PHP + PostgreSQL Lightweighted Caching

gistfile1.php

<?
    $connection_string = '*insert connection string here*';
    $cache_id = 123;
    $expiration_seconds = 86400;
    
    function generate_a_huge_string() {
        sleep(5);
        return 'An awesome string has been generated!';
    }
    
    date_default_timezone_set('UTC');
    $pg = pg_pconnect($connection_string) or die('Unable to connect to PostgreSQL!');
    pg_query($pg, <<<'Query'
        CREATE TABLE IF NOT EXISTS Cache (
            id      BIGINT NOT NULL PRIMARY KEY,
            data    TEXT NOT NULL,
            time    TIMESTAMP NOT NULL default (now() at time zone 'utc')
        );
        
        CREATE OR REPLACE FUNCTION upsertCache(a BIGINT, b TEXT) RETURNS VOID AS
        $$
        BEGIN
            LOOP
                UPDATE Cache SET data = b, time = now() at time zone 'utc' WHERE id = a;
                IF found THEN
                    RETURN;
                END IF;
                BEGIN
                    INSERT INTO Cache (id, data) VALUES (a, b);
                    RETURN;
                EXCEPTION WHEN unique_violation THEN
                END;
            END LOOP;
        END;
        $$
        LANGUAGE plpgsql;
Query
    ) or die('Initialization failed.');
    
    // show-cache.php
    $query = pg_query($pg, "SELECT data, time FROM Cache WHERE id = $cache_id")
        or die('Unable to query data in the database.');
    echo ($entry = pg_fetch_array($query)) ? $entry['data']
                                           : '<div class="center">Cache unavailable, please retry later.</div>';
    if (!$entry || time() - strtotime($entry['time']) > $expiration_seconds)
        echo '<script src="refresh-cache.php" async></script>';
    
    // refresh-cache.php
    pg_query($pg, "SELECT upsertCache($cache_id, '" . pg_escape_string($pg, generate_a_huge_string()) . "');")
        or die('Unable to update data in the database.');
?>