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)

PHP 8.1 と PostgreSQL で、提供された PHP の再現コードを pg_connect()、pg_query()、pg_field_type() とともに使い、最初の呼び出しとそれ以降の呼び出しを比較することから始めます。最初の呼び出しに約 46 ms かかる理由を特定するため、PostgreSQL のフィールド型検索パスを追跡します。完了の条件は、最初の呼び出しに原因不明の遅延がなくなり、観測された時間がリグレッションチェックでカバーされていることです。