Re: Delays between "connection received" and "connection authenticated" because of localhost entries in hba

[Adrian Klaver]

On 10/29/24 09:30, Daniel Westermann (DWE) wrote:

Delays between "connection received" and "connection authenticated" because of 
localhost entries in hba

Hi,

we're facing a strange issue with delays between "connection received" and 
"connection authenticated".

# select version();
                                                               version
-----------------------------------------------------------------------------------------------------------------------------------
  PostgreSQL 15.6 (Ubuntu 15.6-1.pgdg22.04+1) on x86_64-pc-linux-gnu, compiled 
by gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit
(1 ligne)

I know, this is not the latest minor version.

# \! cat /etc/os-release | head -1
PRETTY_NAME="Ubuntu 22.04.4 LTS"

What we see in the log is this (around 4 seconds delay):

2024-05-07 15:29:50.244 CEST [369909] LOG:  connection received: 
host=xx.xx.xx.100 port=48434
2024-05-07 15:29:54.518 CEST [369909] LOG:  connection authenticated: 
identity="xxxxxx" method=md5 (/etc/postgresql/15/main/pg_hba.conf:121)

1) host=xx.xx.xx.100 = localhost?

2) In postgresql.conf what is listen_addresses set to?

3) What are the settings in /etc/hosts?

The matching line is this ( I know md5 ):
host    all             xxxxx     xx.xx.xx.0/24            md5

What we've found out so far is, that this only happens if we have a 
localhost(or any other hostname) line before the line matching our connection, 
something like this:
host    replication     xxxxx     localhost                md5
host    all             xxxxx     xx.xx.xx.0/24            md5

We don't see it if we do it like this:
host    all             xxxxx     xx.xx.xx.0/24            md5
host    replication     xxxxx     localhost                md5

Has anyone experienced such a behavior? It seems clear that this is somehow 
related to name resolution but we couldn't reproduce something like this on the 
OS using dig (in a loop several hundred of times). It is also only happening 
from time to time, and not constantly.

What we're basically looking for is a way to prove the assumption without 
involving PostgreSQL at all, if that does make sense?

Many thanks in advance
Daniel

--
Adrian Klaver
adrian.kla...@aklaver.com