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)

Comienza con la reproducción de PHP proporcionada usando pg_connect(), pg_query() y pg_field_type() en PHP 8.1 con PostgreSQL, comparando la primera llamada con las posteriores. Traza la ruta de búsqueda del tipo de campo de PostgreSQL para identificar por qué la primera llamada tarda unos 46 ms; se considera terminado cuando la primera llamada ya no presenta el retraso inexplicado y el tiempo observado está cubierto por una comprobación de regresión.