Date: Mon, 16 Jun 2025 12:59:57 -0400
From: Richard Welty <rwelty@salesium.com>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "adolfo flores" <adolfoflores2211@gmail.com>,
	"pgsql-general" <pgsql-general@lists.postgresql.org>
Message-Id: <19779aef09c.f35a7edd116750.8002494421662785732@salesium.com>
In-Reply-To: <536522.1750091949@sss.pgh.pa.us>
References: <CADM4kyuO39mr8E_xDw4GGi2v9gCK0dq52fKj40FcsXJeKxgRrA@mail.gmail.com> <536522.1750091949@sss.pgh.pa.us>
Subject: Re: Getting error "too many clients already" despite having a db
 connection limit set
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a coding error i've seen from inexperienced devs with little database exper=
ience

is inattentiveness to how the DB connections were being opened. last time i

saw this, a smart young dev with no DB background did not understand the co=
st

of opening connections and had on the order of 30 php calls to open connect=
ions

to PostgreSQL in a single page. he did not understand why it was slow.


richard


---- On Mon, 16 Jun 2025 12:39:09 -0400 Tom Lane <tgl@sss.pgh.pa.us> wrote =
---


adolfo flores < mailto:adolfoflores2211@gmail.com > writes:=20
> I hope you can help me with an issue we're experiencing. We have an app=
=20
> running on Kubernetes that opens a huge number of connections within a=20
> couple of seconds.=20
=20
You need to fix that app to be less unfriendly, or maybe put it behind=20
a connection pooler.=20
=20
> Is it expected behavior to reach the max_connections limit when that app=
=20
> opens many connections in a short period of time, even if a connection=20
> limit is set for that database and everything else uses no more than 10% =
of=20
> the max_connections?=20
=20
It takes a finite amount of time for a new backend process to figure=20
out which database it's supposed to connect to and then detect whether=20
the per-DB connection limit is exceeded.  In the meantime, that=20
session does count against the global limit, so yeah this isn't=20
surprising if the connection arrival rate is high enough.=20
=20
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0reg=
ards, tom lane
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head>=
<meta content=3D"text/html;charset=3DUTF-8" http-equiv=3D"Content-Type"></h=
ead><body ><div style=3D"font-family: Verdana, Arial, Helvetica, sans-serif=
; font-size: 10pt;"><div>a coding error i've seen from inexperienced devs w=
ith little database experience<br></div><div>is inattentiveness to how the =
DB connections were being opened. last time i<br></div><div>saw this, a sma=
rt young dev with no DB background did not understand the cost<br></div><di=
v>of opening connections and had on the order of 30 php calls to open conne=
ctions<br></div><div>to PostgreSQL in a single page. he did not understand =
why it was slow.<br></div><div><br></div><div>richard</div><div><br></div><=
div class=3D"zmail_extra_hr" style=3D"border-top: 1px solid rgb(204, 204, 2=
04); height: 0px; margin-top: 10px; margin-bottom: 10px; line-height: 0px;"=
><br></div><div class=3D"zmail_extra" data-zbluepencil-ignore=3D"true"><div=
><br></div><div id=3D"Zm-_Id_-Sgn1">---- On Mon, 16 Jun 2025 12:39:09 -0400=
 <b>Tom Lane &lt;tgl@sss.pgh.pa.us&gt;</b> wrote ---<br></div><div><br></di=
v><blockquote style=3D"margin: 0px;" id=3D"blockquote_zmail"><div>adolfo fl=
ores &lt;<a target=3D"_blank" href=3D"mailto:adolfoflores2211@gmail.com">ad=
olfoflores2211@gmail.com</a>&gt; writes: <br>&gt; I hope you can help me wi=
th an issue we're experiencing. We have an app <br>&gt; running on Kubernet=
es that opens a huge number of connections within a <br>&gt; couple of seco=
nds. <br> <br>You need to fix that app to be less unfriendly, or maybe put =
it behind <br>a connection pooler. <br> <br>&gt; Is it expected behavior to=
 reach the max_connections limit when that app <br>&gt; opens many connecti=
ons in a short period of time, even if a connection <br>&gt; limit is set f=
or that database and everything else uses no more than 10% of <br>&gt; the =
max_connections? <br> <br>It takes a finite amount of time for a new backen=
d process to figure <br>out which database it's supposed to connect to and =
then detect whether <br>the per-DB connection limit is exceeded.  In the me=
antime, that <br>session does count against the global limit, so yeah this =
isn't <br>surprising if the connection arrival rate is high enough. <br> <b=
r>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;r=
egards, tom lane <br> <br> <br></div></blockquote></div><div><br></div></di=
v><br></body></html>
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