings will not be generated. The
comments in function: CheckpointerMain() also tell such behavior, which is
in line#473 in "src/backend/postmaster/checkpointer.c":

/*
 * We will warn if (a) too soon since last checkpoint (whatever
 * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
 * since the last checkpoint start.  Note in particular that this
 * implementation will not generate warnings caused by
 * CheckPointTimeout < CheckPointWarning.
 */

I think this's should definitely specified in the documentation.

Best,
Tianyin


-- 
Tianyin XU,
http://cseweb.ucsd.edu/~tixu/

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<div dir=3D"ltr">Hi, PG,<div><br></div><div>In &quot;18.5.2. Checkpoints&qu=
ot; (<a href=3D"http://www.postgresql.org/docs/9.2/static/runtime-config-wa=
l.html#RUNTIME-CONFIG-WAL-CHECKPOINTS" target=3D"_blank">http://www.postgre=
sql.org/docs/9.2/static/runtime-config-wal.html#RUNTIME-CONFIG-WAL-CHECKPOI=
NTS</a>), the relation between=A0&quot;checkpoint_timeout&quot; and &quot;c=
heckpoint_warning&quot; is missing.=A0</div>

<div><br></div><div>According to the code,=A0&quot;checkpoint_timeout&quot;=
 should be set larger than &quot;checkpoint_warning&quot;, otherwise the wa=
rnings will not be generated. The comments in function: CheckpointerMain() =
also tell such behavior, which is in line#473 in &quot;src/backend/postmast=
er/checkpointer.c&quot;:</div>

<div><br></div><div><div>/*</div><div>=A0* We will warn if (a) too soon sin=
ce last checkpoint (whatever</div><div>=A0* caused it) and (b) somebody set=
 the CHECKPOINT_CAUSE_XLOG flag</div><div>=A0* since the last checkpoint st=
art. =A0Note in particular that this</div>

<div>=A0* implementation will not generate warnings caused by</div><div>=A0=
* CheckPointTimeout &lt; CheckPointWarning.</div><div>=A0*/</div></div><div=
><br></div><div>I think this&#39;s should definitely specified in the docum=
entation.</div>

<div><br></div><div>Best,</div><div>Tianyin=A0</div><div><br clear=3D"all">=
<div><br></div>-- <br><span style=3D"text-indent:0px;letter-spacing:normal;=
font-variant:normal;text-align:-webkit-auto;font-style:normal;font-weight:n=
ormal;line-height:normal;border-collapse:separate;text-transform:none;font-=
size:medium;white-space:normal;font-family:&#39;Times New Roman&#39;;word-s=
pacing:0px"><span style=3D"color:rgb(102,102,102);font-family:arial;font-si=
ze:small">Tianyin XU,<br>

<a href=3D"http://cseweb.ucsd.edu/%7Etixu/" target=3D"_blank">http://cseweb=
.ucsd.edu/~tixu/</a></span></span>
</div></div>

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