pg_field_type first call is very slow

Description

Problem: function pg_field_type first call (after run php script) is very slow.
The following code:

$connection = pg_connect("...") or die('Cannot connect db');
$res = pg_query($connection, 'SELECT 100');

$time0 = microtime(true); pg_field_name($res, 0);
$out[] = '(query 1) pg_field_name() first call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

$time0 = microtime(true); pg_field_size($res, 0);
$out[] = '(query 1) pg_field_size() first call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

$time0 = microtime(true); pg_field_type($res, 0);
$out[] = '(query 1) pg_field_type() first call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

$time0 = microtime(true); pg_field_type($res, 0);
$out[] = '(query 1) pg_field_type() second call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

$res = pg_query($connection, 'SELECT 200');

$time0 = microtime(true); pg_field_type($res, 0);
$out[] = '(query 2) pg_field_type() first call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

$time0 = microtime(true); pg_field_type($res, 0);
$out[] = '(query 2) pg_field_type() second call = '.number_format((microtime(true) - $time0) * 1000, 4).' мс';

print_r($out);
<?php

Resulted in this output:

Array (
    [0] => "(query 1) pg_field_name() first call = 0.0069 мс"
    [1] => "(query 1) pg_field_size() first call = 0.0031 мс"
    [2] => "(query 1) pg_field_type() first call = 46.6821 мс"  // FIRST CALL IS VERY SLOW (pg_field_type)
    [3] => "(query 1) pg_field_type() second call = 0.0050 мс"
    [4] => "(query 2) pg_field_type() first call = 0.0069 мс"
    [5] => "(query 2) pg_field_type() second call = 0.0029 мс"
)

But I expected this output instead:

Array (
    [0] => "(query 1) pg_field_name() first call = 0.0069 мс"
    [1] => "(query 1) pg_field_size() first call = 0.0031 мс"
    [2] => "(query 1) pg_field_type() first call = 0.0050-0.0069 мс"  // MUST BE
    [3] => "(query 1) pg_field_type() second call = 0.0050 мс"
    [4] => "(query 2) pg_field_type() first call = 0.0069 мс"
    [5] => "(query 2) pg_field_type() second call = 0.0029 мс"
)

PHP Version

PHP 8.1

Operating System

Debian 11 (bullseye)

Commencez avec la reproduction PHP fournie en utilisant pg_connect(), pg_query() et pg_field_type() sur PHP 8.1 avec PostgreSQL, en comparant le premier appel aux appels suivants. Suivez le chemin de recherche du type de champ de PostgreSQL afin d’identifier pourquoi le premier appel prend environ 46 ms ; le travail est terminé lorsque le premier appel ne présente plus le délai inexpliqué et que le temps observé est couvert par une vérification de régression.