<?php

$sql = '
SELECT
    RDB$PROCEDURE_NAME AS NAME,
    RDB$PROCEDURE_SOURCE AS SRC
--    CAST(SUBSTRING(RDB$PROCEDURE_SOURCE FROM 1 FOR 8191) AS VARCHAR(8191)) AS SRC
FROM
    RDB$PROCEDURES   
';

try {
    $dbh = new \PDO('firebird:dbname=localhost:test', 'SYSDBA', 'masterkey');
    $dbh->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
    $dbh->setAttribute(\PDO::ATTR_EMULATE_PREPARES, false);
    $dbh->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_NATURAL);
    //$dbh->setAttribute(\PDO::ATTR_AUTOCOMMIT, false);

    echo "First used: " . memory_get_usage(true) . "<br>";
 
  
    for ($i = 0; $i < 20; $i++) {
	//$dbh->beginTransaction();
        $sth = $dbh->prepare($sql);
        $sth->execute();          
        $rows = $sth->fetchAll();
	unset($rows);
        //$sth->closeCursor();
	unset($sth);
	//$dbh->commit();
        echo "$i itteration used: " . memory_get_usage(true) . "<br>";
    }
    unset($dbh);
    echo "Last used: " . memory_get_usage(true) . "<br>";
} catch (\Exception $e) {
    echo $e->getMessage();
}

try {
    $dbh = new \PDO('firebird:dbname=localhost:horses', 'SYSDBA', 'masterkey');
    $dbh->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
    $dbh->setAttribute(\PDO::ATTR_EMULATE_PREPARES, false);
    $dbh->setAttribute(\PDO::ATTR_CASE, \PDO::CASE_NATURAL);

$sql = '
SELECT
    RDB$PROCEDURE_NAME AS NAME,
    RDB$PROCEDURE_SOURCE AS SRC
FROM
    RDB$PROCEDURES   
';

    echo "First used: " . memory_get_usage(true) . "<br>";
  
    for ($i = 0; $i < 20; $i++) {
        $sth = $dbh->prepare($sql);
        $sth->execute();          
        $rows = $sth->fetchAll();
	    unset($rows);
	    unset($sth);
        echo "$i itteration used: " . memory_get_usage(true) . "<br>";
    }
    unset($dbh);
    echo "Last used: " . memory_get_usage(true) . "<br>";
}
catch(Exception $e) {
	var_dump($e);
}

First used: 2097152
0 itteration used: 2097152
1 itteration used: 2097152
2 itteration used: 2097152
3 itteration used: 2097152
4 itteration used: 2097152
5 itteration used: 2097152
6 itteration used: 2097152
7 itteration used: 2097152
8 itteration used: 2097152
9 itteration used: 2097152
10 itteration used: 2097152
11 itteration used: 2097152
12 itteration used: 2097152
13 itteration used: 2097152
14 itteration used: 2097152
15 itteration used: 2097152
16 itteration used: 2097152
17 itteration used: 2097152
18 itteration used: 2097152
19 itteration used: 2097152
Last used: 2097152