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Re: Getting error "too many clients already" despite having a db connection limit set - Mailing list pgsql-general

From Richard Welty
Subject Re: Getting error "too many clients already" despite having a db connection limit set
Date
Msg-id 19779aef09c.f35a7edd116750.8002494421662785732@salesium.com
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In response to Re: Getting error "too many clients already" despite having a db connection limit set  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-general
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a coding error i've seen from inexperienced devs with little database experience
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 cost
of opening connections and had on the order of 30 php calls to open connections
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 <adolfoflores2211@gmail.com> writes:
> I hope you can help me with an issue we're experiencing. We have an app
> running on Kubernetes that opens a huge number of connections within a
> couple of seconds.

You need to fix that app to be less unfriendly, or maybe put it behind
a connection pooler.

> Is it expected behavior to reach the max_connections limit when that app
> opens many connections in a short period of time, even if a connection
> limit is set for that database and everything else uses no more than 10% of
> the max_connections?

It takes a finite amount of time for a new backend process to figure
out which database it's supposed to connect to and then detect whether
the per-DB connection limit is exceeded. In the meantime, that
session does count against the global limit, so yeah this isn't
surprising if the connection arrival rate is high enough.

            regards, tom lane




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